the universal prosthesis -- report 2005-11-18

February - November 2005The Universal ProsThesis - rePorT

FeasibiliTy oF The Universal below-knee ProsThesis aHands-OffPTB/TCB-HybridProsthesis withaLow-ExpertiseFittingMethod.

Written by:

Boudewijn Wisse

Mentors:

Johan Molenbroek

Marc Tassoul

Just Herder

Delft University of Technology

Faculty of Industrial Design Engineering

The Netherlands

II

This report is about a quest to improve pros-thesis for lower-limb amputees and is a result of my graduation project.

Although estimations vary wildly, it is cer-tain that there are millions of limbless people in the world. In 2002 I went to Sri Lanka to see if my expertise (product design) could help at least some of them. All my tries, trials and adventures led to my graduation, of which this first report is lying in front of you. I hope you will find the report informative and inspiring.

It all started with a contest by Johan Molenbroek and Henk Kooistra, who asked several groups of industrial design engineers to think about the land mine-victims in Sri Lanka. I entered the “Design for All” com-petition and was able to continue with an internship in Sri Lanka. Now, two years and much thinking later, I started this graduation project.

In practice, this project is about the design of a universal transtibial prosthesis. Imagine a comfortable, adaptable and adjustable leg prosthesis, suitable for people with different residual limb shapes and sizes! It could reach at least some of the millions limbless, who now cannot receive the health care and prod-uct they need. I hope my graduation project will prove the universal prosthesis is feasible, so production can be started and amputees can be reached and benefit from this work.

This report came into being from February to May 2005, at the faculty of Industrial Design Engineering, at the Delft University of Technology in the Netherlands. I would like to thank Just Herder, Marc Tassoul and Johan Molenbroek for their kind assistance and Wouter van Dorsser for his never ending support. Every day I work on this project , I think about all the knowledge the people in Sri Lanka taught me. Thanks again.

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The Universal ProsthesisBoudewijn Martin Wisse

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sUmmary

The universal transtibial prosthesis is a below-knee prosthesis that can be fitted to the amputees residual limb by an inexperienced person. Due to the lack of (time of) prosthetist in many countries, amputees world-wide can profit from better health care because of the Universal Prosthesis. Nowadays, still one mil-lion people are in need of an artificial limb.

The Universal Prosthesis primarily consists of a socket-pylon frame, a connective compo-nent to the foot and a “liner” that will func-tion as the inner and outer layer of the socket, and an injector.

During the fitting procedure the frame transfers half the weight of the body of the amputee to the residual limb’s pressure-toler-ant areas. Then, a total contact fit is achieved by filling the inner and outer layer of the socket with rigid Poly-Urethane foam. The injector, that provides the foam, is basically a high-pressure aerosol spray with a special nozzle.

Because the frame loads the pressure toler-ant areas (in particular the patellar tendon) and the injector pressurizes the inner space of the socket during fabrication, the socket is a patellar-tendon-bearing / total-contact-bearing hybrid. (PTB-TCS-hybrid). This way, maximal comfort is achieved. The precise,

volume-matching fit provides good control over the prosthesis to the user.

The socket-pylon frame forms an exoskeletal design, with good stiffness and strength. The pylon is connected to the foot by a connec-tive component with a pivot point. In this way, dynamic alignment or alignment adjust-ments stay possible after the fabrication of the socket, though limited in respect to state-of-the-art modular endoskeletal designs.

Suspension is achieved by supracondy-lar brims. In cases where this suspension is insufficient, a suspension sleeve can be added.

The fitting procedure results in a prosthesis that can be used daily, in the same way as currently available designs.

Apart from the injector, which is part of the distribution kit containing all components, no tools are needed that can not be found in local hardware stores to fit the prosthe-sis (basically, a saw and a screwdriver). The Universal Prosthesis is independent of local infrastructure which enables a broad and easy distribution.

Markets for the Universal Prosthesis include temporal, spare prostheses, and definite pros-theses, especially for elder and still growing children. When fully developed and opti-mized, the Universal Prosthesis can be used for amputees worldwide in all circumstances. Because of variations in residual limb shape, length and health, the Universal Prosthesis is suitable for about 70% of the transtibial amputees in the target groups.

Price of the Universal Prosthesis can vary widely and is dependent on the amount of pieces produced a year. Market exploitation in developed countries becomes commercially feasible at a price for the distribution kit that is lower than 700 USD. Worldwide market exploitation of the Universal Prosthesis becomes commercially feasible at prices of the 100-200 USD, dependent on the situation of the users and the support of NGOs and aid-funds. To reach these prices, development and organisation of the Universal Prosthesis from this report to European distribution and from that to worldwide distribution both have to stay under 1,000,000 USD.

IV

Field studies have to prove the effectiveness of the Universal Prosthesis and will provide feedback for further improvements. These field studies are the next big step towards implementation. However, literature shows that one prefabricated socket can already be successfully used for 50% of the transtibial amputees. Outcome is expected to indicate that the Universal Prosthesis is suitable for 70-80% of the transtibial amputees.

Concluding, the development and implemen-tation of the Universal Prosthesis is feasible.

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Table oF conTenTs

1 IntroductIon __________________ 1

2 ProjectBackgroundandaPProach _____________________ 2

2.1 tImeLIneofProjectanddesIgnPhILosoPhy ___________________ 2

2.2 theneedformoreProsthetIsts __________________ 3

2.3 recommendatIon:theunIversaLProsthesIs ____________________ 4

2.4 desIgnoBjectIve ______________ 5

2.5 ProjectaPProach _____________ 5

3 actorsandusers _____________ 6

3.1 thePatIent ___________________ 73.1.1 Anatomy of the Lower Limb ______ 73.1.2 Transtibial Amputations _________ 83.1.3 Residual Limbs _________________ 93.1.4 Patients Posture and Principles

for Alignment __________________ 133.1.5 Basic Biomechanics of Gait ______ 163.1.6 Gait Deviations ________________ 193.1.7 Special User Groups; children and

patients with a reduced activity level 20

3.2 theProsthetIstandotherteammemBersInaProsthetIccLInIc ____________ 21

3.3 ProducerofProstheses ______ 223.3.1 Dutch Industry ________________ 223.3.2 Worldwide Industry ____________ 223.3.3. Component and fitting prices ____ 23

4 transtIBIaLProstheses _______ 24

4.1 tyPesaccordIngtothePatIentsrehaBILItatIonstage _________ 25

4.1.1 Removable Rigid Dressing - RRD _ 264.1.2 Immediate Post Operative

Prosthesis - IPOP ______________ 274.1.3 Removable Protective Socket - RPS 284.1.4 Temporary Prosthesis __________ 294.1.5 Definite Prosthesis _____________ 30

4.2 structuraLdesIgns __________ 314.2.1 Exoskeletal Structure ___________ 314.2.2 Endoskeletal Structure __________ 32

4.3 comPonents _________________ 334.3.1 Basic Components: Socket _______ 334.3.2 Basic Components: Pylon _______ 364.3.3 Basic Components: Foot/Ankle

System _______________________ 374.3.4 Basic Components: Suspension __ 404.3.5 Additional Components _________ 434.3.6 Materials & Tools ______________ 44

4.4 BIomechanIcsoftranstIBIaLProstheses _______ 45

4.5 fInancIaLIssues&dIstrIButIon _________________ 49

4.5.1 To the Patient __________________ 494.5.2 To the Practitioner _____________ 504.5.3 To the Producer ________________ 504.5.4 To Governmental Institutions ____ 504.6 Repair and Life-time ____________ 50

VI

5 LIfewIthaProsthesIs-theamPutee’sPersPectIve ______ 51

5.1 PreProsthetIccare ___________ 52

5.2 seLectIngtheaId ____________ 53

5.3 aLIgnmentandrehaBILItatIon 54

5.4 daILyroutIne:donnIng,doffIngandgaIt _____________ 55

5.5 statIstIcsonfunctIonaLoutcomeanduse _____________ 58

5.6 aftercareandconcerns ______ 58

6 ethIcs,marketInganddesIgnvIsIon ________________________ 60

6.1 ethIcs________________________ 606.1.1 A World-wide Smart-tech product 606.1.2 Social-political consequences 60 6.1.3

A product for the world _________ 616.1.4 Production ____________________ 62

6.2 concLusIonsfromthesrILankantestdesIgns __________ 62

6.3 marketIng __________________ 63

6.4 suBstItuteProductsandcomPetItIvefIttIngmethods __ 65

6.4.1 Fabrication and fitting methods __ 656.4.2 Substitute products _____________ 66

6.5 vIsIonofthefIttIngProcedureandusage ____________________ 67

6.5.1 Cycle 1 – for developed countries 676.5.2 Cycle 2 – for developing countries 69

7 desIgncrIterIaandrequIrements 71

7.1 tendesIgncrIterIa _________ 71

7.2 requIrementsforcycLe0:thePreParatorydesIgntrajectory ___________________ 72

7.3 crIterIaforcycLe1:marketexPLoItatIonIndeveLoPedcountrIes __________ 73

7.4 crIterIaforcycLe2:worLdmarketexPLoItatIon __ 75

7.5 addItIonaLgoaLs _____________ 76

8 dIscussIonandconcLusIonofPart1 ____________________ 77

9 synthesIs-fromIdeatoProsthesIs ______ 79

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10 Ideas _________________________ 80

10.1 IdeageneratIon ______________ 80

10.2 IdeadIscussIon _______________ 81

10.3 IdeaseLectIonandIntegratIon 89

10.4 evaLuatIonoftheIntegrateddesIgnandconcLusIon ________ 90

11 concePt ______________________ 92

11.1 thehardsocket _____________ 9211.1.1 Selection of loadable and avoidable

area’s based on anatomy ________ 9211.1.2 Determining the rough frame

shape. ________________________ 9311.1.3 Optimizing the frame shape in

regards to the anatomy. _________ 9411.1.4 Back to 3D ____________________ 9511.1.5 Material choice ________________ 9611.1.6 Mechanical properties __________ 97

11.2 thesoftsocket _____________9811.2.1 Fitting liner ___________________ 9811.2.2 The Filler Material _____________ 9911.2.3 Adding pressure ______________ 101

11.3 theconnector ______________ 101

11.4 resuLtIngfIttIngProcedure _ 104

11.5 daILyusage&susPensIon ____ 105

11.6 ProductIonandPrIce ________ 10611.6.1 Production costs per part ______ 10611.6.2 Development costs ____________ 10711.6.3 Marketing and Distribution costs 10711.6.4 Conclusion ___________________ 108

12 evaLuatIon __________________ 109

12.1 scorIngcrIterIaIncomParIsonwIthotherProsthetIcsystems. __109

12.2 evaLuatIontheconcePtagaInsttherequIrements. ___________ 115

12.3 modeLandfItoftheframe _117

12.4 ProjectevaLuatIon __________ 119

12.5 concLusIons

13 recommandatIon ____________ 120

13.1 fundamentaLresearchInProsthetIcs. _________________ 120

13.2 ImProvIngtheunIversaLProsthesIs __________________ 121

13.3 ProjectcontInuatIon _______ 122

14 concLusIon __________________ 124

14.1 strengths ___________________ 124

14.2 ProjectProgressIon _________ 125

14.3 fInaLword __________________ 125

r references __________________ 126

F fIgures&taBLesList _______ 127

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1

The patient as well as the practitioner have to use and feel comfortable with the univer-sal prosthesis and are therefore the focus of the design process. In chapter 3 you will find a description of the actors and their relation-ships.

The design of the universal prosthesis will be based on existing knowledge, especially from current designs. Chapter 4 discusses current prostheses, existing types and their fabrication.

The prosthetist needs to fit and align the prosthesis, but the patient needs to wear it daily. Chapter 5 discusses the daily use of current designs.

These analysis, combined with the strategic principles from chapter 6, result in chapter 7 in the requirements as will be used for the design of the universal transtibial prosthe-ses.

Finally, in chapter 8, the conclusion states what needs to be done in the next phases of the project.

During previous projects [Wisse et al. 2002, 2003] it became clear that making, fitting and aligning prostheses for patients can be a time consuming activity. A universal prosthetic design for daily use could improve prosthetic health care, but is not yet available. Chapter 2 explains the source of this problem.

This is the first report of a project aiming to design such a prostheses. It exists of three parts:

I AnalysisII SynthesisIII Feasibility evaluation

i analysis

In the first part of this report, the analysis and preconditions for this project can be found. It concludes with the possibilities and the design requirements for a universal pros-thesis. This part will provide the information needed for the next phases in this research project. Those with some background in prosthetics and who are primary interested in the design requirements of the universal prosthesis are referred to chapter 6 and 7.

ii synThesis

In this part the development of a proof-of-principle concept of a universal socket is described. Chapter 9 describes the followed process to reach this result.

It all starts with the right ideas. Altough a strong vision and general idea about how the prosthesis should look like and function was generated in Part I, a new set of ideas is for-mulated to be sure that no good alternatives were overlooked (chapter 10).

This ideas need to be integrated into a new fitting method and the components of which the universal prosthesis is constructed. The parts are optimized to ensure one integral system in chapter 11.

iii FeasibiliTy sTUdy

The concept has to be evaluated (chapter 12). Will an universal prosthetic system become reality in the future? Chapter 13 gives some recommendations and an overview about what still needs to be done. Chapter 14 con-cludes with the answer to this question and gives a notion about what the future might bring.

1 inTrodUcTion

2

2 ProjectBackgroundandaPProach

This chapter will describe how the need for a universal prosthesis was recognised. It explains the underlying problem and the process that uncovered this problem.

Those who understand the need for a uni-versal prosthesis and are merely interested in the design analysis can skip to section 2.4.

2.1 timeLineofProjectanddesignPhiLosoPhy

While the project now focuses on a tech-nologically advanced product, it started out focusing on low cost, easy producible and repairable prosthesis for use in developing countries (see TABLE 2-1 and Appendix C for an overview).

In April 2002, Johan Molenbroek and Henk Kooistra started a “Design-for-All” contest in which several groups designed a prosthesis for Sri Lanka. Of course, I was part of a team that participated in this contest and the result was the report: “Prostheses for Sri-Lanka, prostheses for tibial amputees focused on the 3rd world “[Wisse et al. 2002] (See appendix A for a summary of the design for all project).

Mainly because of our force analyses and international approach, we won the contest and were able to continue our work in an internship in Sri Lanka. During the intern-ship, we worked at the Colombo Friends in Need Society (CFINS), a non-governmental organization (NGO). The CFINS provides pros-thetic services all over Sri Lanka and uses mainly the Jaipur Foot technology [Wisse et al. 2003, p13]. Here we were able to build and test some of our ideas from the contest. This resulted in a new design philosophy and new designs, which we were able to present at a World Congress of Alternative Medicine [Wisse et al. 2003]. Our results can be read in the report: “The Alternative Prosthesis, final report internship Sri Lanka 2002” [Wisse et al. 2003] (See appendix B for a summary of the internship).

(pre-) Sri Lanka This projectTime span Till December 2002 December 2004 till August 2005Problem per-ceived

Number of produced prosthesis too low

Number of professionals too low

Goal Prosthesis easy to manufacture from basic materials

Universal prosthesis from plastics

Target group Third world amputees Patients worldwideCosts Extremely low costs Cost reducing through time

Table2-1: Project targets before and after the Sri Lanka internship [Adjusted from Wisse et al. 2003, Chapter 5] (For a complete timeline see appendix C).

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At the start of the internship, the design ideas were based on three basic forms, namely our redesign of the prosthesis by Inne ten Have, the design by Michelle Kriesels and conventional prostheses. The prosthesis by Inne consists of a long strap of metal, which can be folded to form a patellar bearing pros-thesis [Wisse et al. 2002 for more informa-tion]. We initially improved it by adding some parts. Michelle Kriesels also participated in the “Design-for-All” contest and her design was based on (re)using bicycle parts to man-ufacture the prosthesis [Kriesels et al. 2002]. Of modern conventional prosthesis, the mod-ular build-up (See section 4.2) and the patel-lar tendon bearing principle (See section 4.3.1), were adopted to our designs.

However, during the internship, we found out that instead of producing prosthesis from aluminium, the advantages of using plastics were needed. Plastics offer a lot of design freedom for a decent final product price (only at higher quantities, so the product needs to be distributed to al least several countries). This design freedom is not only needed to provide a comfortable and stiff prosthesis, but moreover to assist the user in fitting and alignment. With plastics, primary functions, alignment functions and an adjustable shape can be integrated in one product. Costs are less an issue, as we see that US-Aid and other foundations have a “magical” 100$ border, which they are ready to pay for in case of humanitarian distribution of a prosthesis [Wisse et al. 2003].

For a flowchart of the socket designs till now, see Appendix D.

2.2 theneedformoreProsthetists

The “Design-for-All” contest’s goal was improving help for land-mine victims in Sri Lanka. However, because land mines are used in specific zones only, and Sri Lanka doesn’t suffer from sliding landmasses, civilian cau-salities are few. Still, the amount of amputees is Worldwide an problem.

Worldwide there are about 15 million amputees (also see appendix F). With 39 per-cent of them living in the Asia’s, this area deserves special attention. In some coun-tries land mines are a problem, though most common causes are accidents, diabetics, cancer, infections and congenital deformities.

Health care for the amputees is in many cases insufficient. The production capacity is low and there is a lack of experts (prosthetist) to fit the prostheses. “It has been estimated that it would require training up to 100,000 new prosthetists if conventional production methods are to meet the worldwide need” [Michael 1994]. This results in a lack in health care and aftercare. Although different groups are thinking about (and working on) this problem and developing alternatives, no alternatives are available yet.

4

In general a better use of the prosthetists‘ time will result in better overall care, more patients helped, better aftercare and more attention to difficult amputations and special patients (such as children).

There is a worldwide need For The ProsTheTisT’s valUable Time.

2.3 recommendation:theuniversaLProsthesis

As concluded in section 2.2, there is a need for more prosthetists.

Given a certain amount of amputees and the amount of care they need, the lack of prosthetists can be solved in three ways:

1 Increasing the amount of prosthetists.2 Lowering the level of experience (knowl-

edge) needed to be a prosthetist.3 Reducing the time asked per patient of the

prosthetists, which implies: - Reducing the need for replacement. - Reducing the time per adjustment

The design and manufacturing of the pros-thesis is a time-consuming event for the prosthetist. Research trails and prototypes strongly suggest that the prosthetist’s work can be more time-efficient with an alternative design for transtibial prostheses, the univer-sal prosthesis.

For developing countries, the philosophy for the universal prosthesis design could be as follows:

“A new concept for a everyday prostheses could improve the situation of amputees.

Evidence shows possibilities for an adjust-able, easy-to-fit but comfortable socket. The more the patient can do himself, the fewer prosthetists are needed, thus reducing the lack of prosthetists. The higher quantities needed for the newly reached amputees enable mass production. Costs are reduced. Distribution will speed up, because the need for the patient to travel to distribution points is cancelled. This prosthesis can be produced in developing countries, but has market potential all over the world. It is especially better suitable for children [Red: because it is adjustable and children and their residual limb keep growing].

Ideally, the end users are capable of adjust-ing the prostheses themselves. The product’s use should be self-explaining (e.g. by clues integrated in the product on how to use it).” [Adapted from Wisse et al. 2003].

Not only transtibial amputees will benefit in such a way. The freed production capac-ity can then be used to produce above knee prostheses or orthoses.

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2.4 designoBjective

It is clear that an easy-to-use, comfort-able, adjustable and durable prosthesis for daily use could result in better health care for amputees all over. However, the design requirements for a daily usable (definite) uni-versal prosthesis are quite high. Much devel-opment is needed before the definite univer-sal prosthesis is a reality.

Development of the universal prosthesis in stages (each with increasing design criteria) is a solution. As becomes clear later in the report, one possible stage is the universal prosthesis for use as a temporal prosthesis. Another possibility is developingthe prosthe-sis to be an avanced tool for prosthetists in developed countries.

To determine which stages or scenarios are beneficial to the project, this project starts with finding out what the possibilities are for a universal prosthesis (solution -> problem) instead of finding the universal prosthesis as the answer to a specific problem (problem -> solution).

The first step is to evaluate if the universal prosthesis is a feasible product at all. Such a feasibility study is most easily conducted at the hand of a “proof-of-principle” design. As suggested by the name, such a design proofs the concept of a universal prosthesis. Because

the comfort of the prosthesis’s fit is the most important functional outcome factor, this concept will focus on the development of the socket.

Concluding, the aim of this project is to design a concept of a universal prosthesis. This concept will be used to assess if the pro-duction of universal prostheses is feasible.

2.5 ProjectaPProach

This project will consist of three phases, that are parallel with the three parts of this report:

- Analysis- Concept design- Feasibility assessment

In which the major tasks are:

- Analysing the possible markets and target groups for a universal prosthesis. (this phase)

- Formulating a set of requirements. (this phase)

- Designing one or more concepts for (the socket of) a universal prosthesis. (second phase)

- Testing the best concept, preferably by testing a physical model /mock-up of the socket. (third phase)

- Assessing the feasibility of universal prosthe-ses in general and the concept in particular. (third phase)

Public

RevalidationTEAMAmputee

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Prosthetist

An analysis of the properties and behav-iour of the actors is necessary to determine the better part of the design requirements. The user is the most important actor. In the case of prosthetics, the amount of actors is huge (see figure 3-1). The focus on the project will be on those actors who deal with the prosthesis most intensively: the patient, the prosthetist and the producer.

Traditionally, prosthetic designs were mainly based on medical properties of the patient, especially the anatomy (of the residual limb) and biomechanics. Only recently more atten-tion has been given to the production (the modular design as discussed in section 4.2, is only developed in 1970 by the U.S. Veterans Administration). Now, high tech (such as microprocessor control of joints) solutions are sought. [Seymour 2002, p7]. However, till 2002, innovations for the patient or the prosthetist, were sparse.

In this chapter the three most important actors will be introduced: The patient (3.1), the prosthetist (3.2) and the producer of com-ponents (3.3). This chapter focusses on their properties. Their actions will be discussed later. Everyday use of the prosthesis by the patient will be discussed in chapter 5. Most use by the prosthetist will be discussed in chapter 4, together with the fabrication, alignment and fit of the prosthesis.

3 acTors and Users

The prosthesis is only part of the total care after an amputation and therefore in litera-ture a team approach in rehabilitation of the patient is often mentioned [Seymour 2002, Chapter 3]. The team approach will be shortly discussed in 3.2.

Figure3-1: The prosthesis and its total context.

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Dietician

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3.1.1 anaTomy oF The lower limb

Knowledge of the anatomy of the lower limb is the basic: it provides insight in which func-tions are lost by the amputa-tion and is a major inspira-tion in how to reintroduce them by means of a prosthesis. Figure 3-2 shows the most men-tioned bones and tissues.

3.1 The PaTienT

Prosthetic design, selection and use starts with a person who needs an artificial leg. Some are born without limb (congenital defi-ciency), others are amputated by trauma or disease. In case of the latter, the choice of amputation-level (3.1.2) is the most important for the eventual type of prosthesis and the functional outcome of use. Transtibial ampu-tations are in about 70 percent of the cases the best solution, resulting in a below-knee stump -or better – a transtibial residual limb (3.1.3).

Of course, the primary purpose of a pros-thesis is to improve the performance of func-tional activities and mobility, including ambu-lation. Some basic biomechanics of gait and of posture should be known (3.1.4 to 3.1.6).

Special user groups, children and patients with a reduced activity level, have their own design requirements. They are introduced in section 3.1.7

Muscles

Femur

Patella

Tendons(Patella T)

Tibia

Fibula

Calf Muscle

Scar

Figure3-2:Bones of the lower limb (most right), mus-cles (middle) and anatomy of the residual limb (below) [Adapted from IMT-Baghdad and Wisse et al. 2002].

Tibialis anterior

Peroneus tertius

Soleus

Gatroc-nemius

Tibials posterior

Illium

Ischium

Femur

Patella

Tibia

Fibula

Tarsal bones

Metatarsal bones

Phalanges

Tubercle

8

3.1.2 TransTibial amPUTaTions

The term trans is used when an amputation extends across the axis of a long bone. When two bones are involved, such as the tibia and fibula, the primary bone is identified. Transtibial is the proper term for a below-the-knee amputation. Amputations between bones or through a joint are referred to as disarticulations.

levels

There are different levels of transtibial ampu-tations (different types), namely short, stand-ard and long (figure 3-4). During amputation in a standard procedure, bone is cut shorter than skin and muscle, so that the skin and muscles can be folded over and the wound can be closed well (figure 3-3).

Standard transtibial amputation occurs when between 20 and 50% of the total tibial length is preserved. An elective amputation in the middle third of the tibia, regardless of measured length provides a well-padded and biomechanical sufficient lever arm. An ampu-tation shorter than 80 mm is not advised because of the resulting small-moment arm, ill-fitting of the prosthesis and the fact that it makes knee extensions difficult. Long transtibial amputations result in poor blood supply in the distal leg. The two amputations

most proximal to the transtibial are the knee-disarticulation and the Syme amputation. The Syme amputation is an ankle disarticula-tion in which the heel pad is kept for good weight bearing. See figure 3-4. Transfemoral (above-the-knee or thigh) amputations will be mentioned as well, because biomechanics and solutions for transfemoral prostheses are often comparable to transtibial amputations.

Requirements: The universal prosthesis should fit most transtibial amputations, which implies a residual tibia length of at least 80 mm to 50% of the original length.

Figure3-4:Different levels of transtibial amputa-tion [Seymour 2002].

Figure3-3:Amputation procedure [Seymour 2002].

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Prevalence

Amputation is a common medical treatment all around the world. In most developed coun-tries the amputee point prevalence (amount of amputees in one thousand residents) is about 1.55 permillage and leg amputees make up about 1.33 permillage of the population (see Appendix F for sources).

However, worldwide prevalence is much higher, about 2.44 permillage.

In all zones, transtibial amputees form about 53% of the total amputees and about 65% of all leg amputees. Calculations with these fig-ures result in table 3-1.

Yearly figures from the UK show that the percentage of lower limb amputations stay constant in the next few years. Data from the National Health Service shows that transtibial amputations account for about 50% of all 6000 yearly amputations and congenital deficiencies [UK NHS, 2005]. More figures of prevalence can be found in Appendix F.

Because transtibial is the most common level of amputation, the worldwide amount of transtibial amputees is quite high. Unfortunately, reliable figures on the amount of limbless (without a prosthesis) patients aren’t available. However, our research in Sri Lanka shows that from the 40-160K amputees (assume 80k) there, only about 10k were provided a prosthesis. At least a million limbless worldwide is very realistic assump-tion.

Project: The universal prosthesis can be used to provide European and US amputees with an addition to their healthcare program. However, to reach full potential, the project should aim to reach 1 million limbless world-wide.

3.1.3 residUal limbs

Where possible, the physicians will try to save the original limb of the patient. However, when tissue-saving techniques are no longer holding out, the practitioners will decide to amputate the patients leg. This results in a residual limb, also called residua or stump. During the operation, the fibula is cut 20 mm shorter than the tibia, so the calf muscle has enough space to form a good stump. Compare figures 3-2 and 3-4.

Residual limbs differ from patient to patient, not only in dimension, but also in skin condi-tion, flexibility and strength. [Seymour 2002, p38]. All these properties can change over time.

Zone Population TranstibialAmputees

Europe 450 M 370 K

U.S. 250 M 210 K

Worldwide 6,1 G 9,7 M

Table3-1: Amount of amputees worldwide.

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develoPmenT

During the first 4 weeks, the residual limb will significantly change in shape and prop-erties, mainly due to tissue-healing. Then, up to 6 months after the operation, the limb will shrink to its final size.

Other changes in size may occur after first 6 months. Some patients experience changes during use (every day). Also, limbs will change due to training and body-weight increase or decrease.

Finally, skin conditions such as tissue damage, scar-forming, onset of callous spots and oedema can change the shape of the skin.

Project:The universal properties of the pros-thesis can be especially useful direct after the operation (during the first 6 months). If the prosthesis can (also) be fine-tuned by the patient, it can be used to adjust for small daily shape-changes during day-to-day use (after 6 months). These adjustments should be very easy to do (few user actions). Slow, long term changes (taking weeks/months) (e.g. patient increases in weight) may be adjusted for using a tool.

measUremenT and shaPe

Measurements of the residual limb can be taken in many ways. In practice, only basic measurements are taken, because in most cases a plaster cast from the residual limb itself is used to shape interfaces of the limb with prosthetic devices (see chapter 4). Measurements are important to keep track of the changes in the stump over time, espe-cially during the first 6 months.

Common measurements are:

- Length from the tibial tubercle (or from the middle of the patellar tendon) to the end of the bone.

- Length from the tibial tubercle (or from the middle of the patellar tendon) to the end of the soft tissue.

- Circumferential measurements from 0 mm (at the tibial tubercle or at the middle of the patellar tendon) and than at every 40 mm (downwards).

These circumferential measurements are also an indication for the shape of the resid-ual limb (figure 3-5). In appendix G statistics are presented that show the measurements of residual limbs in Sri Lanka. These measure-ments give an indication of in which range the prosthesis should be adjustable. A range of 80-250 mm covers most of the amputa-tions.

Requirements: The universal prosthesis should fit all three basic residual limb shapes. Residual limb lengths of 80 to 250 mm should be fitted comfortably. Circumferences around the patellar tendon should be varied from 250 to 350 mm.

Figure3-5:Residual limb shapes: conical (a), cylindrical (b) and bulbous (c). [Seymour 2002]

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skin and TissUe condiTions

After the healing of the residual limb, most patients are left with a scar. Also skin con-ditions may vary. Patient may have several area’s and combination of the conditions mentionel in table 3-2:

Other skin complications that can occur are: abrasions (areas of skin breakdown), blisters (mostly caused by friction), contact dermatitis (inflammation), distal oedema (swelling) and skin ulcerations.

Skin areas where these complications or conditions occur, are often very sensitive to pressure or friction. These areas should not be loaded (to much) by the prosthesis.

There are more factors that indicate possible problems. A low temperature may indicate arterial insufficiency, abnormal warmth may indicate infection.

Impaired sensitivity can lead to skin damage due to the lack of feedback to the patient. On the other hand, the patient may report phan-tom pain in stead of pain with a evident phys-ical cause.

If the physician suspects blood flow problems, blood flow tests of the remaining extremity may indicate general health of blood flow. Patients with blood flow problems cannot be ignored, because most elderly amputations are the result of reduced blood flow in the extremities (often due to diabetics).

“By the year 2005, the five countries with the highest incedence of diabetes will be India, China, the United States, Pakistan and Indonesia.” [ACA 2001, p79]

Requirements: In situations were pressure or friction on certain areas will cause pain or further complications, the universal pros-thesis must be able to avoid loading these areas. The universal prosthesis should allow or stimulate blood flow in the residual limb. The socket has to make total contact with the residual limb to avoid oedema and invagina-tion.

Preconditions:The patient has a reasonable amount of loadable areas. The patient has a reasonable healthy residual limb. T

code condition explanationt) tenderness over sensitivity,

NL: overgevoeligheid

a) adherence NL: aankleving

i) invagina-tion

to fold in so that an outer becomes an inner surface, NL: kloofvorming

c) callus a thickening of or a hard thickened area on skin, NL: eelt

d) discolora-tion

reduction of health skincolor, NL: verk-leuring

(nh) nonheal-ing

NL: niet helend

Table3-2: Skin conditions.

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areas oF weighT bearing and areas oF relieF

The tissue in the residual limb is more or less suitable for transferring load in certain areas. The loadable areas can be seen in figure 3-6 .

Areas of weight bearing include:

- Patellar tendon- Flare of the medial tibial condyle and the

anteriomedial aspect of the tibial shaft- Anteriolateral aspect (pretibial group) of the

residual limb- Midshaft of the fibula- Gentle end-bearing if tolerated

Areas of relief include:

- Anterior and lateral edges of the lateral tibial condyle

- Head and distal end of the fibula- Crest and tubercle of the tibia- Anterior distal end of the tibia

In general, relief areas include bony promi-nences, areas of poor blood supply, or areas that are near prominent nerves such as the common peroneal nerve.

Requirements: The universal prosthesis should offer areas of pressure and areas of relief according to the anatomy of the resid-ual limb. In any case, load should be trans-ferred to the patellar tendon.

Preconditions: The patellar tendon, tissue medial and lateral to the tibial crest, and tissue on the posterior is loadable.

Figure3-6:Pressure tolerant and sensitive areas. Most left: A scematic of sensitive (light red) and tolerant (dark red) areas [Seymour 2002]. 4 Right: anterior, lateral, anterior and medial view of a positive (cast), with pressure sensitive (red) and tolerant areas (blue).

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Figure3-7:Base of support. The size of the base of support varies with a change in foot position. [Seymour 2002]

range oF moTion

The knee joint should allow enough move-ment to properly use the prosthesis (range of motion or ROM). Additionally, the patient needs at least the strength to move the pros-thesis. Before fitting a prosthesis, the knee is normally tested for:

- Anterior and posterior drawer- Medial and lateral (valgus and varus) stability- Crepitus (a peculiar crackling, crinkly, or grat-

ing feeling or sound under the skin or in the joints)

- Recurvatum (hyper extension of the knee)

Preconditions: The range of motion of the patient allows walking with conventional prosthesis.

3.1.4 PaTienTs PosTUre and PrinciPles For alignmenT

Posture is the alignment of the body seg-ments in space. To maintain upright posture (to stand), the body must counteract the effects of gravity or other forces acting on it. This involves muscles, ligaments, capsules and other soft tissue, bone and the nervous system.

In the case of an amputee wearing a pros-thesis that weighs less than the original limb, the centre of gravity will shift proximally and away from the prosthesis. The amputee may lean the trunk towards the uninvolved side to compensate. For the best stability the line of gravity should pass through the base of the support (see figure 3-7).

Requirements:The prosthesis should not be too light (<0.5 kg). Distal weight has more inpact on the energy consumption and expe-rienced comfort.

Prosthetic alignment is the position of a prosthetic socket in relation to foot and knee. Alignment is performed in two phases, a bench or static alignment based on estab-lished guidelines and a dynamic alignment based on the patient’s gait patterns to fine-tune the device to achieve an optimal gait pattern.

Static alignment is the alignment of the socket and foot. The physician uses a plumb line from the centre of the posterior wall of the socket to a location about 10 mm lat-eral to the centre of the heel. This alignment maintains a fairly normal base of support and loads the more-pressure-tolerant areas on the medial residual limb rather than the fibular head region. In the sagittal plane, a plumb line should fall from the centre of the lateral wall of the socket to just anterior to the front edge of the heel (figure 3-8).

Figure3-8:Static alignment for a transtibial pros-thesis. A) In the frontal plane, B) In the sagittal plane. [Seymour 2002]

center of gravity

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Static alignment of the transtibial socket usually includes 5 to 10 degrees of flexion of the socket. A residual limb in a socket with vertical walls would easily slide up and down. Also, flexion allows greater exposure of the patellar tendon for weight bearing (figure 3-9 and figure 3-10).

Requirements: Alignment of the prosthesis should allow more load to the medial resid-ual limb rather than the fibular head region. Alignment allows 5 to 10 degrees of flexion of the knee (and the socket).The patellar tendon should be loaded most.

A well dynamic aligned prosthesis will not rotate while standing, due to the equilib-rium between the ground forces and the forces from the residual limb on the prosthe-sis. However, during gait the forces are not along the same line and the fit of the socket becomes crucial to resist the rotation during gait.

Subjects seem to find a PTB socket omst comfortable with a PTB-bar at 4 mm depth [kim 2003]. Furhtermore, according to Besser [1992] 45% of the total body weight can be carried by the Patellar Tendon.

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Figure3-9:Inclination of the bulge of the PTB (see section 4.2) socket. The bulge provides more surface for weight bearing than the wall of the socket. Note the relatively longer horizontal component of the vector. [Seymour 2002]

Figure3-10:Forces on the patellar tendon increase because of the need to compensate moments due to distance a and b and because the inclination of the force factor on the patellar tendon [Wisse et al .2002]

Gravitational Forceof Body-Weight

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Figure3-11:Alignment of the transtibial pros-thesis in the sagittal plane, placing the foot medial to the socket. This placement tends to cause a rota-tion of the socket that then places pressure on the proximal medial and distal lateral residual limb. [Seymour 2002]

Figure3-12:Alignment in the sagittal plane placing the foot lateral to the socket, resulting in pressure on the fibular head and distal medial residual limb. [Seymour 2002]

Figure3-13:Alignment in the frontal plane. Left: normal. Right: Foot placed to far backward, causing pressure on the distal anterior part and proxi-mal posterior part of the limb.

Figure3-14:Alignment in the frontal plane. Left: normal. Right: Foot placed to far forward. If the force though the spocket fell posterior to the ground reaction force vector, the prosthesis would tend to rotate.

Also, the line of gravity of the prosthetic limb should run near or through the (knee) joint, because otherwise the body must com-pensate the resulting moments with muscle activity. This is mostly achieved by linear alignment. Figures 3-11 to 3-14 show linear alignment (in contrast to angular alignment) problems and their resulting forces.

Requirements. Rotational alignment of the prosthesis should result in a minimum of rotational forces while standing, while pro-viding enough rotational support during gait. The line of gravity of the prosthetic limb should run through the knee joint. This might imply the need for linear alignment.

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3.1.5 basic biomechanics oF gaiT

Terms

For an explanation of the terms used to describe the type of motion, rotary motions (such as flexion/extension, abduction/adduc-tion, etc), the planes in the body (frontal or coronal, horizontal or transverse and sagittal) and biomechanical concepts (such as axes of joint motion, instant axis of rotation, kin-ematic chain, degrees of freedom), etc, I refer to standard reference books and figure 3-15.

Gait or ambulation can be defined as the translation of the body from one point to another by way of bipedal motion (NL: gang, pas, loop). In both walking and running there is a rhythmic displacement of body parts that maintains the person in constant forward progression.

Normal gait is not easily defined. Therefore, literature sometimes speaks of accept-able gait. From a mechanical perspective, it would seem logical to take energy efficiency and force transmission as main criteria, but in practise a naturally looking gait is most important. Overall the amputee should exhibit even step length, step timing and arm swing. Walking speed is less important (also see section 5.5).

Requirements: The prosthesis should allow acceptable gait.

Figure3-15:Planes of the body. [Seymour 2002]

Period Phase DescriptionStance Initial contact When the foot hits the ground

Loading Until the opposite foot leaves the ground

Midstance Until the body is over and just ahead of the support

Terminal stance To toe-off

Preswing Just after heel-off to toe-off

Swing Initial swing Until maximum knee flexion occurs

Midswing Until the tibia is vertical

Terminal swing Until initial contact

Table3-3. Phases in gait. [Seymour 2002]

Figure3-16:Distance variables of giat. a) left step length, b) left stride length, c) right stride length, d) right step length, e) width of base support f) Right toe-out, g) left toe-out [Seymour 2002]

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initialcontact

loadingresponse

mid-stance

terminalstance

prewsing initialswing

mid-swing

terminalswing

%ofgaitcylce

0-2 0-10 10-30 30-50 50-60 60-73 73-87 87-100

rockerphase

Heel rocker

Ankle rocker

Ankle rocker

Forefoot rocker

kneemoment

extension; valgus

flexion; valgus

flexion to extension

extension extension to flexion

gravity extend-ing; accelra-tion

gravity linear distract-ing

gravity flexing; decelera-tion

kneeangle

0 0-15 flexion

15-5 flexion

5-0 flexion

0-30 flexion

to 60 flexion

to 30 flexion

0

anklemoment

plantar-flexion; valgus

plantar-flexion; valgus

plantar-flexion todiorsi-flexion

dorsiflex-ion

dorsiflex-ion

gravity plantar-flexing



ankleangle

neutral 0-15 plantar-flexion

15 planter-flexion to 10 dorsi-flexion

0-5 dorsiflex-ion

0-20 planter-flexion

10 plantar-flexion

neutral neutral

Table3-4: Phases of the gait cycle of the right leg. [Adjusted from Seymour 2002]

Gait can be described from both a kinematic and kinetic standpoint.

kinemaTics

Kinematics is the classification and compari-son of motions. In gait, the feet are moved in different phases (table 3-3).

In figure 3-16 the different distance vari-ables, occurring during the gait phases, can be seen.

To provide adequate weight acceptance, single-limb support and limb advancement, the hip, knee, ankle and subtalar joints need to flex and rotate. Their range of motion (excursions) accompanying the phases of gait can be found in table 3-4.

Apart from joint mobility other factors can affect normal gait. Among these are age, strength, cardiovascular status, habit, cloth-ing, psychological status (including fear of falling) and factors that affect the location of the centre of gravity (COG) of the total body.

Preconditions: The joint excursions during normal gait are the minimum required range of motion that is also needed for proper gait with the prosthesis.

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kineTics

Kinetics is the branch of mechanics that is concerned with the forces that cause motions. The primary external forces acting on the body in normal gait are gravity and the ground reaction force. Muscles function to counteract these forces and to accomplish the forward progression of the body.

During gait the COG moves side-to-side. Placing the feet further apart, thus creating a wider base of support increases stability, but results in an increase in the side-to-side excursion of the COG and thus an increase in energy cost.

The ankle/foot complex plays a very impor-tant role in limiting the vertical excursion of the COG. A greater excursion will increase the energy required for gait.

At initial contact (see table 3-3), the critical event for normal gait is that the heel should contact the floor first. Once the foot hits the ground, loading response occurs. In this phase knee flexion and plantarflexion occur for shock absorption. Hereafter, stability is of utmost importance. Especially during ter-minal stance, the gastrocsoleus contracts to stabilize the advancing tibial and to raise the heel (heel-off phase). During swing the mus-cles of the anterior compartment prevent the toes to drag on the ground. In midswing, the

knee passively extends with relaxation of the knee flexors.

Requirements: The prosthesis should allow enough stability with a lateral feet placement which resembles normal gait.

Requirements:The energy-cost of use of the universal prosthesis should be comparable to current prostheses. The ankle-foot complex should decrease the vertical excursion of the centre of gravity. The prosthesis should be light.

Requirements: During swing, the toes may not hit the ground.

Figure3-17:Gait deviations to accommodate a long limb. A) Hip hiking, B) Lateral trunk lean, C) Circumduction, D) Vaulting, E) Excessive hip and knee flexion. [Seymour 2002]

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3.1.6 gaiT deviaTions

Gait deviations are often the result of a ill-fitted or poorly aligned prosthesis. Other common and often related causes include: muscle weakness, deformity (of bone or soft tissue), impaired control including sensory loss, pain, fear or anxiety.

Weakness of the residual limb with poor muscle tone can result in rotation of the soft tissue and of the prosthesis itself over the underlying bone. It can also increase pres-sure.

A common deformity is a leg length differ-ence. Either the leg consisting of a residual limb and prosthesis or the other side is to long. This can be caused by the prosthesis itself (pylon to long), or by insufficient flexion in the knee (or in the hip). Whatever the cause, it is more difficult to clear the ground during swing. An individual has several options to accommodate the long limb (Figure 3-17). An additional option to accommodate is a wide walking base, but walking this way is very energy inefficient.

With impaired sensory control in transtibial amputees, the ability to know when the feet are in contact with the floor and to know where the joints are in space is lost. A person with an amputation must rely on the sensory input from the residual limb, a factor that may affect the individual’s confidence in gait. As a result, the walking speed (cadence) of individuals with amputations is lower than normal.

Fear and anxiety are particular pertinent contributors to gait deviations among those with amputations. Vaulting may occur if there is a fear of stubbing the toe of the pros-thesis during swing. If there is a lack of con-fidence in the prosthesis, the individual may try to get off the limb quickly, resulting in an uneven step length.

Pain can develop from the stress and strain of the device on the tissues of the body and can cause major gait deviations. The natu-ral response to pain is to try to move away from it, to take the weight or pressure off the painful area. For example, an individual with pain of the distal residual limb may bend the trunk laterally to get more weight of the area. [Seymour 2002, p109-13]

Requirements: The length of the universal prosthesis should be adjustable. The pros-thesis must provide enough and direct sen-sory information to the residual limb. The prosthesis should be easily trusted (win the patients confidence), especially during gait. Pain, especially from to much stress or strain in the tissues of the residual limb, should be avoided.

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3.1.7 sPecial User groUPs; children and PaTienTs wiTh a redUced acTiviTy level

There are several special patient groups, that can benefit from a universal prosthesis.

Project:These special user groups are being reviewed to see later on if the specific require-ments they have for the prosthesis can give the Universal Prosthesis an edge over current existing systems for these groups

children

Children need a new prosthesis every six months. The universal prosthesis could improve their comfort, because changes in stump size are more often adjusted for. While the load during stance is lower (lower body weight) their life-style if often very active (many loading cycles). Children are very demanding and impatient users, the prosthe-sis should be even more easy to use than in the case of adult patients. The standard range of sizes the universal prosthesis would be usable for might not be sufficient. A smaller version may be needed.

PaTienTs wiTh a redUced acTiviTy level

Inactive, often elder patients are sometimes bound to their beds. If their prognosis is not bright, the practitioners might decide not to make a prosthesis (due to costs). These people could benefit from the universal pros-thesis. The load during stance is standard, but the load cycles and total usage time are much less.

With these patients, the donning and doff-ing should be very easy. Also, extra attention to the blood flow in the residual limb should be given.

Requirements: Design requirements may vary for these special target groups.

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3.2 The ProsTheTisT and oTher Team members in a ProsTheTic clinic

Team aPProach

Considering the amputation as an accom-plished fact, a whole team of experts is needed to provide optimal rehabilitation of a patient. The team should include the physi-cian, prosthetist, orthotist, physical and occu-pational therapist, vocational rehabilitation counsellor, social worker, psychologist, rec-reation therapist, dietician, nurse, the patient and the patient’s family or support network. The key to any team is communication. The patient should be regarded as the team leader and have clear expectations of the rehabilita-tion process.

ProcedUres oF a ProsTheTic clinic

The procedures of a prosthetic clinic are out-lined in figure 3-18. The better the prosthesis assists several of these procedures, the more successful it will be.

The ProsTheTisT

In this project, the prosthetist receives spe-cial attention, because he or she is the team member who is most in contact with prosthe-ses. In general, the prosthetist’s function is to design, fabricate and fit prostheses.

Knowledge and Education: To select, fit or train an individual in the use of a prosthe-sis, a practitioner must posses a basic under-standing of biomechanical principles, normal alignment, movement and forces acting on the body or body segment. In addition, an understanding of normal gait and common gait deviations is important. Prosthetics is a profession that combines specialized clinical and technical skills.

Professionals are educated in these subjects and may be certified as either an orthotist, a prosthetist, or both.

Prosthetist may own their own business as a sole proprietor or work as an employee in a hospital, rehabilitation centre, research facil-ity, or private business.

Pre-Prescription Examination

Prescription

Pre-Fitting Intervention

Prosthetic Fabrication

Initial Check-out / Examination

Prosthetic Training

Final Check-out or Examination

Vocational Training

Placement

Return to Existing Employment

On the Job Training

or

or

Figure3-18: Procedures of a prostetic clinic [Adapted from Seymour 2002]

Thesalesoftheindustry 2000 2002 2003 2004National 100 106 110 112Foreign 100 102 103 104Total 100 103 105 106

Theuseofresourcesandhalf-fabricates From National 100 103 105 108

Foreign (import) 100 97 93 94Total 100 99 97 99

Table3-5: Grow indexes of the sales in the medical equipment industry in the Netherlands [CBS 2005].

SellsofprostheticdevicesinNetherlands

2001 2002 2003

(Million Euros) 57 85 80

Table3-6: Market for prostheitc devices in the Netherlands [CBS 2005].

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3.3 ProdUcer oF ProsTheses

In contrast with e.g. shoe manufacturers, who sell a complete product direct to the end-user, the manufacturers of prostheses sell system components and materials to the prosthetist, who fabricates the final product for the patient.

Big producers of prosthetic components include Össur, Otto-bock and Endolite. A (more) complete list of producers can be found in appendix I.

3.3.1 dUTch indUsTry

Industry figures show a healthy grow in the Dutch medical equipment industry (Table 3-5). Also, specific figures about the revenues show a healthy industry (Table 3-5).

Industry statistics about the production of medical equipment and instruments, ortho-pedic devices, prosthesis and precision instruments. Dutch product price industry index figures can be found in table 3-6 [CBS 2005].

The Dutch industry is a relatively big importer of medical devices: 2015 million US$ in 1996. The Netherlands only imported 30% from the EU, but this is most likely due to the status of the Netherlands as a leading European

import/export centre [IEEE 1998].

3.3.2 worldwide indUsTry

In 1996, the World market for medical devices was estimated at US$ 94340 Million, of which 15.5% is within the orthopedic and prosthetic product sector (= 14717 Million) [IEE 1998]

Over 90% of the world market for medi-cal devices and supplies consists of the regions USA (42%), Europe (28%), Japan and Australia.

In the Western European market (1996), big players are France (17%), Germany (32%), Italy (10%) and The UK (11%). The Netherlands only make up for 4,7% of the market. In the European market, the orthopedic and pros-thetic product category is a bit bigger: 18.5% [IEE 1998]

Total import to Western European countries of other artificial body parts than artificial teeth (dentistry) and orthopedic implants was worth about 600 million US$.

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3.3.3. comPonenT and FiTTing Prices

The costs for fitting a prosthesis to a usercanvarywideandisdependentofmanyfac-torssuchas:

- currency rates, - place / country,- hour costs /salary- machnines and tools needed- facility needed- etc, etc

Togive some indication, the numbers fromthe studybyD.Datta et al [2004]areused.Theycomparedthecost,timaandfunctionaloutcome implications for changing fromPTBtoICEXsockets.Thesecommonlyusedsocketsystemsaredescribedinchapter4.

They calculated the following costs (inEuros):

COSTSFACTOR ICEX PTBProsthesistssalary 27 39

Technicianssalary 7 49

Transportationofthepatient

44 88

Componentcosts 1100 300

TOTAL 1180 476

However,ithastobenotedthattheycalcu-latedwithanhourprice for thetechniciansand the prosthetists of 22Euros. It is clearthatthiscalculationiswithoutmachinecosts,facilitationcosts,etcetc.

The needed times where as follows (min-utes):

TIMENEEDED ICEX PTBProsthesists 75 105

Technicians 25 180

TOTAL 100 285

With an more realistic man/machine hourpiceof100Eurosthiswouldleadtothefol-lowingcosts:

COSTSFACTOR ICEX PTBProsthesistssalary 125 175

Technicianssalary 42 300

Transportationofthepatient

44 88

Componentcosts 1100 300

TOTAL 1311 863

Andtheprice-differenceismuchless.

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4 transtibiaLProstheses

Theprosthesisisadevicewithperhapsthemost important function in the total careafteranamputation.Itrestoressomeofthelostfunctionsoftheamputatedlimb.Todoso,itwill(1)suspendthelimb(weightbear-ing), (2) give thepatient stability (balance),(3)allowanacceptablegait(ambulation),(4)prevent further deformations of the bodyand (5) provide some sociopsychologicalsupport (cosmetics) for the patient. Thechoiceofprostheticdesignisthereforeverydependent on the patient’s rehabilitationstageandprognosis(section4.1).

Almost all current prostheses are build-up from pre-fabricated components and acustom-made socket (4.2). The fabricationsupplies, inorthopaedicsoftencalledmate-rials,andthecomponentsareboughtfromprostheticdevicemanufacturersandassem-bled by the prosthetist. Generally, compo-nents (4.3)offeredbydifferentmanufactur-ers don’t differmuch, because their shape,function and properties are dictated bybiomechanics(4.4)andtheanatomyoftheirusers. Components and professional careare not cheap, but social services enablemostWesternpatients to acquire the rightprosthesis(4.5).

Componentscomeintoexistence inthefac-tory and are assembled into a prosthesisby the prosthetists. Because of wear andchanges in the patients situation, the pros-thesissometimesneedtoberepaired(4.6).

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4.1 TyPes according To The PaTienTs rehabiliTaTion sTage

Therearethreetypesofprostheses(interim,temporary and definite) each appropriatefor different stages after amputation. Thesestages can be determined by the health ofthewoundandthedressingthatthewoundneeds to heal. A clear definition is difficult.In practise, the period in which a certainprosthetictypecanbeusedoverlapsseveralrehabilitationstages.Table4-1givesanover-view.

In this section descriptions of these pros-thesic types are given. While many terms are employed, the designs that are used in the early stages following amputation (in this report referred to as interim prostheses) are very similar in function.

Other terms used for Interim Prosthesis include (common abbreviations are added in brackets):

- Immediate Postoperative Prosthesis (IPOP)- Early Postoperative Prosthesis (EPOP)- Immediate postoperative prosthetic fittings

(IPPF)- Custom Removable IPOP- Weight Bearing Rigid Dressing (WRD)- Removable Rigid Dressing (RRD)- Post Surgical Prosthesis (PSP)- Removable Protective Socket (RPS)- Protective Prosthesis- Early Fitting Prosthetic Socket- Early Ambulatory Prosthesis- Early Rehabilitation Prosthesis- Adjustable Postoperative Protective and

Preparatory System (APOPPS) – FLO-Tech.- Initial Prosthesis

The prosthesis that is used for gait training is in almost all literature referred to as the temporary prosthesis. Terms which also refer to temporary prostheses are:

- Universal Prosthesis- Prefabricated Prosthesis (PFP) - Preparatory Prosthesis

The prosthesis that the patient will use finally is called the definite or permanent prosthesis.

Startuseaftersur- Usedtill(aftersurgery) Prosthesistype/CompressionDirect 1months(woundsheal) Softandsemi-rigiddressings0to1weeks 1months(incisionheals) Rigiddressinginterim,partial

loadpossible

5to21days 3months(incisionandsutureshealed)

Rigiddressinginterim,completeloadingpossible

10to21days 6months(residualshapealmoststable)

RemovableProtectiveinterim,compressionneededduringuse

1to3months 6months(residualshapestabilizes) Temporary,compressionduringnight

3to6months Prosthesiswearsout Definitive

Table4-1: An overview of clinical patient stage and applicable prosthesis type. In practise, the choice is less time dependent, but is determined by the healing rate and activity level of the amputee.

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Figure4-1:Fabrication of a RRD and Custom Removable IPOP. Left: 3 spandex socks, pads and an attachment plate, 3 velcro straps and attachment base plates. Middle: fiberglass cast with cut lines and base plate attachment points and the result. Inset: anterior and posterior sec-tions of the cast with gel pads. Right: Ambulation is possible, with weightbearing limited to 10-20 kg. [Walsh 2003]

4.1.1 removable rigid dressing - rrd

The removable rigid dressing is a form of a dressing (also see section 5.1 for prepros-thetic care), which can be used very soon after the operation. The problem with rigid dress-ings is that the wounds cannot be inspected and attended to. A removable setup solves this problem. The Removable Rigid Dressing with integrated components for amublation is called an custom removable IPOP. In contrast with a conventional IPOP, it can be applied before the patients’ incisions are closed (and the sutures healed). Full load on the risidual limb is not possible till the wound is closed fully. Removable rigid dressings are always made by the prosthetist. The procedure includes making a rigid dressing, cutting it open along specific lines and applying Velcro bands (See figure 4-1). The materials needed are standard and easily available.

Advantages:Very early load on the residual limb, while wound inspection is still possible. It offers protection and access. Pre-ambula-tory training is possible (limited load), An early start with patient education can be made.

Disadvantage:Time consuming to make and fit and highly skilled personnel needed.

There are no commercial packages that offer a complete solution including a rigid dressing and ambulation components.

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Disadvantage:High skilled personnel needed. Wound inspection is difficult.

Some companies sell universal IPOPs based on air compression. These prostheses exist of a universal outer socket and insertable air-cells. An example can be seen in figure 4-3.

4.1.2 immediaTe PosT oPeraTive ProsThesis - iPoP

An IPOP (see figure 4-2) is a combination of a rigid dressing, a pylon and a foot. It was developed in the late 60s. An IPOP is used while the residual limb still changes shape fast, but the incision of the operation is healed and the sutures removed.

In the first place, an IPOP can provide the psychological and physiologic benefits attrib-uted to walking soon after the amputation. The early use of an IPOP is attributed many other advantages to the patient (although not by all researchers), but (because fabri-cation is time consuming and not easy), the IPOP is little used. IPOPs are made by the prosthetists in the hospital. While the orig-inal design is based on a plaster cast (rigid dressing), a fibreglass cast can also be used to reduce weight.

Advantages: Control and shaping of the residual limb, protection of the surgical site, improving healing time, maintenance of resid-ual and sound limb and upper body strength, reduction of contracture development, main-tenance of cardiovascular status, early return to balance and ambulation, social and emo-tional support, shorter hospital stay, shorter overall recovery time, quicker identifications of the patients functional levels [Seymour 2002, p128].

These inflatable IPOPs are far less time consuming to apply to the patient and are used in many Dutch revalidation hospitals. However, the residual limb must be healed fully, the inflatable IPOP cannot be used too long and the weight distribution cannot be controlled. Therefore the inflatable IPOP cannot be applied to all patients.

Figure4-3:The universal IPOP (Aircast Air-limb) is inflatable to accomodate differ-ent stump sizes. [source: ACA 2001,

Figure4-2:A complete IPOP (without pylon). [Source: Seattle Rehab Research, US Veteran Affairs]

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4.1.3 removable ProTecTive sockeT - rPs

If a (rigid) dressing is no longer needed, but the residual limb still needs to be formed through compression, a com-pression device (see section 5.1) can be used in conjuncture with a removable protective socket. This socket is used for patients with very easily damaged residual limbs. Weight bearing toler-ance is gradually build, to enable the patient to wear a firm definite prosthe-sis later [Seymour 2002, p138]. Over this custom-fitted device a Universal Frame Outer Socket (UFOS) can be put to enable weight bearing (See figure 4-4).

Advantages: The residual limb is well protected to additional trauma. The pres-sure and weight bearing tolerance of the residual limb is gradually improved. The socket and the Universal Frame Outer Socket can be easily adjusted to accom-modate each patient. Easy access for hygiene.

Disadvantage: Sockets custom made, expensive.

Flo-tech also provides pre-fabricated protec-tive sockets (APPOP-system). Their system exists of a flexible outer socket which allows gentle reduction of the socket’s overall cir-cumference. The mid-thigh design prevents knee flexion contractures. The Velcro bands help to shape the residual limb (see figure 4-4).

The Flow-Tech UFOS (Universal Frame Outer Socket ), also fits over the VCSPS (Variable Circumference Supra Patellar Preparatory Socket), together forming a complete pre-paratory system to fit 80% of the transtibial amputations. [Source: flow-tech brochures]

Disadvantage:Many sizes needed, expensive.

Figure4-4: The Flow-tech Adjustable Postoperative Protective and Preparatory System (APPOPS) provides a prefabricated prosthetic system offering protection, con-trolled shaping of the residuum and early rehabilitation. The TOR (top left) is a prefabricated socket (available in 22 sizes) that fits over elastic wrapping and bandages. The socket prevents knee contraction and provides pro-tection for the residual limb. When fitted with a UFOS (universal frame outer socket, middle) it functions as an interim prosthesis (top right). Full load and knee flexion becomes possible with the VCSPS (bottom). Fitted with a UFOS the VCSPS (available in 34 sizes) can be used as a temporary prosthesis. [Source: Flow-tech Brochures]

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4.1.4 TemPorary ProsThesis

The temporary prosthesis is a socket, pylon and foot system which is used when the patient wounds are fully healed, while the residual limb still changes its shape fast and the socket needs to be replaced several times as the volume of the residual limb stabilizes. The temporary prosthesis came into exist-ence in the 1970s, together with the develop-ment of the endoskeletal design (See section 4.2), which made the use of adjustable align-ment components possible. It provides the same functions as a definite prosthesis, but the alignment can be adjusted more easily by the prosthetist to improve the patient’s gait. The patient can use the temporary prosthesis at home. However, in most cases the tempo-rary prosthesis is not yet fitted with an opti-mal foot and additions such as a rotator or shock-absorber (see section 4.3.5). Also, aes-thetically the prosthesis is not finished yet (e.g. no cosmetic cover) and the temporary prosthesis could be heavier than a definite.

Advantages: Better control over the align-ment for the prosthetists, the socket needs to be fabricated several times.

Disadvantage:The system might be heavier, not all components can be fitted, the prosthe-sis lacks cosmetics.

The preparatory socket is normally created by using a plaster mould of the residual limb as a template ( just as with definite prostheses, compare figure 4-8). The other components, such as the pylon and the foot, are stand-ard available. In most cases, a SACH foot is used (see section 4.3.3). The connective com-ponents, such as the interface between the socket and the pylon, can be easily rotated. The alignment of the prosthesis is deter-mined by the angle between the socket, pylon and foot.

Most companies offer a wide range of temporary components, because after the dynamic gait training the temporary parts will be replaced by definite components (of the same company). Also, many definite com-ponents can be adjusted quick enough to be suitable for a temporary prosthesis, such as the connective devices from Endolite (see figure 4-4 and section 4.3.5).

Some systems are said to be usable as interim and temporary prosthesis, such as the Maramed components (figure 4-5).

Figure4-5:Connective part between socket and pylon, which can be used in tempo-rary and definite prostheses. [Source: Endolite brochure]

Figure4-6:Components of Maramed orho-pedic Systems. Left: X-tender system can be used as a temporary prosthesis(middle). At the right a retainer is shown, in which a custum-made socket can be attached. [Source: Maramed website]

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4.1.5 deFiniTe ProsThesis

The definite prosthesis is the prosthesis that the patient will use in daily life. In most cases, it highly resembles the temporary prosthesis, now finished with a cosmetic cover or pros-thetic skin (see section 4.3.5). The definite socket is difficult to adjust. When the residual limb changes in shape or pressure sensitivity, a new socket is needed.

Advantages: Firm fit and therefore the best gait and control over the prosthesis. Cosmetics are pleasing.

Disadvantage:Difficult to adjust.

The definite prosthesis is always fabricated by the prosthetists. However, there is a wide range of available materials and production methods. The choice of these have a great impact on weight (composites are very light), adjustability (thermoforming plastics can still be somewhat adjusted after fabrication by applying local heat) and comfort. An interest-ing commercial material is ICEX from Össur which consists of carbon fibre enhanced sheets that harden when mixed with water (see figure 4-7). The ICEX is one of the few systems which can be fabricated directly onto the residual limb.

Normally, a plaster cast is made from the residual limb, of which in turn a positive cast is formed. This cast is then adjusted (see sec-tion 4.3.1) and the final socket is then fabri-cated by either vacuum thermoforming or applying epoxy resins (plastic lamination). (See figure 4-8).

Figure4-7:The ICEX toolbox and component box. [Source: Ossur website]

Figure4-8:Standard fabrication starts with taking a negative mold. Then plas-ter is poured into the negative mold to create a positive mold. At last, the positive mold is shaped by the prosthetist to emphasis the shape. The final socket is made by laminat-ing or thermoforming it around the positive. [Seymour 2002, p179]

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4.2 sTrUcTUral designs There are two solutions for the structural build-up of a prosthesis: the exoskeletal design, which is around for a long time and the endoskeletal or modular design, invented in 1970 (compare Appendix E). Nowadays, the endoskeletal design is by far the most common.

4.2.1 exoskeleTal sTrUcTUre

An exoskeletal structure has a hard outer cover made of plastic laminate (figure 4-9). Socket and pylon are integrated into one product. Sometimes, the foot is a standard component, such as in the case of the Jaipur prosthesis (see figure 4-10), but it can also be integrated (figure 4-9).

The structure consists of soft foam con-toured to match the other limb with a hard laminated shell.

Advantages: High strength, better suited for occupations that require great durability, such as farming or construction work. Better resistant against dirt. Sometimes also better heat resistant.

Disadvantages: Alignment and replacement are difficult. Difficult to fabricate. Flexion, shock-absorption and rotation is absent in the rigid prosthesis.

Vision:An integration of the socket and the pylon, while allowing for adjustability, could result in a highly durable and resistant pros-thesis.

Figure4-10:The Jaipur prosthesis, here drying from paint finish, consists of a exoskeletal structure with a separate manufactured foot. [Source: FINS- Sri Lanka]

Figure4-9:The exoskeletal prosthesis (depicting socket, plastic exterior and foot) is one, integrated product. [Seymour 2002]

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4.2.2 endoskeleTal sTrUcTUre

In an endoskeletal design, a pylon is used to transfer forces from the residual limb to the floor. The endoskeletal or modular prosthesis is build from components. The basic compo-nents of an endoskeletal prosthesis (figure 4-11) are the socket (4.3.1), the pylon (4.3.2) and the terminal device (4.3.3) (almost always referred to as the foot). Every prostetic design needs suspension (4.3.4) to stay put when the leg is lifted. Sometimes additional compo-nents (4.3.5) are included such as a rotator, shock-absorbers, a sock or (gel-) liner, a cover or a prosthetic skin.

Advantages: Being adjustable, being light-weight, this setup is cost efficient when com-ponents need to be replaced, the (mass-pro-duced) components are of relatively low costs. The total system is highly customizable to the patient’s needs.

Disadvantages: Not so strong, components may be expensive, custom-made socket needed.

Vision:The universal prosthesis will be really successful when the socket and the pylon can be used together with a wide range of (already available) feet.

A combination of socket and pylon, while maintaining the endoskeletal principles is called a monolithic socket and pylon combi-nation and may be attached to commercially available prosthetic feet. One thermoplastic design is the Endoflex [Valenti, 1991]. See figure 4-12 for an example without cosmetic cover. It is suitable for a majority of amputees and its advantages include increased flex-ibility, absorption of stress and shear and reduced cost.

Vision:An integration of the socket and the pylon, while allowing for adjustability, could result in a highly durable and resistant pros-thesis.Figure4-11:The endoskeletal prosthesis always

contains a pylon. Very seldom the other parts are integrated. Normally, the socket and foot are modular com-ponents. [Seymour 2002]

Figure4-12:The 4C Air Lite Monolithic (above 2 pictures show manufacturing steps. A carbon-fibre sock is one of the important materials) and the Endoflex (lower pictures) are two of the few designs in which the pylon and socket are integrated. [4C Air-Lite Tech Manual, Valenti 1991]

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4.3 comPonenTs

Components for the endoskeletal prosthesis are widely available. This section offers an overview.

4.3.1 basic comPonenTs: sockeT

The socket is the connection between the residual limb and the prosthesis. It must not only protect the residual limb but also trans-mit the forces associated with standing and ambulation.

Sockets are generally created by using a plaster mould of the residual limb as a tem-plate. Some prosthetic manufacturing facili-ties use computer-assisted technology to “map” the residual limb and then manufacture a socket directly from that data (CAD-CAM fabrication).

There are primarily two socket designs used for transtibial amputations, the patellar tendon bearing (PTB) and the total surface bearing (TSB). Since the late 50’s, the PTB socket has been the design of choice for most traumatic transtibial amputees [VHI 2002].

Project:The definite socket is in practically every case custom made and therefore the most challenging part for a complete univer-sal prosthesis. Therefore this project must focus on the socket and its effects on the patient and the prosthetist.

Vision:The universal prosthesis will be really successful when the interface with the body is as comfortable as current sockets.

rigidiTy

There are different types of hardness for the socket. Again, there is a multitude of terms in use and definitions are unclear:

- liner- soft socket or softsocket- semi-rigid socket- Flexible socket- Hard outer, soft inner socket system- Hard socket

Traditionally, the socket is constructed as hard as possible, because this rigid type of sockets transfer the forces well to the pylon and gives control to the patient. However, since the invention of the liner, a new devel-opment is the hard outer, soft inner socket (semi-rigid sockets). These sockets consist of a shell and a liner that are both formed to the residual limb. The outer sockets func-tion is protection of the residual limb and the transfer of forces. The outer socket sur-rounds the liner, made of a flexible material (in most cases Pelite, a poly-ethylene foam). This socket helps with the better distribu-tion of forces. The difference between a soft socket and a conventional liner [see section 4.3.5] is that the liner is a hollow, stretch-able, standard tube, while the soft socket is fabricated to the shape of the residual limb of the patient. Soft sockets are more often used for transfemoral amputees than for transtibial amputees. Also, for transfemoral amputees there is a system that integrates hard elements (ISNY concept, figure 4-13 and 4-14) with flexible (polyurethane) parts into one socket. However, this socket type is only recently developed at Össur [2002] and infor-mation about development of a transtibial type is limited [COTA 2002].

Project:Recent developments in softsockets for transfemoral amputees, seem to suggest that a flexible socket could be well adapted to transtibial prosthetics.

Figure4-13:ISNY Components [Source: Website Otto-Bock]

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recTiFicaTion

There are two principles for force distribu-tions between the residual limb and the pros-thetic socket. The first, “Rectified” takes in account which areas and tissues are less sen-sitive to pressure and the socket puts more pressure there. The second, “Unrectified” does not take the difference in tissue in account and the socket is fabricated such that it dis-tributes the forces of the residual limb best distributed as possible (in most cases except the distal end). Interesting, there is little liter-ature that compares these two types of pres-sure distribution. However, recent studies do suggest that unrectified sockets perform just as well as rectified sockets. Rectified sock-ets tend to be evaluated better in less active situations, while unrectified sockets are more comfortable during heavy use. [Weeks 2003]

On the other hand, prosthetists at LIVIT (Den Haag) suggested that unrectified sockets tend to rotate around the residual limb and thus offer problems when subjected to tor-sion. Also, they mentioned that rectification (while years ago being quite exaggerated) is practically not so strongly emphasized any-more in the socket fabrication.

PaTellar Tendon bearing (PTb) sockeT

The PTB socket is the best known rectified socket design. The PTB socket offers areas of pressure and areas of relief in accordance with figure 3-6 from section 3.1.3. As can be seen, important pressure bearing areas are the patellar tendon, the medial tibial flare (next to the tibial crest) and the posterior of the residual limb. The socket makes contact with the residual limb even in areas where no pressure is transferred, including the distal end, to avoid pockets of oedema.

Requirements: The universal socket should make contact with all areas of the residual limb, to avoid pockets of oedema.

Figure4-14:Flexible ischial-containment socket for transfemoral amputees (this one from Otto-Bock, inset from Hanger) consist of a flexible inside and a frame. Other names include Total Flexible Brim, the ISNY and SFS (Scandinavian Flexible Socket)[Seymour 2002].

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ToTal sUrFace bearing (Tsb) sockeT

The TSB socket design is an unrectified design, that was developed in the mid 1980’s. It provides complete contact of the prosthetic socket to the residual limb with no built-in pockets for relief of bones and other sensi-tive tissue. By allowing total surface contact, all tissue of the residual limb is in contact with the prosthetic socket, thus reducing the loading on the medial tibial flare and patel-lar tendon. When using this type of design it is usually necessary to use a roll-on type of liner made of silicone, mineral gel or similar material. The thickness of these liners is usu-ally three, six or nine millimetres. This design is fast becoming the socket design of choice for traumatic amputees. [VHI 2002]

Requirements:The socket can either transfer pressure equally or rectified, as long as the total area over which the pressure is distrib-uted is optimized.

PlUg FiT sockeT

The plug fit prosthesis, mostly used for trans-femoral amputations, was very popular from WWI to mid 1950’s, but is seldom used today. The socket shape is a simple cone (figure 4-15). Transtibially, this socket design provided weight bearing at the patellar tendon and was used in conjunction with a thigh lacer for suspension (see section 4.3.4). Additionally by tightening the thigh lacer additional weight bearing was transferred to the thigh. The distal end of the prosthesis is usu-ally left open with no distal wieght bearing. [VHI 2002]

hydrosTaTic sockeT

The Hydrostatic socket is a socket that is unrectified, but in stead of determining its shape from the shape of the unloaded resid-ual limb, it is formed around the (hydrostatic) loaded limb. This socket type is very com-fortable while standing, because pressure distribution is optimal [SOURCE]. However, when soft tissue is hydrostatically loaded, it becomes more round shap round shaped. This may cause friction and instability when the prosthesis is subject to rotation or torque.

Figure4-15:Plug fit socket. The first prosthetic socket without weight-bearing at the distal end by Verduin 1696 [Wetz 2000]

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The before mentioned ICEX socket (figure 4-7, figure 4-16) is produced on the residual limb. It is cast under pressure with a pressure-cast-ing device. Due to this production method, it is a hydrostatic socket design. All pressure is distributed equally, but areas still be relieved from pressure by applying pressure pads.

4.3.2 basic comPonenTs: Pylon

The pylon is a tube or shell that attaches the socket to the terminal device. The main func-tion of the pylon, is to transfer force from the socket to the ground. Pylons have progressed from simple static shells to dynamic devices that allow axial rotation and absorb, store and release energy.

Because of the high forces involved, most pylons are made from titanium. For geriatric purposes (less use and low weight) some-times aluminium is needed. Plastic pylons are used in designs meant for the third world, such as the ICRC-limb (figure 4-17) (polypro-pylene) and monolithic prostheses (see figure 4-12). In these cases, an addition exoskeletal can be applied after alignment, to enhance the durability of the prosthesis.

Also, there are low cost systems with mul-tiple pylons, however these seem to be only used in Argentina (about 2000 produced in 1989, see figure 4-18).

New types of pylons are slightly flexible and take-over some of the functions of the ankle (figure 4-19).

Pylons can be orderd in standard sizes or sawn into the needed length by the prosthetist.

Figure4-18:(left) Trimodular Pylon as used in the sauer-bruck trimodular physi-ological prosthesis [Angarami 1989]

Figure4-17:The ICRC-limb makes use of a poly-propylene pylon.. Its cross-section is H-shaped.

Figure4-19:(right) Springlite Advantage DP flex-ible pylon and dynamic response foot by Hanger Orthopedic Group. [Source: website]

Figure4-16:Icex finished socket (left). Pressure pads are added to compensate for weight intolerant areas (cutt-through right) [Source: Ossur Icex brochures.]

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4.3.3 basic comPonenTs: FooT/ankle sysTem

The foot is the typical form of the terminal device, but it may take other forms for water or sports activities, or for use as an interim-prosthesis. The main function of the foot is to aid in gait and provide aesthetics.

Better defined the functions of the prosthetic foot are (1) to provide a stable weight-bearing surface, (2) to absorb shock, (3) to replace lost muscle function, (4) to replicate the anatomic joint, and (5) to restore cosmetic appearance.

The ankle function usually is incorporated into the terminal device. Separate ankle joints can be beneficial in heavy-duty indus-trial work or in sports such as mountain climbing, swimming, and rowing. However, the additional weight requires more energy expenditure and more limb strength to control the additional motion.

Because of the biomechanical and anatomi-cal parallel, designers often speak of the foot-ankle system. Prosthetic feet are broadly classified as energy-storing feet and non–energy-storing feet.

non-energy-sToring FeeT

Rocker“foot”: The rocker is the most simple terminal device. It does not try to resemble a normal foot, but is a stump end, which allows a very nice ambulation. This terminal device is most useful in interim prostheses.

SACH foot: Solid Ankle Cushion Heel – Developed in the 1950s, the SACH foot is the simplest foot. It mimics ankle plantar flexion, which allows for a smooth gait. There are no moving parts, which makes this design very durable and ideal for children and for individ-uals whose ambulation is limited to walking (sedentary patients).

The SACH foot designs allow compression of the foam heel at heel-strike to simulate planter-flexion. A wooden internal keel pro-vides stability in mid-stance and allows for a relatively easy rollover in late stance. [VHI 2002]

SAFEfoot: Solid Ankle Flexible Endoskeleton – This in 1980s developed foot is more flex-ible than the SACH foot. This design had an elastic keel, which enabled a smoother and easier rollover, which is more preferable than the rigid keel of the SACH foot. Some disad-vantages include limited push-off, increased cost and added weight. [VHI 2002].

Figure4-21:SACH foot (Adapted from Seymour 2002]

Figure4-22:SAFE II foot. (Original manufacturer is Campbell Childs Inc, now bought by 4C (Foresee Orthopeadic Products)).

Figure4-20:Left: Principle of Rocker foot or sole. [Adapted from: www.customfootware.com] Right: Low cost prosthesis with cane pylon and rocker foot 37

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Single-Axisfoot: Predating the 1860s, single axis feet contain an ankle joint that adds pas-sive plantar flexion and dorsiflexion, which increase stability during stance phase. Single-Axis feet pre-date the American Civil War and still are used today on a limited basis. The main advantage is that the foot will allow for a quick foot-flat, which increases knee stabil-ity in an above-knee prosthetic wearer or in a below-knee prosthetic wearer who uses a thigh corset with knee joints in early stance. This feature is important in the individual who has knee instability. Disadvantages include weight, maintenance, abrupt dorsi-flexion stop, noise and cost. [VHI 2002]

Multiple-Axisfoot: The multiaxial foot adds inversion-eversion and transverse rotation capabilities to the function of the single-axis foot and is often recommended to accommo-date uneven terrain. Its weight and mainte-nance requirements are similar to that of the single-axis foot and is a good choice for the individual with a minimal-to-moderate activ-ity level. [VHI 2002]

simPle energy sToring

STEN foot: The STored ENergy foot is a simple energy storing foot that has a keel that compresses in the loading response to mid-stance of gait, thereby storing energy. The energy is released in the terminal stance to the preswing phase of gait. [Seymour 2002]

Figure4-24:Multiple axis foot. [Seymour 2002]Figure4-25:STEN foot. [Source: Kinsley

Manufacturing Co brochure]Figure4-23:Single-axis foot. [Seymour 2002]

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dynamic resPonse: Dynamic Response (formerly known as advanced Energy Storing) feet have a plastic spring keel that provide a dynamic respon-siveness during stance. There are numerous dynamic response feet available, such as the Carbon Copy, Seattle, Flex-foot, Springlite,etc (figure 4-26, 4-27). The more aggressive ambulator can use these designs, including runners and those participating in recrea-tional or competitive sports who can load the forefoot for these activities. Disadvantages include increased fabrication time and increased cost for some designs. [VHI 2002]

Hybrid Design feet (figure 4-28) are avail-able that combine multiaxial ankle mecha-nism with dynamic response, such as the College Park foot/ankle and the Phoenix foot. These designs can be used for recreational and competitive sports, as well as for uneven terrain. Disadvantages would include mainte-nance and cost. [VHI 2002]

Figure4-26:(Above) Though from the outside not visible, energy storing feet differ from the inside [Impulse foot, OHIO Willow Wood] Various energy-stor-ing feet. Earch foot is composed of a compressible heel and a flexible keel spring. A) Seattle foot, B) Dynamic foot, C) STEN foot, D) SAFE foot, E) Carbon Copy II foot. [Hafner et al. 2002]

Figure4-27:Advanced energy-storing prostheses: A) Modular III, B) Reflex VSP, C) Advanced DP, D) Pathfinder. [Hafner et al. 2002]

Figure4-28:Two hybrids: The Seattle Cadence HP [Source: Seattle website] and the MICA Genisis II+. [Source: MICA web-site]

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4.3.4 basic comPonenTs: sUsPension

Prostheses can be attached to the residual limb by a variety of belts, wedges, straps, suc-tion, or a combination of the above. Designs include differential pressure suspension sys-tems, anatomical suspension systems, strap suspension, thigh corset with mechanical hinges, Silesian Belt and pelvic joint with belt.

Most important transtibial suspension meth-ods:

1) Supracondylar Cuff – A supracondylar cuff, affixed to a socket, allows the prosthesis to hang from the top of the knee (Anatomical suspension). In Dutch often referred to as the KBM design.

2) Jointandthighcorset – This suspension method bears much of the patient’s weight on the thigh. (corset suspension)

3) Waist belt suspension – In this design, much of the weight of the prosthesis is dis-tributed around the waist (corset suspension).

4) Sleeve suspension – An elastic or neo-prene sleeve is pulled over both the prosthe-sis and a large area of skin, thereby suspend-ing the prosthesis by partial suction (suction suspension).

5) Gel linerwithshuttle-lock – One of the more advanced designs, this pin, incorporated at the end of the liner, fits into a shuttle-lock-ing mechanism fabricated into the bottom of the socket. (suction suspension). The liner is equipted with a pin or plunger threaded into the distal end. This pin can lock into the socket. to remove the prostesis, a button on the locking mechanism is depressed.

anaTomical sUsPension

Anatomical suspension designs (figure 29) are the second most desirable option for suspension of the prosthesis. Suspension is achieved by careful contouring of the socket walls over and proximal to the femoral epi-condyles to lock the condyles in place. This method of suspension is known as supra-condylar (SC, In Dutch often referred to as the Kondyl Bettung Munster, KBM) and can be very effective in suspending the prosthe-sis and in providing enhanced mediolateral stability in individuals with a shorter residual limb.

A variant to this design allows for moulding of the socket anteriorly above the patella for added suspension and to control hyperexten-sion in the shorter residual limb. This design is known as supracondylar/suprapatellar (SC/SP), sometimes referred to as the Patellar Tendon Suspension (PTS). [VHI, 2002]

Advantages:Are increased medial-lateral sta-bility with the SC and increased anterior-pos-terior stability with the SP feature.

Disadvantages: include localized pressure over condyles and restriction of full flexion.

Figure4-29:(right) Anatomical Suspension. The supracondylar suspension is in this case removable due to the brim. (right, middle) The supracondylar suprapattelar system is fixed. [Seymour 2002]

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sTraPs

When it is not feasible to use differential pressure or anatomical modes of suspen-sion, a strap (figure 4-30) can be used to sus-pend the prosthesis. A popular strap, called a PTB or supracondylar cuff, is attached to the medial and lateral walls of the prosthesis at their posterior-proximal juncture and is then angled proximally over the patella. The lower border of the cuff touches the superior border of the patella to achieve suspension. In addi-tion to the cuff, a waist belt with extension assist can be attached to the proximal border of the cuff to increase suspension and to

assist the individual in extending the prosthesis. [VHI, 2002]

Advantages: This design can accommodate changes in volume and is relatively simple to adjust.

Disadvantages: Include slight pistoning and belt irritation.

corseTs

The thigh corset (figure 4-31) with mechani-cal hinges was the design of choice up until the early 1960’s. [VHI, 2002] Also, a corset can be worn around the waist.

Nowadays, there are to much disadvantages in comparison to the other suspension meth-ods to use corsets for definite prostheses, but they are still used in conjuncture with a interim or temporary prosthesis.

Advantages: In using the thigh lacer with joints include the reduction of weight bearing on the residual limb and can greatly increase the medial-lateral stability.

Disadvantages: Include pistoning, added weight and bulk, difficul-ties in donning and exces-sive wear and tear on clothing.

sUcTion sUsPension

Suction suspension uses an atmospheric pressure (vacuum) or suction to maintain the prosthesis onto the residuum. Suction suspension is broken down into 2 categories: standard suction and silicon suspension suc-tion. A standard suction is simply a form-fit-ting rigid or semi-rigid socket into which the residual limb is fitted. The silicon suction uses a silicon-based sock, liner or sleeve (also see section 4.3.5) that slips onto the residual limb, which is then inserted into the socket. The silicon helps to form an airtight seal that stabilizes the prosthesis. [VHI 2002]

Advantages: These designs tend to provide the amputee with enhanced function, great-est range of motion, added sense of security, greater control of prosthesis and no piston action when fitted properly. Of all suspension modes, suction designs tend to be the most desirable because of the enhanced retention of the prosthesis to the residual limb created by the vacuum.

Figure4-30:The PTB cuff or supracondylar cuff. [Seymour 2002]

Figure4-31:The thigh corset can be used in conjuncture with a waist belt and an elastic strap. [Seymour 2002]. The suspension sleeve has a similar work-ing principle (left) [Otto Bock].

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Several suction suspension designs are used [VHI, 2002]:

1) One design incorporates an overall snug fit with a valve placed distally into the prosthetic socket. The skin is in direct contact with the socket interface. In order to use this type of suspension, the residual limb has to be stable with no fluctuations in volume and generally free of scars that could prevent vacuum from being achieved

2) Another system includes the use of elas-tomer sleeves made of silicone, urethane or mineral gel. (Figure 4-32) These sleeves are rolled onto the residual and have a distal pin attachment (plunger) that anchors dis-tally into the socket locking the prosthesis.

in place. These systems allow for moderate volume changes by placing socks of varying plies on the outside of the sleeve to achieve a snug fit. Also, applica-tion for residual limbs that may have some scarring or grafts is possible.

3) Variants to these methods include the “hypobaric” design, which has a valve dis-tally in the socket to expel air and a silicone rubber band (gasket) moulded into standard textile stump liners at the proximal socket. This gasket is positioned slightly distal to the socket edge, which creates a seal and maintains vacuum or suction. This silicone band is moulded into prosthetic sheaths and stump socks of varying plies to accommodate volume changes. Sometimes, to enhance the seal, a skin lotion is used for a wet fit.

4) Another design allows a mineral gel sleeve to be rolled onto the residual limb, with a fabric backing and no distal pin. (Figure 4-33) Once the sleeve has been placed onto the residua, the residua is placed into the socket, where a distal valve expels the air. With all the air expelled, a second sleeve is placed over the inner mineral gel sleeve and outer socket, sealing any air from entering the socket, thus creating a suction or vacuum. This design can accommodate some volume changes by use of a thicker sleeve.

5) The simplest design of achieving suc-tion suspension could be to use a rubber-ized sleeve over the outer socket surface and onto the mid-thigh, thus preventing air from entering into the socket. This design allows for stump socks and/or soft insert to be used.

Figure4-32:Pin/Shuttle suspension. [Seymour 2002]

Figure4-33:Mineral gel sleeve suction suspen-sion. [www.customprosthetics.com].

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4.3.5 addiTional comPonenTs

liners and socks

Liners (figure 4-34) fit inside prosthetic sockets and are used to cushion and protect fragile limbs and to accommodate volume changes. They can be used to suspend pros-theses by rolling them onto a residual limb to provide suction suspension or they can have wedges built into them to provide supra-condylar suspension. They can be made of silicone, urethane, and mineral gel, rubbers and expanded polyethylene foam. The thick-ness of liners is usually three, six or nine mil-limetres and this thickness is referred to as a ply. [VHI 2002]

- Stockinet (tubular open ended cotton of nylon material)

- Sleeves- Compressors- Shrinkers (Elastic Wraps or compression sock)- Socks (not only for the feet!, wool of cotton)- Liners- Gel sheath

roTaTors and shock-absorbing sysTems

The Torque Absorber (figure 4-35) allows the leg to rotate with reference to the socket during stance phase, automatically returning the leg to the normal position during swing phase. The torque absorber is excellent in activities where rotation is important: golfing, dancing, bowling, base-ball, standing and working at a bench for considerable periods of time. Generally, the shorter the residual limb, the greater the loss of natural torsional capabilities. A torsion absorber would restore the loss of torsion.

Shock absorbing pylons allow for telescoping of the pylon to absorb shock to the residual limb that occurs in jumping and running activities, as well as aggressive walking.

coUPlers, locks, valves and grace PlaTes

All basic components are connected by spe-cific components. These connective compon-vents (figure 4-36) often exist of a “male”and a “female”part, that can be attached in a range of angles. These angles determine the alignment. The connective component that is integrated with the socket is called the grace plate.

In case of suction suspension, valves need to be added. Locks are needed for above-knee prostheses.

Figure4-34:Double/Single Socket Gel Liner [Silipos].

Figure4-35:Demountable Torque absorber and its effects. [adapted from endolite]

Figure4-36:Some examples of connective com-ponents [adapted from www.atlas-ti.com]

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covers and ProsTheTic skins

Most endoskeletal setups are finished with a cosmetic cover. This cover usually exists of a foam inner part and is finished with a very flexible “sock”. In very expensive prostheses, the outer sock can resemble the remain-ing limb, including hairs, veins, etc. then the cover is called a prosthetic skin. Some manu-factures speak of skin coatings. (figure 4-37)

4.3.6 maTerials & Tools

Plastics, supplies, tools, alignment systems, they are the resource for the prosthetist (figure 4-38).

Figure4-37:Prosthetic skins can have a high life-like appearance [left, dorset and orthopeadic]. Uflate sleeve skin covers shrinks to fit the prosthesis when treated with a heat-gun.

Figure4-38:Examples of supplies (above): Rivits, Polyester Resin-Laminae, box of stockinettes, pneumatic cast cutter, carbon tape [Fillauer Supplies bro-chure]. Static alignment is done on an alignment table [otto bock[. Supplies enable prosthetists to make custom liners [otto bock].

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4.4 biomechanics oF TransTibial ProsTheses

Now the structure of prostheses and the used components are discussed, a applica-tion of biomechanics on the residual-limb-prosthesis system is useful. From this analy-ses important criteria and insight why the endoskeletal structure is so popular can be derived. Again kinematics and kinetics are considered (compare sections 3.1.5 and 3.1.6). Both have implications for the selec-tion, fit, use and design of prosthetic devices. Generally, kinematic considerations provide insight into the alignment of the prosthe-sis, while kinetic considerations will provide insight in the design requirements.

kinemaTics

Orientationofaxesofmotion: For the total limb to move in its normal path of motion (figure 4-39), the axes of the human joint and the prosthetic orientation must be aligned similarly. The choice of the type and location of the axes will affect the movement and sta-bility of the prosthetic limb. [Seymour 2002, p78]. For example, a dynamic ankle joint can improve ambulation on rough terrain, but reduces the stability of the prosthetic limb.

Requirements: The universal prosthesis should be normally aligned similar to the axis of motion of the knee. Enhanced flex-ibility and additional joints (such as a flexible pylon) could be applied, but stability is more important.

Range of motion: The prosthetic device should allow normal range of motion in any plane, which for a transtibial prosthesis involves primarily the rotation of the knee and ankle in the sagittal plane.

However, because of the closed kinematic chain (the foot stands on the ground), adja-cent joints are likely to be effected. For example, when a prosthetic foot is locked in plantarflexion it will result in an abnormal knee angle (FIG 4-40). [Seymour 2002, p79]. This is an important observation, because for example an abnormal knee angle could result from a problem in the foot/ankle system.

Requirements: The universal prosthetic system should include hints when it is aligned well.

Figure4-40:Limited dorsiflexion at the ankle. If the ankle can not dorsiflex normally, either A) the individual will weight bear on the toe or B) the knee must hyperextend to get the foot flat on the ground. [Seymour 2002]

Figure4-39:Pathway of the instant axis of rota-tion for the knee joint. [Seymour 2002]

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Degrees of freedom: If the prosthesis has a different number of degrees of freedom as the normal joint, the function of the joint will be affected. For example, some prosthetic feet, such as SACH feet, allow plantar- and dorsi-flexion, but do not allow pronation/supination. This will affect the interface of the foot with the ground. Adaptation to uneven terrain is diminished and forces may be transferred to the residual limb. [Seymour 2002, p79]

kineTics Stress: Stress or pressure considerations lead to a preference of a large surface to bear forces. A typical application of this principle is the use of a total surface-bearing (TSB) socket [See section 4.3.1]. High pressure on the tissue of the residual limb could occlude the vessels, creating ischemia (oxygen short-age) and tissue damage. Also, nerves are pressure sensitive, resulting in pain or nerve damage. [Seymour 2002, p80]

Deformation: Tissues of the residual limb as well as materials used in prosthetics, vary in their stiffness (their ability to resist deformation). In the residual limb, the stiffer bone bears the brunt of the load, but is also more pain-sensitive to pressure. These con-siderations lead to designs such as the patel-lar tendon bearing (PTB) socket [See section 4.3.1] as shown in figure 4-41. All considera-

tions for the size and location of suspensions should take in account the relationship of force area, stress toleration and deformation. [Seymour 2002, p80]. Deformation of the tissue also occurs while the residual stump is loaded. Therefore, the shape during load can be different from the unloaded shape. Especially in hydrostatic socket, semi-rigid and softsocket designs this can be a problem. Under evenly distributed pressure, the soft tissues tend form a cylinder or cone. If this happens, the system will find it difficult to transfer torque (cylinder in cylinder). A solu-tion is using a somewhat triangular socket.

Requirements:the socket design should con-sider rotational forces, while the residual limb is loaded.

Figure4-41:Stress on the residual limb from the prosthesis. A) The hypothetical situation in which the residual limb is of uniform firmness and the socket matches the circular shape of the limb. B) A residual limb of nonuniform firmness and a socket that matches the circular shape of the limb. This would result in increased stress on the firm areas of the residual limb. C) The same residual limb with a socket designed to equalize the pressures over the firm and soft areas. D) The same socket design used to accommodate pressure-sensitive areas and pressure-toler-ant areas. [Adapted from Seymour 2002]

Equal stess (pressure) throughout

Increased stess

Decreased stress

ReliefStress

(pressure) equilized

throughout

Relief

Build up Build up

A B C D

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Elasticity: Tissue should not be loaded beyond the yield point, which would result in permanent deformity. The same principle applies to materials used in the prosthetic design. The material characteristics such as yield strength and ductility affect their usage in the fabrication of prosthetic devices. [Seymour 2002, p82]

The materials used in the components of the prosthesis may cause or solve gait deviations. They will affect deformation and the energy deformed of returned, wit a result impact on gait. In transtibial conventional prosthesis, this principle is mostly used in shock-absorb-ing feet (compare table 4-2, first row). The socket and pylon are generally designed as stiff as possible.

Table4-2: Gait deviations due to materials and the alignment [Seymour 2002]. Note that many align-ment choices can have the same effect. If the effect is unwanted, all can be adjusted, but some will cause other problems (because one alignment choice will have multiple effects).

AreaandProblem Effect

heelcushiontoo hard

- foot rotation - execssive knee flexion

too soft- foot-slap- absent or insufficient knee flexion

Displacementofthekeelposterior - early knee flexion (drop-off)anterior - delayed knee flexion

Excessiveflexionofthepros-theticfoot

dorsiflexion- excessive knee flexion- early knee flexion (drop-off)

plantarflexion- absent or insufficient knee flexion- delayed knee flexion- circumduction

Excessiveplacementofthefootinrelationtothesocket

medial - excessive lateral thrust of prosthesis

anterior- absent or insufficient knee flexion- delayed knee flexion

posterior- excessive knee flexion- early knee flexion (drop-off)

Excessivetiltofthesocketposterior - delayed knee flexion

anterior- early knee flexion (drop-off)- excessive knee flexion

Socketfitstoo loosely

- foot rotation- pistoning

too tightly - reduced knee flexion/exention

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Strain: Some materials exhibit a differ-ent stress/strain curve for increasing and decreasing stress, called hysteresis. Materials which can dissipate a lot of energy, such as vulcanised rubber, can be used to absorb energy. These materials will be selected for either their return energy or absorption of energy. Important here is that one material would not work for all individuals, because the load or stress placed on the material would be different from, for example a light individual and a heavy individual. A case in point would be the firmer heel of a SACH (see section 4.3.3) prosthetic foot for a heavier individual. [Seymour 2002, p83]

Tension, compression and torsion forces play an important part in the design of the pylon.

Shear forces: The application of a shear or tangential force can cause shear stress and strain on weight-bearing surfaces, for exam-ple, in a poorly fitted prosthetic device. Soft tissue in general should not be loaded with shear force. [Seymour 2002, p84]

Bending forces: The patellar tendon bear-ing prosthesis is in principle a three-point system, resulting in bigger forces than one would expect purely from the patients weight (see figure 4-42).

Viscoelasticity: Viscoelastic materials, such as the connective tissues of the body, exhibit some of the characteristics of both elasticity and viscosity. Viscous substances have the ability to resist loads that produce shear. Viscoelastic materials may be used in prosthetics to reduce shear and pressure, as can be seen in liners (often containing ure-thane) (see section 4.3.5). Viscoelastic mate-rials demonstrate the characteristic of creep, the increase in strain with time under a con-stant load. Constant loading, subjects joints, surrounding structures and the prosthesis itself to the effects of creep. Deformation of the residual limb or of the prosthesis will be the result. [Seymour 2002, p88]

Figure4-42: Bending forces on the residual limb while standing. [Wisse et al. 2002]

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4.5 Financial issUes & disTribUTion

Of course, the prosthesis and its components are not fabricated freely. For every prosthetic design that becomes a success, benefits to the patient (such as improved comfort), the prac-titioner (such as reduced fabrication time), the producer (higher revenues or bigger market share) and to governmental institutions such as assurances (a clear solution with a good prognosis for a fair price) should be out-weighing the costs.

All transtibial components are part of a com-plex value chain (figure 4-43).

Project: In the value chain, the universal prosthetic system can be regarded as a spe-cific component.

4.5.1 To The PaTienT

Most prostheses are reimbursed by in assur-ances, but reimbursement rates may vary widely. Usually an insurance company will pay for a new prosthesis every 3-5 years or sooner in cases of ill-fitting caused, for exam-ple, by weight gain or loss.

The cost of a prosthesis varies widely depend-ing on the degree of disability, activity needs of the wearer, and the types of components and materials used. The cost of a transtibial prosthesis ranges from $4,000 to $16,000 [Seymour 2002, p49], including components, materials, labour, office visits and adjust-ments (in the first 90 days).

In Western countries the assurances will reimburse the more cheaper prostheses ($4000). The fight for reimbursement of more expensive components can be difficult and the improvement in functionality for the patient should be very clear.

In developing countries, the patient will have to pay for the prosthesis themselves, or their “social insurance” will be provided by humanitarian aid organisations, such as US-Aid. Normally, a transtibial prosthesis can be provided between $60 and $100. $100 seems to be the “magic border” for the amount most NGO’s are willing to pay for prosthetic help. These costs include components, materials, labour, office visits and adjustments in the first weeks. However, long-term aftercare is generally unavailable until the time a patient really needs a new prosthesis.

Project: The universal could cut back total cost, because of the reduced need of office visits and adjustments.

Figure4-43: A Simple model of the value chain of prostheses. Value is increased from left to right. Note that some companies have multiple roles.

Party Raw Resources

Materials producer

Components producer

Distributor

Productexample

Carbon, Oil Sheets Feet System

Companyexample

Shell GE Plastics

Otto-Bock Otto-Bock LIVIT Jan Klaas

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4.5.2 To The PracTiTioner

The most valuable resource to the prosthetist is time. He needs this time not only to fit and fabricate the prosthesis, but also for meetings with other members of the team and to adjust prosthesis for patients in their rehabilitation.

Project:The universal prosthesis could allow the prosthetist to cut back costs (time) or to improve his service to the patients.

4.5.3 To The ProdUcer

Because of the high requirements to the components (light, durability, etc), they can be quite expensive. The customer (the prosthetist) will suggest them to the insur-ance company or the patient as long as the benefit to the end user is clear (and that depends highly on the patients level of activ-ity).

Project: The producer could improve his market share, while maintaining his profit-revenue ratio, especially in the niche for products between temporary and definite prosthesis.

4.5.4 To governmenTal insTiTUTions

Insurances primarily look for solutions, not for the final price of the product. That is , they assess what the functional needs are of

the patient and how they will develop in time. Then they select the most price efficient solu-tion over a longer period.

Project: Even a more expensive universal prosthesis could in many cases be selected by the social insurances, because it will still function when the residual limb changes shape. Costs of maintenance and adjustments are decreased, especially when the patient can adjust (some aspects of) the prosthesis himself.

4.6 rePair and liFe-Time

Just as shoes, a prosthesis has a limited life-time. A study done in the United Kingdom found that on average, a new prosthesis was needed every two years.

In some cases, the prosthesis can be repaired. In the same UK study, one major repair was needed every 5 years and two minor repairs were needed per year.

Requirements.The Universal Prosthesis has a lifetime comparable with normal shoes, 1 a 2 years.

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TU Delft, 20055 LiFewithaProsthesis-theamPutee’sPersPective

For a succesful design, insight into the expe-riences of the recently amputated is needed. From a patient’s perspective, the news that a leg or arm needs to be amputated can be shocking and comes with a lot of emotions and questions. In this chapter an overview of actions that a (new) amputee has to take is given.

Recommended reading: For additional information, the First Step guide from the Amputee Coalition of America is very useful. [ACA 2001]

The patient will experience a sequence of happenings as mentioned in table 5.1.

All these situations will require sociopsy-chological adjustment of the patient and a lot of effort to learn how to use the prosthe-sis. However, life is not care-free. Some major concerns of users of prostheses are summa-rized in section 5.6.

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Phase Discription SeeSection

Theaccidentorthedisease

In a case of trauma the patient has to deal with the accident. Treatment is acute. In case of disease, such as diabetics (vascular), the patient has time to prepare for the amputation. He consults a practisioner and makes the decision (or hearing the annoucement that he needs) to be amputed.

Hospitalization During the period of surgery to provide the patient with a clean and useable residual limb.

Preprostheticcareandrehabilitation

Shrinking of the residual limb with compressive wrap-pings. Physiotherapy to prevent contractures. Fit of a temporal prosthesis as a training to use and life with a prosthesis. The residual limb reaches final shape.

section 5.1

Definiteprosthesis The choice and fit of the prosthesis is based on the assessed functionality and the amputees life-style.

section 5.2

Dynamicalignment Further rehabilitation and adjusting the alignment of the prosthesis.

section 5.3

Learning(dailyroutine).

Learning to maintain, don, dof and use the prosthesis. section 5.4

Rebuildinglife Rebuiling his or hers life after a long period of rehabili-tation. Best results with the help of a rehabilitation and aftercare team .

section 5.5

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5.1 PreProsTheTic care

After the surgery (the incision is healed and the sutures removed), a patient will need a compression device to contain residual limb oedema and to accomodate the shaping of the residual limb. Learning the patient to apply the compression device themselves is an important part of early rehabilitation. Most patients will need to wear a compression device during the night indefinitely because of oedema fluctuations. In the preprosthetic phase, compression devices should be worn 24 hours a day and reapplied about every 4 hours. Several types of compression devices are possible such as:

- Elastic wraps (Bandages): Elastic wraps are strips of elastic fabric, which are wrapped around the residual limb. 50% of the patients will be able to wrap the elastic bandages themselves, but this is a difficult practice. Wraps are readily available and inexpensive, they promote a tapered shape to the residual limb (see figure 5-1).

- Shrinkers: Shrinkers are preformed elastic “socks”. Shrinkers are easier to use, but are also more expensive. Because of the difficulty of applying wraps around the hip, shrinkers are very often used for transfemoral ampu-tations. Shrinkers can only be used after sutures are removed.

- Removable protective socket: This socket is often used with elastic wraps or shrinkers. The socket is a custom-fitted device made of

During the first weeks after an amputation, the psychological effect is the most severe. The patient will become conscious of the con-sequences of his amputation and the changes that will become evident in his life. To emphasize the fact that the patient can stay highly independent with the use of a pros-thesis, an interim prosthesis is very useful. Also rehabilitation will start very soon. Pysiotherapy will prefend contractures and muscles need to be used to stay in shape. The sooner a patient is out of hospitalization, the cheaper his treatment becomes.

thermoplastics. It protects the wound from traumatic impact, shapes the residual limb and adjusts to volume changes in the residual limb (see also chapter 4.1.2).

Figure5-1: Figure-8 wrap for the transtibial amputation: [Seymour 2002] A. First wrap max extend from proxi-mal medial to distal lateral. B. Second wrap may extend from proximal lateral to distal medial. C. Thrid wrap may overlie first wrap. D. Bandage is looslely wrapped approximately 60 milimeter to the knee. E. Completed wrap.

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5.2 selecTing The aid Having seen the huge amount of available prostheses, it is clear that the choice of pros-thesis is vital to the successrate of prosthetic use. However, the patient is not aquintanced with all the available brands and systems. He will partly have to trust the prosthetist with his selection of the type of prosthesis. But, because of differnt finances (the approval of reimbursement of more expensive prosthe-ses by social insurances can take months) patients will have to make some decisions themselves. The first decision for the patient is to buy a temporal prosthesis or a definite. (Temporal can cost more, but can also save money, because adjustments are easier). The second most imporant choice is which type of socket and in the third place comes the com-ponents, most important being the foot. Most patients will start with a decent but relatively simple temporal prosthesis. Later, especially when the patient’s prosthesis is not perform-ing to expectations, he will look for other solutions himself.

sUccess criTeria in clinical decision making

When the amputation is a fact, the first decision to make is to fit the patient with a prosthesis at all, or if his functioning will be better by providing other solutions (such as a wheelchair). This is an important decision made by the prosthetic team in close col-laboration with the patient and has to take many factors on account, including available finances. Most important functional require-ments of the patient to fit a prosthesis are sufficient trunk control, good upper body strength, static and dynamic balance and adequate posture. Once these basic require-ments are met, then

consideraTions For ProsTheTic TyPe

Once these basic requirements are met, a prosthesis can be provided to the patient. Stability, ease of movement, energy efficiency, and the appearance of a natural gait are key elements to achieve with prosthetic use. Considerations that influence the choice of type of prosthesis are:

- What is the amputation level? - What is the expected function of the prosthe-

sis? - What is the cognitive function of the patient? - What is the patient’s vocation (desk job vs.

manual labour)? - What are the patient’s avocational interests

(e.g., hobbies)? - What is the cosmetic importance of the pros-

thesis? - What are the patient’s financial resources (e.g.,

medical insurance, worker’s compensation)?

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FacTors in oUTcome oF ProsTheTic Use

If the chosen prosthesis is provided, the patient has, from a functional perspective, a proper prosthesis. However, there are more criteria for a successful outcome of prosthetic use:

- motivation individual- team approach- comfortable to wear- easy to don (put on) and doff (take off)- lightweight and durable- cosmetically pleasing- low maintenance requirements- function mechanically satisfactory

As will become evident in section 5.4, in many cases, the factors don’t add up, and the prosthesis is not used properly or not used at all.

5.3 alignmenT and rehabiliTaTion

Now the type of prosthesis is chosen, a tem-porary prosthesis can be provided to begin gait training and to determine the right fit and alignment.

Static alignment (see 3.1.4) is done on fore-hand and is primary dependent on the patient’s atonomy and posture.

Dynamic alignment needs to be done in gait. However, the patient needs to learn how to walk properly with the prosthesis (e.g. with enough confidence). His muscles need to be trained to accommodate for the higher energy requirements of ambulation with a prosthesis.

Adjustment of the dynamic alignment and the patient learning how to ambulate is a cyclic process and can take months. For the patient, who’s energy is already used to heal the wounds of the trauma and the amputa-tion, the rehabilitation is very tiring. That constricts the available time per day the patient can practise. Also, the forming resid-ual limb is still sensitive and needs to get used to the high pressures of prosthetic gait (again constricting practise time). And the shape of the residual limb is not optimal yet. For example, oedema could make the residual limb more round, therefore rotational resist-ance is reduced, while the alignment and fit are right in principle. It is the experience of the prosthetist to determine where the prob-lem lies (in the prosthesis or in the patient) and what can be done about it.

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5.4 daily roUTine: donning, doFFing and gaiT

After the hospitalization and rehabilitation period, the patient will go home. His level of functional ability, will determine the things he can do with his prosthesis and thus his “daily routine”. Most actions however, will be comparable for the majority of patients. In a way, it is very comparable with wearing shoes:

- Daily care for the residual limb- Daily care for the prosthesis - Donning: inner sockets, liners and socks, then

outer sockets (and components)- Wearing the prosthesis during activities

(ambulation, work, sitting, etc)- Changing the prosthesis?- Doffing: removing the prosthesis- Applying a compression device (see section

5.1).

daily care For The residUal limb and The ProsThesis

The wet environment in the sockets com-bined with socks, inserts, and shrinkers may cause fungi and bacteria. Proper, daily care is needed. If there are problems, it might be necessary to temporarily pause using the prosthesis. Daily healthcare, such as washing and drying of the residual limb, the socket and socks or liners, will prevent most trou-bles. Shrinkers and socks should be changed more frequently during the day in humid, hot weather. If needed, a 2-liter bottle may be inserted to restore the shape.

The inside of the socket should be cleansed weekly, washed with warm water and mild soap and dried thoroughly [Seymour 2002, p141]. It needs to be inspected daily for cracks or rough areas.

Amputees don’t need to shave their residual limb. Shaving can cause ingrown hairs, and often leads to infected hair follicles.

Requirements: The socket should be wash-able.

donning and doFFing

It is important that the residual limb and the interfaces are clean, before the prosthesis is donned, because hairs and other small par-ticles can cause pressure concentration and become a source of skin problems.

Prosthetic socks are often worn over the residual limb, because they add cushioning, reduce friction and replace lost volume in the socket due to shrinking of the residual limb. As the residual limb size changes socks can be added and removed. Prosthetic socks are available in various thicknesses often called ply.

Wearing the fewest number of socks to achieve the desired ply will help reduce bunching and wrinkling of the socks.

Liners in most cases are rolled onto the residual limb, just like a condom is. This method prevents pre-stretching of skin by donning and ensures a tight fit between the liner and the residual limb. Applying a liner can sometimes be difficult. The liner needs to have the right orientation and the application of the liner requires some force.

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Sockets are donned in different matters, often dependent on the suspension system (see section 4.3). In some cases, the amputee wears only the hard socket and the prosthe-sis can be shoved right on the residual limb. In most cases however, users use a donning sock. A donningsock is a stockinette, without a end (a long tube). It is protruded through a hole at the distal end of the prosthesis. By pulling that sock, the residual limb is pulled in the prosthesis. In case of an amputee using a liner with a pin/shuttle lock, or a liner with suction suspension, the donning sock often can not be used (of course, there are systems in which the patient can pull the end of the donning sock through the valve). Also, the donning of (hard) sockets can be a problem with patients with a very bulbous residual limb shape.

Shoes are often changeable. Of course, most persons wearing a prosthesis, also wear shoes, so that the artificial and the unaf-fected limb are harmonically clad.

changing The ProsThesis For sPecial acTiviTies

Some special activities, such as shower-ing and all kind of sportsactivities (biking, skiing, swimming), require specialized prostheses, specifically made for that purpose. An example is the shower-limb (figure 5-2). In these cases, the requirements for the prosthetic design differ.

And for some activities the prosthesis is not needed at all. Many amputees, especially kids, like to move in-house without their prosthe-sis (instead using a wheelchair or nothing).

exercise is The key

The prosthesis is (has to become) part of everyday life. All successful use of prosthe-ses starts with the amputee. As Jon Holmes states it [ACA 2001, p84]: “The most impor-tant part of the prosthesis is the motor’’. And the motor is the amputee. Good functionality and control over the prosthesis is obtained by daily exercise. Keeping the muscles and joints in shape and keeping confidence by practic-ing and using the prosthesis. Use it or lose it!

Figure5-2: LEFT: The endolite Aqualimb with anto-slip tread patterm on the sole for extra grip on wet surfaces. [www.endolite.com]. RIGHT: The rampro activankle swim-ming prosthesis [www.rampro.net].

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ambUlaTion dUring everday liFe

A very important factor in functional out-come and use of the prosthesis is the amount of energy it takes to use it.

People with amputations tend to walk slower, to bring the power needed to walk to normal levels. Since the disabled person, like the normal subject, tends to choose his most effi-cient speed of ambulation, it seems appro-priate to let the subject pick his own speed, instead of imposing an unnatural speed of walking for the researcher’s convenience. [Seymour 2002, p.166]. Some general proper-ties of ambulation with a prosthesis can be drawn from the averaging of the results of studies in which the subjects did choose their own speed. However, the results given should be taken as approximations and generaliza-tions: [Fisher 1978]

1. The normal person walks 83 m/min and expends 0.063 kcal/min/kg and 0.000764 kcal/m/kg.

2. The average transtibial amputee walks 43% slower, and expends five% less kcal/min and 89% more kcal/m than the normal person.

3. Normal and disabled persons naturally attempt to walk at a speed which is most effi-cient in terms of Ee /kcal/min.

4. Disabled persons decrease their speed of walking, so that their Ee /kcal/min decreases toward the normal range.

5. The more disabled a person, the more deter-minants of gait are lost; therefore, the more Ee /unit distance is used in ambulating and the less efficient is the gait.

Many prosthetist use the thumb rule that using a unilateral transtibial prosthesis takes about 50% more energy than normal. Especially for elderly, this can be very signifi-cant.

Another difficulty can be a limited range of motion in the joints. This can prevent the amputee from climbing and descending stairs, sidewalks, etc. Also, it can slow down the amputee when turning.

sTanding and siTTingRequirement: The prosthesis must enable the patient to stand up fully (else it takes a lot of energy to stand) and to sit (allow enough movement and avoid painful brims).

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5.5 sTaTisTics on FUncTional oUTcome and Use

Practically, how often and intensive the pros-thesis is used, is dependent on a lot of factors, most important being age.

elderly

Functional outcome of elderly is partly pre-dictable by age at amputation, one-leg balance on the unaffected limb and cognitive impair-ment [Schoppen, 2001]. One study found that of 50+ US amputates only 44% wore their prostheses every day [Seymour 2002, p71]. A Canadian study [Bilodeau et al, 2000] shows different statistics: over 70% of amputees 60 years or older used their prosthesis every day. It concludes: “A multiple regression analysis showed that satisfaction, not possessing a wheelchair and cognitive integrity explained 46% of the variance in prosthesis use”. It is safe to conclude that the comfort level of the prosthesis and its easy of use is a major factor determining functional outcome.

yoUng

Younger people are much more forgiv-ing to the design. A study of 88 children of transtibial amputation in the Netherlands found high use rates. 90% of them attended a regular school. This increased use is a result of various factors. These include early fitting, decrease in pain and home and work modifi-cations. [Seymour 2002]

Project:Comfort of fit and use are the most important criteria of the prosthesis

5.6 aFTercare and concerns

Amputation results in social losses due to amputation involve loss of function, loss of sensation and loss of body image [Seymour 2002, p63]. Successful adaptation to the disa-bility results in change of behaviour, such as:

- Increased confidence- Taken charge of life rather than allowing

external factors to control one’s life.- Return to work or hobbies,- Focus on new activities and skills- Renewal of friendships- Increased feelings of independence

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The patient himself is responsible for finding the right support in his neighbourhood, but the rehabilitation team will help him on his way. However, life after an amputation is chal-lenging. The amount of concerns of patients show this [Seymour 2002, p70]:

- Health-care access and expense- Financial concerns- Coordination of social services benefits- Disability rights and advocacy- Lack of knowledge of new prosthetic compo-

nents- Fit of the prosthetic socket- Functioning of the prosthesis- Adaptation to life with the prosthesis- Lack of available information on new tech-

nologies- Accessibility to Commercial Services

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6 ethics,marketinganddesignvision

6.1 eThics

To determine the design target, apart from function and practical requirements, a dis-cussion of ethical implications is needed. It provides insight in the social requirements of the product.

The Universal Prosthesis is a healthcare product. Its benefits for the user are clear. It is evident that there are also benefits for the society. How to optimize these bene-fits? By assessing the positive and negative impact of the product and building on the strengths. The following sections discuss these strengths, especially in the Universal Prosthesis’s final form, as a worldwide avail-able product.

6.1.1 a world-wide smarT-Tech ProdUcT

The Universal Prosthesis is a product that improves the live of the limbless that it is provided to. It is clear that a wide distribution of prostheses is wanted. In developed coun-tries, the amputees are generally provided good healthcare. The wealth is available to improve these person’s welfare and Quality of Life. However, in developing countries, there is still a high unattended need for healthcare. A low-cost universal prosthesis can reach a

big group of customers.

However, low-cost products generally are quite stigmatizing. Even people in need want the best. High-end “Western” products are better accepted. The universal prosthesis could acquire a good reputation by beginning as a high-end product for developed areas. Later, it can become cheaper and available everywhere. In the controlled environment of orthopaedic clinics, the design can be per-fected and later translated to a design that is better suitable for the “stand alone” distribu-tion in developing areas.

How can this evolution from high to low-cost product already be incorporated into the design now? The key is the use of smart-tech and developing a smart-product. A smart product is a product, which development is dependent on high input levels of knowledge. Often, also high-end production facilities and technologies are needed. However, the need for resources and parts in the final product is low. Smart products generally consist of high-end materials. While being expensive at the start-up, the price of a smart product reduces when the investments are turned over, the product can be produced in higher volumes (mass-production) and the price of the used materials and technologies drop as well.

Futurerequirements: The Universal prosthe-sis should consist of few parts. The price of the product (in higher production volumes) should fall in time. The Universal prosthesis should have a high-tech or modern look.

6.1.2 social-PoliTical conseqUences

An important factor to predict the social-political consequences of a product is to look to the influence of the production and use of the product to the distribution of wealth in the society. Will the product contribute to an egalitarian or an in-egalitarian society?

The Universal Prosthesis is a product that helps the users to better fulfil their daily tasks, needs and functioning. This makes them more interdependent of their envi-ronment. There social integration is eased, improving their social, educational and voca-tional chances.

The differences between the transtibial amputees and other people become smaller, also there economical differences. We can say that a prosthesis is a product that advo-cates an egalitatian society by its function.

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Politically, there is a need for high knowl-edge and production technologies to produce the prosthesis. High investments are needed at the start-up of the implementation process. The resources for these investments need to be collected by a small group of people, who gain power by their possibilities. To accommo-date such power/money concentrations, an in-egalitarian society is needed. The differences between the rich and the poor become bigger. However, the improvement in social function-ing of the owners of a Universal Prosthesis has a more powerful egalitarian impact on society. Especially, when the investments are returned and the prosthesis becomes avail-able to the masses for a low price.

We can conclude that on the long run, the Universal Prosthesis will advocate an egalitar-ian society. General healthcare will improve. The effect of the product will be most notice-able in developing countries.

The second limiting factor is economics. There must be enough interest to produce and distribute the Universal Prosthesis worldwide. Even while in this cases humanitarian NGO’s and funds, and social insurance play an enor-mous role, costs will always be an issue.

Demand for the Universal Prosthesis is highly dependent on its comfort level during use.

To combine price, adjustability (to reach new markets) and a high comfort level in one product, a lot of knowledge is needed. Again, the smart-tech approach seems to be appro-priate.

6.1.3 a ProdUcT For The world

In the long term, the Universal Prosthesis will become available to a wide public. It is favourable to integrate this development in the current design.

As seen in chapter two, the distribution and use of the Universal Prosthesis is the limiting factor in the feasibility. Economics comes in the second place.

Important for its distribution is the easy of use. The product must be understandable for a wide range of people, from different cul-tures and languages.

Requirements: use-cues should be multi-lan-guage

Another distribution factor is the (in)dependency of the product on the local infrastructure of resources. For example, it can be assumed that water and electricity are available everywhere but helium-gas is not. The same story goes for dependency on the local infrastructure of knowledge. For exam-ple, electrical-engineers are not available eve-rywhere.

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6.1.4 ProdUcTion

To ensure better distribution the Universal Prosthesis is adjustable. But more is needed.

While designed as a total concept, the Universal Prosthesis will still have a modu-lar setup. Especially the foot, because of the need for different sizes, left-and-right models and varying requirements will have to be produced separately. It could be possible to use existing designs for the feet (produced by now operating companies), but the feet could also be locally produced, in accordance with the local culture and needs.

On the other hand, the socket needs high input of skills and knowledge. It is better to produce it centrally.

A good option to combine these different production places is to offer the product as an assembly kit. The socket is build centrally and imported. Locally, (in the country of distribution) feet and other component are added to complete the kit. Final assembly can be done by the user or the local specialist. This strategy is very similar to current dis-tribution strategies, where components and assembly kits are sold to the prosthetists.

It is well possible (and probably smart) too include many locally made parts in the kit, such as manuals or components. That gives the local production facility the possibility to give the product a local character. People and the local society will feel more involved with the product.

In the world of tomorrow, environmental considerations can’t be ignored. In the case of smart products, when the applied produc-tion methods are reasonable, the product can have a low impact on the environment. Smart products are produced in mass and often effi-ciency of resources is needed. Also, they exist of fewer parts.

6.2 conclUsions From The sri lankan TesT designs

Apart from identifying the lack of prosthetists as the mean problem in devel-oping countries, additional lessons where learned from the design made there and the tests conducted.

Trials of amputees walking in open-frame sockets (see appendix D for some designs) indicate that open-frame sockets can be used to stand in. During ambulation the test-models in Sri Lanka buckled within a few steps.

Figure6-1: A movie, in which an amputee walks several steps in a frame socket. [Wisse et al. 2002]

WATCHTHEVIDEOONTHECD

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6.3 markeTing In chapter four we have seen that current prosthetic design vary widely in quality (com-fort level) and price. The market in developing countries is completely different than that in western markets. This results in different cri-teria, a different maximum price and a differ-ent value the users will give to the universal prosthesis.

Because the current state of prosthetics in developing countries has to be improved (and the amputees won’t accept else!), compromis-ing comfort is not an option.

Given the high requirements on comfort level, it is challenging to offer the universal prosthesis for a low price (for a better fit, more or better adjustable parts are needed). This leads to a multi-step approach to the world market. Because each step requires a new design (optimization), the phases in this approach are referred to as cycles:

This is an important find. If an open-frame socket can be used to stand in during the fit-ting procedure, the prosthesis can be fitted while the residual limb is under load. A total contact socket can than be formed in respect to the loaded limb. The resulting unique fit-ting procedure will result in:

- higher pressures on the interface between the limb and the open-frame on pressure-tolerant area’s (see section 3.1.3)

- less tissue deformation during load (prosthe-sis will be formed to the situation when the highest pressures find place). This results in more comfort during stance and probably to a higher overall comfort.

These intermediate finds strongly suggest that the universal prosthesis should exist of a hard open-frame part and an easily deform-able soft part.

These results indicate that open-frame sock-ets can be used to stand in and might be developed further, so that even ambulation is possible.

The open-frame design was never reported as being comfortable. One problem was the connection between the back and front part of the open-frame (usually a leather belt). The system had to be very precisely dimensioned and stiff connected; otherwise the amputee would slip downwards into the prosthesis (pistoning).

To achieve a comfortable fit (a level of com-fort comparable to current sockets) as many areas as possible must assist in weight-bear-ing and control (up to their maximum pres-sure tolerance).

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- Cycles2:-Standardgroup”, “Kids” and “Inactive”. The final design has to combine all the positive sides of the universal prosthesis. If feasible, multiple versions will improve the comfort for the target groups. The “UP Kids” can be smaller and the “UP Senior” can be lighter than the “UP Standard edition”.

- Cycle0-Thepreparatorydesigntrajectory:In this phase, the feasibility of the universal prosthesis is shown by developing a proof-of-principle design (this graduation project) and testing it with users (continuation).

- Cycle1-Marketexploitationindevelopedcountries:A high quality (medium-high costs) design is made. In this phase, the design is tested on a broader scale, while production quantities can stay low. It will be used by many experienced prosthetists, whose feedback is invaluable.

- Cycle2–Worldmarketexploitation:A high quality, low coast design is made. The product can be low in costs because the product is produced in large quantities (>10,000 a year). This high volume production is supported by a well organized distribution around the world (compare 6.1.4).

Each cycle will have a different target group. Most users of the universal prosthesis will be part of these groups:

- Cycle0–“Standardgroup”: Healthy man and women with a unilateral transtibial amputation. The age group for which the universal prosthesis is designed, will be around 20-60, because (anatomical and statistical) data is used from this age-group (see appendix G).

- Cycle1–“Inactiveamputees”: such as bed-bound people, because the lim-ited use of the prosthesis leads to low struc-tural/mechanical demands. In this case, the universal prosthesis can be designed lighter (and more easily adjustable if deformation forces are needed). The quickly fitted prosthe-sis results in more elders that are fitted.

- Cycle1–“Kids”: The lower body weights leads to low struc-tural/mechanical demands. Also, because of the growth of the younger, more frequently new prostheses have to be fitted. The univer-sal prosthesis can lead to a higher replace-ment rate. The design can be smaller, or issued in multiple sizes.

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Water-cast: wrap residual limb in plaster of Paris, put limb in pressure-tank, add pressure while hardening, make a positive with plaster of Paris, laminate with fibre and resin.

Icex:Fit liner with silicone pads to protect bones, prepare Icecast component, calibrate, wrap limb, shove on residual limb, harden (plaster of Paris or directly laminated), finish.

Universalprosthesis:For an impression see sec-tion 6.5.

A scan of the advantages of the systems can be found in table 6-1. Concluding from it, if the universal prosthesis can keep its promise, it will be a good alternative (also see evalua-tion chapters).

to alleviate the same problem as the universal prosthesis does, namely, the lack of experts and the difficulty of making new prosthetic (sockets). They compare as follows:

basic ProcedUres:Standard: make a negative of the residual limb

with plaster of Paris, make a positive with plaster of Paris, rectify for pressure distribu-tion, laminate with fibre and resin.

Sand-cast: put residual limb in plastic bag, Put the limb in a container, fill the container with sand, suck air out of container (negative shape forms), fill the negative with sand and evacu-ate air (positive sand form), rectify, vacuum form or laminate socket.

6.4 sUbsTiTUTe ProdUcTs and comPeTiTive FiTTing meThods

Most direct competitive products for the universal prosthesis are mentioned in chap-ter 4, during the discussion of the different prosthetic types. However, the most distinc-tive property, the fabrication method, is only discussed very briefly in section 4.1.5.

For the acceptance in developing countries, the prosthesis has to be more wanted than two important substitute products, the wheel-chair and the cane.

6.4.1 FabricaTion and FiTTing meThods

In section 4.1.5 the standard fabrication method is shown (figure 4-9) and the ICEX-system is introduced, which is an example of a pressure-cast method (see 4.3.1). Its fabrica-tion manual can be found in appendix N. The sand-cast-method is developed for use in the third world as another pressure-cast method (fabrication details in appendix O). Finally, the water-cast-method, currently in develop-ment at orthopaedic centre “de Hoogstraat” in Utrecht and the University of Strathclyde, is developed with the same target group in mind. These last three, all pressure casts, aim

Product Rectification? Expertiselevelneeded?

Toolsneeded

Standard Yes (PTB) High often vacuum formingSand-cast Yes (PTB) Medium-High Pressure device + air-tight containerWater-cast No Low Pressure device + water-tight fitting-tankIcex No (but pads) Medium-High Icecast compact componentUni. Pros Yes (PTB) Low None other than for do-it-yourself (saw,

screwdriver, etc)

Table6-1: Several fitting methods and their properties.

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Product Comfort Availability/support PriceProsthesis The prosthesis can be very comfortable, but the user has to

have a decent residual limb (health and length). Social accepta-tion is high.

A comfortable prosthesis is difficult to make. Because of this, properly functioning prostheses are not wide-spread. On the other hand, a robust prosthesis can be used in many situations (city, farmland, etc)

± 100

USD

Wheelchair The comfort level of the wheelchair is high, especially for people with difficult amputation levels.

Wheelchairs are easy to manufacture from blue-prints. Wheelchairs are wide-spread, but use is limited because the user needs flat roads and other adaptations of the environ-ment. These adaptations are part of normal life in developed countries, but not so in developing countries.

± 100 USD

Cane The comfort level is low during ambulation. The user needs an arm while walking. However, the cane can easily be put away. Social acceptance is low, but some make use of this (beggars).

With a cane most places are accessible. Also, canes are easily produced and distributed

± 10 USD

UniversalProsthesis

High-comfort fit made possible without expertise for a select group (of medium-active, healthy, transtibial amputees).

Better distribution ? USD

Table6-2: Several walking and mobility aids and their properties

6.4.2 sUbsTiTUTe ProdUcTs

The wheelchair and the cane are widely spread and used in developing countries. They compare as presented in table 6-2.

The universal prosthesis can alleviate the problem with the quality of currently pro-duced prosthetics in developing countries. It will stay more expensive than a cane, and 100 USD will stay a high amount for a large part of the world population. The wheelchair has to be available, especially for people with other amputations or disorders than a transtibial amputation.

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easily visible from the outside of the pack-age. On the box is basic information about the range in stump shape, circumference and length for which the kit is suitable.

disTribUTion:- The kits cost about 500 USD.- The kits are being advertised as an

(cost)effective, customizable, base from which a prosthetist can (time)efficiently fit a prosthe-sis.

- The kits are being sold via existing reselling companies, from two centralized points, one in the United States and one in Europe.

- The kit is bought in conjuncture with a serv-ice contract. This service contract will help the prosthetists with information and will sell additional parts when needed. The service contract will provide the producer of the uni-versal prosthesis with addition feedback on usage and functioning.

Use – FiT and alignmenT ProcedUre:- The kits are easy to lift, they don’t weigh more

that 5 kilograms. The can be easily stored due to their form.

- The prosthetist opens the kit, when basic information on the residual limb is known, before the patient arrives, so he has time to prepare the parts he will need. The socket can be connected to a fitting pylon/foot if the prosthetist doesn’t know yet which type of foot he will use for his client. If he knows, he can immediately connect the selected foot.

6.5.1 cycle 1 – For develoPed coUnTries

design and ProdUcTion- After the feasibility of the concept is proven,

the product has to be developed into a final design. This development can be conducted at universities or at one of the big compa-nies, such as Otto-Bock or Ossur, that can finance it. A new team, combining industrial design engineers, technical engineers and prosthetists optimizes the design. The exist-ing requirements list (chapter 7) defines the design target.

- With a small number prostheses clinical tests are conducted to answer questions as:

“can the universal prosthesis find its way in current (orthopaedic) practise?” and “what is long-term functional outcome?”.

- Now, after evaluation and redesign, produc-tion can be started. The first batch will exist of 10,000 pieces. The assembly of the pros-thetic parts is mostly left to the prosthetists. They buy assembly kits, so that they have greater influence on the final shape of the fitted prosthesis. The kits don’t contain feet, which are easily available through the common distribution channels.

- The kit contains: a manual for the prosthetist, a manual for the user, the parts needed for the prosthesis, additional parts that can improve the fit for non-standard residual limbs (such as gel pads), a brochure that explains the long term project objective. The main part of the prosthesis, the socket, is

6.5 vision oF The FiTTing ProcedUre and Usage

The results in Sri Lanka (section 6.2), com-bined with the market possibilities from sec-tion 6.3 and the project and vision remarks found all over chapter 3 and 4, lead to one vision about how the prosthesis and its fitting procedure should be. This vision is hereafter presented for both cycle 1 and 2 and follows the life-cycle of the product (design and pro-duction, distribution, fitting procedure, use by patient, disposition).

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Use- daily Use by The clienT:- PREPERATIONS: The socket has to be clean,

especially on the inside. The user can, depend-ent on the type of foot that was provided with the prosthesis, don socks and shoes over the prosthesis.

- DONNING:The user dons a liner or sock. The prosthesis is donned over the liner or sock. If needed, a suspension belt or sleeve is attached.

- AMBULATION:The client now can do his normal, daily activities. In the beginning, the patient has to get used to the prosthesis. He has to gradually increase the daily period of use.

- DONNING: The prosthesis is donned. It can be stored everywhere. Socks need to be washed.

- MAINTENANCE: For reparations and main-tenance, the client visits the prosthetist. The prosthesis is checked every half a year.

disPosiTion- The prosthesis is returned to the prosthetist,

who will provide a new one. - The prosthetist detaches the foot. - The prosthetist sends the prosthesis back to

the factory. The factory will check the pros-thesis on wear and will evaluate the way it was used.

- When the patient arrives, the basic setup is ready. The patient has to sit and to stand during the fitting procedure, so a frame or a walking aid and a chair are needed. The order of the parts in the box support the procedure the prosthetist has to follow.

- SITTING:To protect the residual limb of the client, a sock is donned. The still (de)formable socket is being donned over it. The prosthetist adjusts the total limb length by adjusting the length of the pylon. The socket is provided in its biggest shape, the prosthetist can by deforming it, globally adjust the form to the shape of the residual limb. If needed, gel pads or gel stickers are attached on the sock over wounds or extra-sensitive areas.

- STANDING:The patient can stand now. The hard part of the socket provides weight bear-ing. The pylon is aligned in such a way, that the line of gravity is normal on the axis of rotation of the knee. The feet of the patient have a natural distance and angle.

- STANDING:The soft part of the socket now exactly forms itself around the loaded residual limb. The prosthetist can aid this formation. When the soft part has the right shape, the prosthetist starts the hardening phase. The soft socket now quickly settles, the complete hardening doesn’t take longer than 10 min-utes. Meanwhile, the patient is standing in the prosthesis (with about half its body weight supported by the prosthesis).

- SITTING:The prosthesis now can be doffed. The fitting sock and gel stickers can be dis-posed of. A thin liner or sock (as thick as the fitting sock) can be worn during the use of the prosthesis.

- AMBULATION:The client walks. The pros-thesis now behaves as a PTB-prosthesis. To improve pressure distribution (more TCB-behaviour), a thick, but viscous liner is donned. The user himself can choose the most comfortable combination.

- The fitting procedure is finished. The fitted pylon and foot are definitely attached to the socket. The client can take the result home, together with the manual. Not-used parts, which might be used later for repairs or when a new prosthesis is fitted, can be given to the client or send back to the factory.

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- SITTING: To protect the residual limb of the client, a sock is donned. The still (de)formable socket is being donned over it. The helper adjusts the total limb length by adjusting the length of the pylon. The length can be easily determined by comparing the resulting knee heights. The socket is provided in its big-gest shape, the helper can, by deforming it, globally adjust the form to the shape of the residual limb. If needed, gel pads or gel stick-ers are attached on the sock over wounds or extra-sensitive areas.

- STANDING: The patient can stand now. The hard part of the socket provides weight bear-ing. The pylon is aligned in such a way, that the line of gravity is normal on the axis of rotation of the knee. The feet of the patient have a natural distance and angle.

- STANDING:The soft part of the socket now exactly forms itself around the loaded residual limb. The helper can aid this forma-tion. When the soft part has the right shape, the helper starts the hardening phase. The soft socket now quickly settles, the complete hardening doesn’t take longer than 10 min-utes. Meanwhile, the user is standing in the prosthesis (with about half its body weight supported by the prosthesis).

and a liner. The final product (after fitting pro-cedure) is shown on the outside of the box. On the box is shown for which residual limb sizes the prosthesis is suitable and the size and side of the foot that is in the box.

disTribUTion:- The kits cost about 100 USD.- The kits are being advertised as a good, com-

plete and easily fitted prosthesis..- The kits are being sold in every country from

centralized spots. - Additional parts are easily available through

the centralized selling points.

Use – FiT and alignmenT ProcedUre:- The kits are easy to lift; they don’t weigh more

that 5 kilograms. The can be easily stored due to their form.

- The user is able to fit the prosthesis himself, but aid is useful. The helper and the user together open the kit.

- The order of the parts in the box supports the procedure the users have to follow. The socket, the pylon and the foot are connected by them. The user has to sit and to stand during the fitting procedure, so a frame or a table and a chair are needed. For the functioning of the prosthesis, a right alignment of the feet is required. The user can easily see this on the fit-sheet, which is placed on the ground and has an image of to feet printed on it.

6.5.2 cycle 2 – For develoPing coUnTries

If the use of the prosthesis is successful in the developed countries, the transition to the use for the developing countries can be made.

design and ProdUcTion- After the success on the markets in the

developed countries, the product has to be improved further. The producers of the prosthesis, in combination with subsidy and grants, finance the new development. The new team, again with multi-disciplinary now also combines members from all around the world.

- With a small amount of prototypes new clini-cal tests are conducted. Now, the ability of the prosthesis to function in area’s such as farmland and the ease of fitting need to be assessed.

- After redesign and optimization, mass produc-tion can be started. At least 10,000 pros-theses a year are fabricated. The prosthesis will be as much as possible pre-assembled in the factory. The result will be distributed in assembly kits, which consist of the socket parts, pylon and a foot.

- The kit contains: the parts needed for fabri-cation, a manual for the one who will help during the fitting procedure (hereafter called helper), a manual for the user, a fit-sheet with feet positions printed on it and gel-stickers

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disPosiTion- The prosthesis can be send or brought back to

the factory, who will issue a new kit against a slightly reduced price.

- SITTING:The prosthesis now can be doffed. The fitting sock and gel stickers can be dis-posed of. A thin liner or sock (as thick as the fitting sock) can be worn during the use of the prosthesis.

- AMBULATION: The amputee walks. The prosthesis now behaves as a PTB-prosthe-sis. To improve pressure distribution (more TCB-behaviour), a thick, but viscous liner is donned. The user himself can choose the most comfortable combination.

- The fitting procedure is finished. The user take the result home, together with the manual and unused parts, which might be used later for small repairs.

Use - daily Use by The clienT:- PREPERATIONS:The socket has to be clean,

especially on the inside. The user can, depend-ent on the type of foot that was provided with the prosthesis, don socks and shoes over the prosthesis.

- DONNING:The user dons a liner or sock. The prosthesis is donned over the liner or sock. If needed, a suspension belt or sleeve is attached.

- AMBULATION: The client now can do his normal, daily activities. In the beginning, the patient has to get used to the prosthesis. He has to gradually increase the daily period of use.

- DONNING:The prosthesis is donned. It can be stored everywhere. Socks need to be washed.

- MAINTENANCE: Small reparations and adjustments can be done by the user himself. For bigger defects, a new prosthesis has to be fitted. The manual will advice the user to replace the prosthesis every year.

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7 designcriteriaandrequirements

In chapter 3 it became clear that transtibial amputation is the most prevalent level of amputation. Therefore, the universal prosthe-ses should be usable by this group. But what are other requirements? Ten criteria, which are constantly used while evaluating ideas, and the total concept can be found in section 7.1.

The requirements (Dutch: eisen) are depend-ent on the cycle (see section 6.3) in which the development of the prosthesis is. However, requirements for a later cycle, are always goals (Dutch: wensen) for the preceding cycle. That’s why the requirements can be found per cycle (section 7.2 to 7.4). Additional goals can be found in section 7.5.

A good list of requirements only consists of requirements for the design and doesn’t con-tain solution on how to meet these require-ments. In the list of requirements hereafter, this principle is not used. This project is a continuation from the internship in Sri Lanka and the results of that work determine the global design and project form.

1. UniversalThe prosthesis can be fitted to a big group of transtibial amputees.

2. ComfortableThe prosthesis is comfortable during use by the amputee.

3. Easilyfitted The prosthesis can be fitted easily to the amputee by low educated.

4. Controllable The prosthesis provides the control and feed-back during use.

5. Usable The prosthesis can be easily used (espe-cially donning, doffing and cleaning) by the amputee.

6. Safe The prosthesis is safe in respect to health of the user and of the planet.

7 Affordable The price of the prosthesis is low.

8 Cosmetics The cosmetics of the prosthesis are pleasing. The amputee blends easily into the society.

9 Quicklyfitted The fitting procedure takes little time.

10 DistributableThe distribution is easy and the prosthesis is complete or well compatible with other systems. The (fitting of the) prosthesis is inde-pendent on locale infrastructure.

The list of requirements also isn’t complete. The complete set of requirements relates to the complete service that de producer and the prosthetist offer to the client (of which the prosthesis is a part). That would be a long list. Here is chosen for a shorter, better usable list, that suits the purpose of this project, namely to conduct a feasibility study. Areas which won’t be the bottleneck for the feasibility of the project are not worked out.

7.1 Ten design criTeria Design criteria follow from what the design needs to be successful. The design can comply with the criteria in a higher or lower level (score better or worse). In order of importance the 10 criteria are:

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7.2 reqUiremenTs For cycle 0: The PreParaTory design TrajecTory

Corresponding sections are given between brackets ().

ToTal disTribUTion kiT /ProsThesis:- The prosthesis can be donned seated.- The prosthesis can be doffed seated.- The prosthesis has roughly the same shape as

the natural leg.- The fitting procedure takes little time.- The prosthesis is suitable for at least 70% of

the transtibial amputees (2.3).- The prosthesis improves the functional activi-

ties and mobility of the user in a similar way as existing prostheses. Inclusive ambulation and body posture.

- The prosthesis provides an acceptable gait (3.1.5).

- Ambulation is possible without the toes touching or skimming the ground.

- The prosthesis provides enough stability (during ambulation that resembles normal gait).

- The prosthesis provides enough perception and control.

The sockeT:- The interface with the residual limb can not

be poisonous or irritate the skin (for P99).- The socket is suitable for more than 70% of

the transtibial amputees (2.3). - The socket is suitable for residual limbs with

lengths of 80 to 250 mm (3.1.2, 3.1.3). - The socket is suitable for residual limbs with

circumferences of 250 to 350 mm (at patellar tendon height) (3.1.3).

- The socket is suitable for residual limb shapes that are conical and cylindrical (3.1.3)

- During the fitting procedure: - The socket is formed while the residual

limb is loaded (while the user stands in it): - The socket provides weight-bearing at

beginning of the procedure. The unhardened socket is enough flexible and deformable, so that the prosthetist can shape it in the shape of the residual limb.

- The socket loads the pressure-tolerant areas of the residual limb.

- The socket has to harden so that the total area can add up to the transfer of loads between the socket and the residual limb. The prosthetist has to be able to decide the moment of the hardening. The hardening won’t take longer than ten minutes.

- During daily use: - The sensitive areas of the residual limb

will not be overloaded. Most of the loading is on the load tolerant areas (3.1.3 – 3.1.5).

- The socket makes total contact with the residual limb. Every area of the residual limb, inclusive the distal end, has to make contact with the socket (so no “holes”) (4.3.1)

- The pressure-distribution is optimized to the PTB or the TCB-model or a hybrid/combi-nation of those. (4.3.1)

- The socket is not uncomfortable (2.3), the comfort level is comparable with existing prostheses. (4.3.1)

- The socket does not hurt. - The socket does not obstruct normal

movement. - The socket can not have obtruding or

sharp parts as well on the inside as on the outside.

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7.3 criTeria For cycle 1: markeT exPloiTaTion in develoPed coUnTries

Corresponding sections are given between brack-ets ().

ToTal disTribUTion kiT /ProsThesis:- The product is optimized for production quan-

tities over 10,000 pieces. (4.1)- The prosthesis complies with the current

West-European and American industry stand-ards. (3.3)

- The final price of the distribution kit is maxi-mal 700 USD. Using the universal prosthesis will (in general) reduce the costs of the total rehabilitation trajectory. (4.5.1-4.5.5)

- The prosthetist assembles the socket, the pylon and the foot within 2 minutes, so that it is ready to be fitted.

- The final prosthesis will weight between 2.2 and 3.5 kilograms (3.1.4, 3.1.5) with the centre of gravity of the prostheses as proxi-mal as possible.

- The prosthesis will stay functioning properly at normal use (average usage of the target group) al least one year. (4.6)

- The prosthesis doesn’t attract attention when worn under a pair of trousers, socks and shoes (4.1).

- The donning and doffing of the prosthesis does not take longer than one minute (5.4).

FooT:- A “rocker foot” suffices.

addiTional ParTs:- SUSPENSION: The comfort level has to be

minimally equal to the comfort level of the currently used “knee-cuff” solution.

- CONNECTIVE COMPONENTS: The connec-tion between the socket and the pylon can be rotated. The connection between the pylon and the socket can be rotated.

Pylon:- The pylon can be adjusted in length. The total

height of the prosthesis is the same as that of the opposing leg.

- The pylon can transfer the forces that act upon it during stance (maximal 700 N) to the ground without plastic deformation. The total elastic bending may not be more than 6 mm at a length of 240 mm and the total elastic rotation may not be more than 10 degrees, when the pylon is loaded with a torque of 60 Nm at a length of 240 mm.

- The pylon can be aligned: - The pylon can be aligned is such a way,

that the medial side transfers more load than the fibular head region (3.1.4).

- The alignment is done with 5 to 10 degrees flexed knees (3.1.4).

- The complete prosthesis can be aligned in such a way, that the rotation-forces on the residual limb while standing are minimal (no more than current prostheses) (4.4).

- The pylon can be aligned in such a way that the line of gravity of the body will be normal to the rotational axis of the knee during stance.

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Packaging and manUals:- The manual for the prosthetist contains a (tex-

tual) description of the preferred procedures. - The manual for the user contains information

about donning and doffing, the maintenance and cleaning of the prosthesis, how the user can recognize problems and what actions to take.

- OPTIONAL FOR CYCLE 1: A brochure that explains the long term project objective.

- On the outside of the distribution box (pack-aging) is printed for what range of residual limb sizes and shapes the prostheses is suit-able. The socket is visible from the outside of the packaging.

- The total package is easily displaceable by a single person. It is not bigger than 0,12 M3) and it has sides shorter than 800 mm. The package is not heavier than 5 kg.

- The order in which the parts come out of the package supports the fitting procedure.

- The prosthesis aids the prosthetist in finding the right alignment (use-cues). The prosthetist has to experience the fitting and alignment procedure as more natural and intuitive than the procedures of current prostheses (2.3-4.4).

- The prosthesis is suitable for daily use (2.3).- The energy expenditure of normal use of the

prosthesis is comparable with that of current prostheses (maximal 30% more) (3.1.5).

The sockeT:- The total production cost of the socket is

maximal 500 USD.- The socket must be easy to clean (5.4).

Pylon:- The total production cost of the pylon is maxi-

mal 100 USD.- The pylon can be fitted with a shock-absorp-

tion component or rotator.

FooT:- REMARK: In this distribution kit, no foot is

supplied. Standard feet designs can be con-nected to the universal prosthesis.

addiTional ParTs:- SUSPENSION: The included suspension will

keep the prosthesis connected to the residual limb during swing-phase.

- CONNECTIVE COMPONENTS: The included connective components provide connection with popular feet designs. The connection to the feet stays adjustable (translation and rota-tion), even when the prosthesis is hardened. (4.2)

- FITTING SOCK: The supplied fitting sock can be donned sitting. The fitting sock protects (the skin of) the residual limb during the fit-ting procedure.

- PRESSURE-RELIEVING-PARTS (GEL PADS): These included parts will diminish the pres-sure on extra sensitive areas of maximal 600 mm2.

- FITTING PYLON – OPTIONAL FOR CYCLE 1: The fitting pylon is an extra pylon part that can be attached to make up for the lacking foot during the fitting procedure.

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FooT:- The total production cost of the foot is maxi-

mal 30 USD.- The foot has a natural appearance. - The foot is available in left and right. - The foot is available in several sizes.- The foot can be fitted with sandals.

addiTional ParTs:- CONNECTIVE COMPONENTS: The included

connective components provide connection to the included foot. The connection to the foot stays adjustable (translation and rotation), even when the prosthesis is hardened.

- FITTING SOCK: Included.- SOCKS FOR DAILY USE: Included in 2 thick-

nesses. The wearing of these socks increases the pressure in the socket.

- LINER FOR DAILY USE: Included. Wearing of the liner results in a more evenly distributed pressure in the socket.

- PRESSURE-RELIEVING-PARTS (GEL PADS): Included.

- FEET-SHEET AND OTHER ASSISTIVE DEVICES: Simple products that can improve the ease of aligning (the residual limb in) the prosthesis.

7.4 criTeria For cycle 2: world markeT exPloiTaTion

Corresponding sections are given between brack-ets ().

ToTal disTribUTion kiT /ProsThesis:- The final selling price of the distribution kit is

maximal 200 USD.- The total prosthesis will keep functioning sat-

isfactory for two years when normally used.- The assembly has to be finished as far as pos-

sible in the factory. Pylon and socket are one part.

- The prosthesis can be worn without shoes (without attracting negative attention).

- The prosthesis can be fitted by non-experts.

The sockeT:- The total production cost of the socket is

maximal 80 USD.

Pylon:- The total production cost of the pylon is maxi-

mal 30 USD.

markeTing:- The distribution kit is being advertised as an

(cost)efficient, customizable, base from which a prosthetist can (time)efficiently fit a prosthe-sis.

- The kit is bought in together with a service contract.

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FooT:- The included foot is suitable for multiple

weights, multiple foot sizes and for left and right use (adjustable foot).

addiTional ParTs:- SOCK: The sock is transparent. The sock is as

thin as possible. The fitting sock and the sock for daily use are the same.

- SUSPENSION: The suspension is as easy and comfortable as current suction suspensions.

markeTing:- In an early stage, a big organization (pro-

ducer), such as Otto-Bock or Ossur is involved.

Packaging and manUals:- The manuals are internationally interchange-

able. It uses mainly figures / drawings. - On the package (distribution kit) the final

product and the included foot-size and foot-side are printed.

markeTing- The kits are being advertised as a good, com-

plete and easily fitted prosthesis.

7.5 addiTional goalsIf possible, the following goals can add value to

the solution:

ToTal ProsThesis:- The prosthesis is adjustable after the fitting

procedure.- The prosthesis is as light as possible.- The prosthesis fits into the locale culture.

(Part of the) production is conducted locally. Local, social involvement is stimulated

- The prosthesis exists of as few as possible parts (2.3).

- The prosthesis is accepted by the total reha-bilitation team (3.2)

sockeT:- The socket is transparent (makes evaluation

of the interface between the socket and the residual limb easier)

- The socket is adjustable during use (adjust-ments take place several times a year).

- The socket is adjustable during use (adjust-ments take place multiple times a day).

Pylon:- The pylon is adjustable during use (adjust-

ments take place several times a year)- The pylon is an integral part of the socket and

forms an exoskeletal design (4.2).

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8 discussionandconcLusionoFPart1

The analysis indicates that the design an implementation of the universal prosthesis is possible, although with some constraints.

a broad range oF markeT oPTions.In chapter 2 the benefit for users all around the world, amputees and prosthetists, becomes clear. The fact that designing a prosthesis takes time is recognised and the project is split into phases. These phases are design cycles and are “a preparatory design trajectory”, “market exploitation in developed countries” and “world market exploitation” (see section 6.3).

The unique selling point of the Universal Prosthesis is that it is quickly fitted by low-educated experts. For the amputee, this means better access to prosthetics and more often replaced prostheses. On the other hand, because the shape of the socket has to be formable, the strength and stiffness of the Universal Prosthesis could be limited. These facts combined indicate that the Universal Prosthesis is especially suitable for two spe-cific target groups, namely children and elder (see section 3.1.7 & 6.3). It also is useful as a temporal prosthesis (3-6 months after amputation) or a spare one (see section 2.4, 4.1.4). When, by smart design, stiffness and strength become less a problem, the Universal Prosthesis can be used for daily activities.

a high comForT level can be reached

A high comfort level of the socket can be reached best if pressure tolerant areas are loaded more than pressure intolerant areas (PTB-principle, section 3.1.3). The bony prom-inences (figure 3-6) and the distal end are the areas of relief and the patellar tendon is very pressure tolerant. The limited variation in these areas (except in distal end height) indicated that a standard socket shape is pos-sible (appendix F, elaborated on in chapter 11 and appendix R).

J. Foort (appendix X) even concludes that the use of prefabricated Below-knee sock-ets “taught us that five sizes for each side of the body were sufficient to fit all the new amputees managed in this way and that one size alone met 50% of the needs”. However, the use of prefabricated sockets in current prosthetic practise is not mainstream. The adjustability of the universal prosthesis could improve the trust prosthetists have in the fit of the prefabricated (universal) socket and increase it use.

FocUs on FiTTing ProcedUre

Still unclear in the design objective (see sec-tion 2.4) is if the adjustability of the design refers only to the fitting procedure or also to periodically or even daily adjustments. However, it became clear that comfort and control acre the main determines for func-tional outcome (see section 5.5) and these requirements are met by a socket with a stiff fit and an appropriate pressure distribution (see section 3.1). Current solutions for daily adjustable sockets are few and only improve comfort significantly for a very select group of users. Adjustability of the socket during use therefore is not a requirement for the Universal Prosthesis to be successful.

The pylon has to stay adjustable. To allow for dynamic alignment of the pylon/foot after socket production is an important factor to improve gait and will make the Universal Prosthesis easier accepted by current day prosthetists (see section 3.1.4).

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a vision oF The sockeT design

User tests in Sri Lanka show that weight-bearing in a frame is possible, but total con-tact is necessary for comfort. This leads to a socket system that consists of a hard, weight-bearing frame and a flexible total contact part. The form and properties of these are determined in part 2 of this report: “synthe-sis”.

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9 synthesis-FromideatoProsthesis

Having determined the project target and design requirements, the materialization of the design can begin.

The base for the new design is the design made in Sri Lanka. However, because of changes in the design philosophy (from cheap production to easy fitting procedure) and the preferred production method (from low-budget to mass-production) a review of the (sub)problems is needed (section 10.1) and solutions need to be re-evaluated (sec-tion 10.2). The real synthesis can now take place; the chosen ideas are integrated into a final concept (section 10.3).

In part 3 (chapter 12, 13 and 14) of this report, the universal prosthesis will be evaluated.

The result exits of rigid and flexible parts. The form of the rigid parts needs to be refined. A study of the anatomy of the residual limb and the (expected) biomechanical behaviour is the basis for their shapes (section 11.1). The (fabrication of the) flexible parts is another important design step (section 11.2). The con-nector, connects these parts with the foot (section 11.3). When the shape of the frame is determined, the prosthesis is ready to be optimized for daily use (11.4), the fitting pro-cedure (11.5) and production (11.6).

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10ideas

In Sri Lanka it became clear that weight bearing can be achieved by making an open-frame based socket (see section 6.2). However, made from aluminium and basic production methods, the open frame socket was not comfortable enough to be used for ambula-tion (for a prolonged period of time). Another problem was that the design was not stiff and strong enough, which resulted in buckling (during ambulation).

A better fit and pressure distribution as well as higher stiffness and strength can be achieved by new form-giving and new mate-rial choice.

conFlicTs in The criTeria

Two specific equilibriums need to be found in opposing criteria which are:

Variable vs. stiff Stiffness is an important aspect of safety and control, while variability or adjustability is an important aspect of the universality. How can the prosthesis be made stiff enough, while still being variable? We know that the prosthesis will incorporate an open-frame socket design. Therefore this question can be restated as: (3) “How to make a frame (that can transfer loads) deformable?” and (4) “How to attach a deformable part to a rigid skeletal frame?”.

Comfortvs.control More control can be achieved by a tighter fit, which means higher pressures. However, control is more important during ambula-tion/stance than during sitting or swing, so the problem is: (9) “How can a tight fit be accented during load and a comfortable fit during rest?”.

Another way to improve comfort is to reduce pressure-peaks by vertical dampening. The problem is: (10) “How to improve vertical dampening while keeping control (and direct sensory feedback) during use?

The problems are explored in appendix Q. The presented solutions were obtained by looking at existing solutions, looking into other products with similar problems and by creative thinking.

10.1 idea generaTion

From the criteria and design requirements, sub-problems follow:

1 Universal (1) How can one socket vary in length, circumference or shape (the socket has to be hollow)? (2) How can one pylon/total prosthesis vary in those properties (the pylon can be solid)? (5) How to align a load-able frame or pylon?

2 Comfortable (6) How can one prosthe-sis make total contact with different shaped residual limbs? (7) How to improve weight bearing properties and pressure distribution in the socket?

3 Easily fitted (8) How can the fitting procedure made easier?

4 Controllable (together with 6) How can a tight fit be assured by a wide range of residual limb shapes?

5 Usable (11) How can a prosthesis be donned and doffed? (12) Even when the patient has a bulbous residual limb shape?

6 Safe (13, 14, 15, 16) How can stiffness and strength be guarantied?

7 Affordable (Optimization)8 Social (Optimization)9 Quickly fitted (Optimization)10 Distributed (17) How can integration with

existing parts (connective components and the suspension system) be made easy?

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1The “flower principle” is a very interesting to use for an adjustable socket. It promotes a pylon at the distal end of the socket and the “opening of the flower” is the normal response of shell parts when loaded from the inside (when you try to stand in it. The flower prin-ciple can be used, but the normal response should be counteracted, for example, by a belt all around the socket.

The “multi-link” option is also very interest-ing. Theoretically, the more parts an open-frame socket consists of, the better the fit is that can be achieved. J. Foort formulated the potential usefulness of the multi-link option in 1977 and proposed that “Shapeable matri-ces can be used to construct biomechanical structures directly”.

However, elements of which these shapeable matrices should consist of are not satisfac-tory developed until now. Cousins proposes that “hybrid modular-matrix systems may develop as stepping stones to either matrix or modular structures” [J Foort, 1986]. The Universal Prosthesis, with its hard open-frame and connective soft-frame parts does in a way resemble a modular-matrix system. Belts as seen in the “ellipse with belts” option are suitable to transfer tensile forces between frame parts over a variable length. If adjust-

able belts are chosen as part of the final solu-tion, the user has to be able to determine the length of the belt quite precise. (see 6.2). The “harmonica” option can also be used in a tapered socket shape, so it can accommo-date for variable stump sizes and lengths.

10.2 idea discUssion

Subproblems and ideas (solutions) can than be evaluated by rating them against the 10 criteria. However, selected solutions have to be integrated into one prosthesis. Also, we know that the socket will exist of hard and soft parts and that the hard parts will func-tion as an open-frame socket (see 6.3). It is therefore important to select idea’s that inte-grate well into each other and that contribute to an integrated fitting procedure.

Hereafter follows a short discussion and some considerations of the subproblems and the solutions that can be found in appendix Q.

Each number correspondences with the number and the figures in the Appendix.

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2 The “saw it” option for the pylon is basic and can be integrated well into designs that can only be fitted once (can only be made shorter after the fitting procedure). For addi-tional adjustments during use, a combination with the “telescope” or “screw it” options can be chosen.

3 Building the prosthesis from parts that are deformable of displaceable when separated, but are that are rigid when con-nected, is a good option. It compares well to a modular “Lego” kind of build-up.

”One-way-deformation can be unsafe for the patient and result in a locked-in residual limb. On the other hand, it might be a useful tool during the fitting procedure. In this case, the

“one-way-deformation” has to be reversible or to be reset.

4 “Gluing parts together” is a good option in case it can be done during the pro-duction of the prosthetic components. Glue is difficult to use during the fitting procedure: it can get quite messy and results may vary. These difficulties can partly be removed by using a bag around the glue and the parts that need connecting. However, in this last case it is difficult to add a reaction agent or to start the reaction otherwise.

“wraps” can be used, especially in combina-tion with Velcro (NL: klittenband). “Dip and coat” is another option that is only usable in the factory.

”plait/weave” is an option that can lead to advanced designs with varying stiffness (or other properties” in direction and place. However, the production method for woven components is not easy, especially when the textile has to be integrated into hard frame parts. Another limit is that it is not easy to predetermine the shape of the end-product.

5 A “standard solution” (multi-axis) pivot at the distal end of the pylon seems a natural and satisfying solution, especially when mul-tiple distal ends can be inserted (see subprob-lem 17). However, the proximal bending point will differ from location, according to the length of the residual limb of the amputee. For this “pivot” point the “angle by deforma-tion” or “bend” solutions seem to be more appropriate. These deformations must hen be easy for the prosthetist to apply, while the pylon still has to provide weight bearing after the bending. This is a typical example of the variable-stiff conflict which makes the design of the universal prosthesis such a challenge.

6 Total contact is of utmost importance for the comfort and function of the socket.

”Following the contour” of the (unloaded) residual limb, in literature sometimes referred to as surface matching, is currently the most used method for determining the stump shape. However, due to the compres-sive forces, deformation of the soft tissue is to be expected. Deformation of the soft tissue is used in the first (3 to 6) months after the amputation to promote a stiffer residual limb, with a taper shape (see section 5.1). Also, deformation of the residual limb will not stop blood flow up to a internal (skin) pres-sure of 35 kPA (Sangeorzan et al. 1989). For posterior soft tissues in the residual limb (the calf muscle) this implies that load pressures of up to 70 kPa are allowed (Sangeorzan et al. 1989). Deformation of the limb will then be up to 5.4 ± 1.1 mm, dependent on the amount of soft tissue, it stiffness and other factors (Sangeorzan et al. 1989).

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Also, pressure cast methods deform the soft tissue, but the volume (is assumed to) stays constant. This is called volume match-ing. The “inflate/fill” option is therefore a deisgn option that promotes volume-match-ing (and a TSB socket fit). The big difference between this solution and current pressure cast solutions is that the currently pressure is applied by an apparatus that completely envelops the socket. In the presented solu-tion, the pressure is added to the socket itself. The “suck/vacuum” solution is used in the otto bock Harmony system. In this system (figure 10-1) every step is used to decrease the pressure between the socket and a spe-cial liner, thus improving the connection between them. The fit is said to be com-fortable and provides excellent control.

Tissue deformation is therefore not only a design option, but a tissue reaction to load that has to be taken into account. Also, tissue cannot be deformed to much, especially when the amputee has a bony residual limb.

7 Smart designs can further improve the weight-bearing and pressure-distributing properties of the socket.

Most professional prosthetists agree that in general, the distal end of the residual limb should not be loaded. The distal end pad (an idea that came into existence in Sri Lanka) does exactly that, but in a very con-trollable manner. It contributes to the total weight bearing properties of the socket, if the amputee has some pressure tolerance in that area. Because there is always some pistoning of the residual limb in the socket (or the residual bones in the soft tissue), the distal end pad has to be designed in such a way that it will not exceed the tolerance level during stance and ambulation. In the appen-dix, a possible solution with springs, one with elastic band and the commonly used gel pad are shown. The distal end pads should be inserted at different distances from the Pattelar tendon, because of variations in the residual limb lengths.

Extra dampening can reduce shocks and therefore decrease the amount of pressure peaks and promote comfort (also see section 4.3.5). On the other hand, the extra freedom of movement decreases the direct feedback and control over the prosthesis. In this light, vertical freedom of movement is less prob-lematic than horizontal or rotational move-ments (see subproblem 10).

Increasing the pressure (perpendicular forces on the residual limb) increases the control and can improve weight bearing. On the other hand, during swing-phase and other cases in which there is no load on the prosthesis (e.g. sitting), constant elevated pressure on the residual limb should be avoided to avoid tissue damage. Several idea’s are shown in the appendix that increase the pressure during load, but keep pressures low without the load. All these solutions react on a displacement (that is caused by the loading of the prosthesis). The “four bar mechanism” is the most basic solution of which some other presented solutions are spin-offs. The

“force redirected with pulleys”-option uses the vertical dampening displacement to increase the posterior(-anterior) pressure. This way, control is only limited decreased. However, these systems introduce moveable parts in the prosthesis thus decreasing life-time, ease-of-use and increasing costs.Figure10-1: Otto-Bock Harmony system

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8 The success of the universal prosthe-sis is highly dependent on the east of the fit-ting procedure. Several strategies can be fol-lowed to keep the fitting method simple.

First of all, use-cues can be added where use is ambivalent. Examples are the length of the total prosthesis and the socket-residual limb angle. Use-cues are tips that are part of the design. For example, by accenting the patel-lar tendon and the tibial crest on the out-side of the socket, users immediately know what the front side of the socket is. The total height of the prosthesis can be shown by tag-ging the height which the prosthesis should have when the user stands in it (mid-patellar-tendon is easily comparable with the opposite leg). Another option is to attach a temporal part that needs to be level with the top-knee height of the opposite limb when the amputee sits (figure 10-2).

Another way to improve the easiness of the fitting procedure is to standardize it. The uni-versal prosthesis will standardize it, because it will incorporate a hands-off fitting proce-dure for the socket. Further standardization can be achieved throughout the procedure by copying the fitting techniques now commonly used. These are practical and using them will improve the acceptation rate of the universal prosthesis for the current prosthetists.

Simplifying the fitting and production of the universal prosthesis can be achieved by combining them into one procedure. In this respect the “immediate production method” is similar of that of the ICEX (see section 4.3.1

– hydrostatic socket). If this can be achieved, the universal prosthesis not only reduces the need for skilled prosthetists, but also for technicians and machinery.

Quick feedback of the user will also reduce the time the prosthetist needs per client. Especially when feedback can be incorpo-rated and reacted on immediately. When the patient is loading the residual limb during the fitting procedure, it becomes directly clear when the fit is not optimal and the prosthetist and the amputee can take action by adding pressure pads, realigning the hard parts of the socket or realigning the residual limb. If this direct feedback will reduce the visits of the amputee to the prosthetist in practise, clinical tests have to determine.

Another way to increase the feedback is to make as many parts as possible transparent. If this is the case, the prosthetist can check if sensitive area’s are avoided, if all the tissue makes contact with the socket and how the tissue reacts to the pressure.

9 The advantages of promoting a tight fit during use have been mentioned while dis-cussing subproblems 6 and 7. Also rotation (displacement) can be used to achieve this. The “strangle-fit” will tighten when rotational forces are applied. Two springs, one winded clockwise and the other counter-clockwise, will make sure that rotation in both direc-tions will result in this behaviour. An advan-tage of this system is that a relatively small rotation is needed to increase the pressure. A difficulty is that spring hat to be deformed to be used for amputees with variable stump circumferences.

Figure10-2: Possibilities for adding use-cues to ease the fitting procedure.

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A completely other solution is to change the (transversal) shape of the socket. The rounder the shape, the more volume it can contain with the same circumference, resulting in lower pressures. On the other hand, the round shape is not resistant to torque. The triangular shape results in higher pressures and is far better in transferring rotational forces from the socket to the residual limb.

10 Vertical dampening can increase comfort, but also means less control (also see subproblem 7). Currently, most dampening systems are integrated into the foot. In gen-eral, the more distal the dampening system is placed, the better the experienced control will be.

11 Donning and doffing the prosthesis is an important factor in how user friendly the prosthesis will be experienced. Also, because the socket will be formed directly on the residual limb, the doffing should get extra attention. In most cases the residual limb shape will be taper (see section 3.1.3) and the socket can just be slipped of the limb (“shove”-option). However, caution has to be taken when handling bulbous shaped resid-ual limbs. In these cases the directly on the residual limb fabricated socket can get locked in.

One basic way to avoid this problem is to use a flexible socket, that when donned is fas-tened or tightened (“fix it with a rubber ring”, “tightening”, ”zip” and “belt” idea’s). In the “bend /deform” idea, the socket is elastic but the force needed for deformation is higher than the forces during ambulation. This can only be achieved when and additional device or tool is used for donning and doffing, which doesn’t fit the design philosophy.

The “roll on” idea is now commonly used in the donning and doffing of the liner. If it is applied on the socket itself, this would result in a very flexible socket and force transfer would be a problem. However, the roll on principle can be very useful during the fitting procedure, because it results in a very pre-cise total contact fit. Even while a liner can’t transfer loads, it will prevent oedema.

The wrapping solution is another idea that is very suitable for the fitting procedure. With the wrapping method, a material can be applied around all sorts of residual limb shapes. The same principle is used in the ICEX-system see section 4.3.1 – hydrostatic sockets), in which carbon fibre reinforced wraps are used, that during the fitting proce-dure are impregnated and hardened.

12 Discussed with 11

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13 The pylon has to deal with the same stiffness-deformable conflict. Does it have to change shape? Well, extra leverage acting on the residual limb should be avoided, because that implies extra pressure. Normally, that is solved by connecting the pylon to the socket at the intersection with the line of gravity (figure 10-3, compare section 3.1.4).

Another option is to use multiple pylons (see section 4.3.2). In function this last solu-tion resembles an exoskeletal prosthesis (see section 4.2.1). The exoskeletal setup is in this regard very suitable for the universal prosthesis. It provides a very stiff and strong prosthesis, while it can easily adept to vari-able residual limb lengths.

Because the universal prosthesis incor-porates a hard open-frame, the pylon will have properties of both the multi-pylon and exoskeletal solution. The basic shape used for the pylon will than be the round or triangu-lar shape.

The H-basic shape is also interesting. When two vertical pylons are connected by an addi-tional surface, a transversal H-shape will be formed (figure 10-4)

This increases the stiffness of the total struc-ture. In the same way, many connections with a stiff socket can also enhance the stiffness (“attach-surface-above” idea). This connec-tive surface can be integrated into one part by adding surfaces that can be rotated from parallel (deformable status) to perpendicular (stiff status).

14 Discussed with 13

15 To achieve a light but stiff total con-cept design, the flexible part of the design has to contribute to the total stiffness. The fitting procedure is an important factor in this.

The soft parts can add “tensile forces” to the open socket frame. Imagine this principle as elastic bands or springs between the hard frame parts. The tensile forces increase the pressure on the residual limb. As long as this pressure doesn’t exceed the threshold of the residual limbs tissue tolerance, the total stiff-ness of the system will improve.

Problematic is the variance in residual limb circumferences. If the connective bands are stretched to accommodate for bigger resid-ual limbs, the elastic bands will exert higher forces, which can result in higher pressures. Ideally, the tensile force, or even better, the extra pressure resulting from the tensile forces, can be controlled. This implies that the elastic bands can at least be adjusted in length. One fundamental problem is that (elastic) bands will always try to find the lowest force route, which results in straight lines and can result in pressure peaks on the tissue between the hard parts (figure 10-5).

Figure10-3: Moments around the socket, as a result of diffrent pylon types.

Figure10-4: H-profile.

Figure10-5: Flexible bands that connect parts will result in pres-sure peaks.

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That last property of elastic bands is some-thing that “hardening” the connective flexible parts can prevent. Of course, the flexible part than no longer generates tensile forces, but the hardened part can transfer tensile (and compressive) forces. The pressure on the residual limb is now determined by the shape and circumference of the socket. For satis-factory results with the “harden”-option, the shape has to be determined very precisely.

16 There are a few options for hardening flexible parts. Two fundamental principles both can lead to a satisfying solution.

First of all, the parts can be hard in normal circumstances and become deformable when altered. The most commonly used materi-als in which this principle is used, are plas-tics that can be heated, (de)formed and then cooled again (“freeze it” idea). A current application of these materials can be found in ski-shoes, violin supports. This are heated to approximately 60 degrees Celsius to fit the user’s body shape. This principle could be applied to the hard open socket parts, if more variance in these parts proves to increase the comfort level of the fit.

Secondly, for the flexible parts, “chemical reactions” can be used, that harden a mix of (carbon) fibres and resin, exactly in the same way currently PTB-sockets are produced.

This solution allows for a high freedom of shapes that can be given to the socket and is successfully used in the ICEX-system (com-pare subproblem 11 and 8). The big disadvan-tage of the ICEX system is that water has to be added as the reaction agent. This makes the fitting procedure a complicated and time-critical happening. Because the universal prosthesis eventually has to be fitted by inex-perienced people, this solution is not optimal. Better are solutions that can use (UV)-light, heat or electricity as the reaction trigger or reaction agent. However, these agents bring along their own difficulties, sometimes in regard to the fitting procedure, sometimes in regard to the safety of the amputee.

Other options, that require the addition (or removal) of parts or the use of specific tools or machinery (“deform it”-option), are less useable for the Universal Prosthesis. The additional parts or tools have to be included into the distributed package or kit, thereby increasing its costs.

17 The completeness of the UP is in regard to its distribution options very impor-tant.

In cycle 1 of the marketing (see section 6.3), multiple or easily interchangeable pylon ends, will make sure that the Universal Prosthesis can be used in conjuncture with existing feet. For cycle 2, a foot has to be part of the distri-bution kit.

The suspension system (see section 4.3.4) is another integral part. Suction suspension is regarded as the most comfortable option nowadays. It does demand a highly accurate fit of the socket.

Knee straps or suspension sleeves are some-what less comfortable during the donning and doffing of the prosthesis, but provide excellent suspension.

Figure10-6: Suspension sleeve

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Problems arise when the suspension is to loose and the residual limb starts pistoning in and out the prosthetic socket.

Supra-condylar and supra-patellar sock-ets (section 4.3.4 – anatomical suspension) enclose the hard parts of the residual limb and the knee. This suspension “cups” are stiffly connected to the socket. In current condyle suspended sockets, such as the KMB, the suspension parts are integrated into the (high) socket.

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10.3 idea selecTion and inTegraTion

Having discussed all these possibilities, those who integrate well into a total design have to be selected.

In section 6.2 it became clear that the socket has to exist of both hard and soft parts and that it will at least contain an open-frame socket that can provide weight bearing for the amputee. This open-frame socket can at least partly morph into a multi-pylon / exoskeletal pylon (as discussed in subprob-lem 13/14). The pylon can end in a multi-pur-pose connection component (subproblem 17). Alignment can be improved if this component can be rotated (subproblem 5). To attach the frame parts, (elastic) bands or belts can be used (subproblem 1, compare subproblem 15/16) but it has to be possible to adjust them precisely in length. More distal the length of these bands has to vary more, because of different residual limb shapes. Velcro can be used to attach these bands. Velcro is com-monly used in orthopaedic appliances and a blood pressure meter (sphygmomanometer) illustrates that the connection can cope with medium-high pressures (200 mmHg = 26,6 kPa) of the connective area is big enough.

For the fitting procedure of the hard frame, this results in figure 10-7.

In contrast to the open-frame principle, every area of the residual limb should make contact with the socket, to prevent oedema (see sec-tion 3.1.3). This can most easily be achieved by rolling a highly flexible and stretchable textile or material on the residual limb, as is currently done with liners (subproblem 11). If we can harden this flexible material (subprob-lem 15,16) or fill the space behind it (subprob-lem 15), the total contact surface can become weight bearing and thereby increasing the comfort level of the socket. In this case, pressure has to be applied onto the mate-rial that will become rigid and the residual

limb, because else the socket becomes shape matched instead of the preferred volume matched (subproblem 6).

To achieve this pressure casting, the outer and inner layer of the socket with a material that will become hard after filling and apply pressure. The outer layer of the socket can also exist of a roll-on component. To avoid deformation on the outside, the outside layer needs to be either very stiff or restricted. For the Universal prosthesis, this restriction can be achieved by simply wrapping the outside with difficult to expand material or textile.

For the fitting procedure of the soft socket, this results in figure 10-8.

Figure10-7: Steps for fitting the hard frame Figure10-8: Steps for fitting the soft frame

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The two fitting procedures have to be inte-grated into one, resulting in figure 10-9.

Figure10-9: Steps for fitting the combined system

10.4 evalUaTion oF The inTegraTed design and conclUsion

If we quickly evaluate the resulting proce-dure and design, we see that the total has high potential to achieve that:

- The fitting procedure is a hands-off method which combines the best of the TCB and PTB principles.

- The fitting procedure is suitable for a wide range of residual limb shapes. The range is primarily dependent on the shape of the open-frame parts.

- The resulting prosthesis is not too heavy, not bulky, comfortable and siff.

The distribution kit will contain at least 2 or 3 hard frame parts, several Velcro bands, a special fabrication liner, an connective com-ponent, a filler (material), a means to apply pressure to the inside of the socket while hardening, wraps. The only tool needed is a saw, which is widely distributed and accessi-ble.

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comParison

This intermediate design can be scored against the commonly used PTB-procedure and the ICEX-system (table 10-1):

discUssion

If the currently presented fitting procedure can be realised, the Universal Prosthesis is very comparable with the ICEX-system in performance. This is not so surprising because the ICEX-system is also a hands-off fitting method (and also needs a compres-sive device). However, the ICEX-system is not to suitable for inexperienced prosthetists, because pressure-pads have to be applied by the prosthetists on pressure sensitive area’s and the wrapping of the residual limb (and pads) is difficult.

The Universal prosthesis has some other advantages. It is fitted with the amputee standing and it uses the PTB-principle, thus using pressure tolerant area’s to a much better extend. These two features will very probably lead to a more comfortable fit (espe-cially during stance). Clinical test will have to prove this in practise.

Criterium UniversalPros.

ICEX StandardPTB

Mainargument/comments

1Universal ++ + + The UP combines the best of two worlds, because it’s a PTB-TCB-hybrid.

2Comfortable ++ + + (needs clinical test)

3Easilyfitted ++ + - UP has many steps, but ICEX requires knowledge to apply pads, apply wrappings and steps are time-critical

4Controllable + + ++ PTB can be adjusted better after the fitting procedure.

5Usable 0 0 0 The PTB might not need a cosmethic cover, because it is an exoskeletal design.

6Safe + + ++ There are no problems expected, but PTB is used for many years by now. PTB normally produced with toxic resins.

7Affordable 0 0 0 Dependent on the costs of personel and the tools needed such as a compressor.

8Cosmetic 0 + + (needs to be improved)

9Quickfitted + + - PTB needs many steps.

10Distribution + + - PTB needs specific tools

Table10-1 Quick comparison between the Universal Prosthesis and two popular fitting systems.e

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11concePt

Having determined the global design and fitting procedure, the final shape and the properties of each part have to be chosen. The final design evolves over multiple cycles, because each change in a part influences other parts. Hereafter the most important design considerations for each part are dis-cussed, but not (necessarily) in chronological order..

The hard open-frame socket parts (section 11.1) are the base of the design. They are the parts of which the most clear idea about how they should look exists, because they evolved out of the designs made in Sri Lanka and it became clear what improvements were needed in the analysis.

The best argument against an open-frame socket design (that total contact is needed to prevent tissue damage and oedema), is solved by adding a soft socket (section 11.2).

The pylon (section 11.3) is the connection between the socket and the foot (and indi-rectly to the ground). Especially the connec-tive component at the distal end is important. It is needs to connect the hard socket to the foot while providing an air-tight seal for the soft socket.

11.1 The hard sockeT

11.1.1 selecTion oF loadable and avoidable area’s based on anaTomy

The open-frame socket has to make contact with the pressure-tolerant areas of a variation of residual limbs. The variance in circumfer-ences and lengths of these residual limbs can be found in appendix G. As emphasized in section 3.1.3, these measurements where taken in Sri Lanka. Amputation procedures in developed countries are somewhat more standardized, resulting in a lower standard deviation. However, residual limb lengths in developed countries will vary from 100-180 mm, quite comparable with the data gath-ered in Sri Lanka. It is clear that the first 100 mm from (mid) patellar tendon are the most important for the open-frame socket. Luckily, the variance in circumference is also the smallest around that area. At 50 mm from mid patellar tendon the P5-95 spread is 230-340 mm). At 150 mm distance from mid patellar tendon, the circumference can vary from 170-320 mm. That apart from the fact that many amputees will have a shorter residual limb length (and no circumference at all).

Having redesigned the parts, the resulting fitting procedure (section 11.4) needs to be optimized. Incorporating a low-expertise fit-ting procedure is the unique selling point of the universal prosthesis and therefore it has to be solid (no buyers means no product). The user-friendliness of the design is discussed in section 11.5 (no satisfied users means no buyers). The high-tech design that is the result has to be produced in such a way that, in time, the universal prosthesis becomes affordable for a broad group of users around the world (section 11.6).

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In appendix R, this data is combined with the anatomy of the residual limb (overlay 1 to 4). Overlay 5 shows the resulting spread in pres-sure sensitive and tolerant areas. The bony prominences are the most important factor in determining these areas. These were scaled in respect to the circumference variance (P5-P50-P95). It has to be noted here that these areas are estimations, because in reality the anatomy of everybody differs. It would be far better if the data would be obtained from (scans of) a large amount of residual limb shapes and measured tissue properties. However, that information is not available in literature and time-consuming to generate. The estimation here is reasonable and makes use of the same assumptions as prosthetists do while fitting a prosthesis.

Interpreting the data from appendix R, over-lay 5, it becomes clear that there are quite some areas that overlap (mid patellar tendon taken as a fixed point). The pressure sensi-tive area’s are shown in red and don’t domi-nate. The big blue and green area is loadable. This results in overlay 6, where the loadable and avoidable areas are selected. The chosen areas are shown till approximately 130 mm from patellar tendon, after which they fade out, in conjuncture with the variable residual limb length.

11.1.2 deTermining The roUgh Frame shaPe.

Having selected the loadable areas, the interface frame that will transfer the load to the residual limb have to be materialized. The bigger these parts are, the better the pres-sure distribution will be. The smaller these parts are, the better they will be adaptable to accommodate for the wide range of stump sizes and shapes.

On overlay 7, an estimation of the maximal load that can be carried by the soft tissue is given. Every surface has a maximum pres-sure tolerance, an area (size) and an average angle in respect to the gravitation load line of the total body mass. From these, the maximal upward force is calculated.

Note that the Free Body Diagram shown is not in equilibrium. The current forces will coerce the soft-tissue to deform and the residual limb to rotate and trans-late (if the socket is regarded as fixed in space). Also, resulting shear stresses are not taken in account. However, this behav-iour cannot be predicted without more knowledge of the (properties and shape of the) frame parts. It is assumed that the user will compensate for pressure overload and that the maximum upwards force will not diminish significantly by the relocations.

It is concluded that the interface surfaces of the frame will have to be maximized to ensure a comfortable fit during the fitting procedure.

The preferred area’s of load as presented in overlay 7, lead to the frame parts as shown in overlay 8, shown in blue. These parts will form the interface to the residual limb and still need to be connected by a stiff frame that is able to transfer the loads between the interface parts and to the ground (overlay 9, shown in red).

The interface frame can be some what easier deformable to fit the varying residual limb shapes. More distally, the variance is bigger and therefore the parts have to be better deformable there. To maximize contact, mul-tiple strips downwards are chosen where possible. Near the patellar tendon and on the opposite side (posterior), the variance in residual limb shapes can be compensated by translation of the frame.

This stiff frame can be translated because of two vertical areas where no frame is present. This effectively splits the frame into two parts.

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Tensile forces (that need to be transferred from the anterior from the anterior to the posterior to prevent the parts to part and the residual limb to slip downwards) are trans-ferred by belts of connective textile, shown in green in layout 9.

Layout 10 summarizes the tough frame design. The belts can be fastened by a tight-ening mechanism or by Velcro. The space in between the frame parts is filled with carbon or glass fiber textile, which will help to strengthen the connection between the parts after hardening of the soft socket (see section 11.2). The stiff frame parts are lengthened so that they will function as a pylon. For small amputees, these frame parts can be short-ened by sawing the distal end. A connective part (see section 11.3) is added to connect the foot.

11.1.3 oPTimizing The Frame shaPe in regards To The anaTomy.

Having determined the rough shape of the frame parts, these have to be (re)matched to the anatomy of the residual limb.

In overlay 11 this process is shown. In the top row, slices from the “visible human project” are given at steps of 10mm, from the patellar tendon, to 130mm distal.

These slices give a good impression of the bone structure of the residual limb. As a reminder:

- Bony prominences (with only skin over them) cannot be loaded.

- Muscle with bone “behind” it can be loaded well, but perpendicular.

- Large areas of muscle can be loaded well, but deformation has to be restricted.

The general shape of the bones is shown in black. Muscle that borders these lines can be loaded (perpendicular). The green lines indi-cate where the stiff frame can part. Variation in residual limb circumference can be com-pensated by moving the green lines together or away from each other.

Tensile parts (straight lines between them on the border) will not result in tissue damage.

In the second row, the cross-sections of the rough frame design from layout 9 are shown. These are used as a guide to determine the optimised shape.

To stabilize the forces resulting from pres-sure on the inside of the frame, the support-ive areas and stiff frame parts need to be divided as good as possible over the circum-ference.

Having tree strips downwards this means that midpoints of the strips have to be equal distance from each other (an isosceles trian-gle).

In row 3 this has been pursued, without neglecting the tissue pressure tolerance. The V-shape of the anterior part is to protect the tibial crest. The patellar tendon indent can be easily recognised in blue (at PT-height).

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To prevent the limb from slipping through the frame near the distal end, the anterior strip and the medial strip get closer together near the end. This is in line with the higher distal forces during gait in anterior-poste-rior direction to compensate the then acting moments and the higher force to compensate for the moment caused by the load on the patellar tendon (see section 11.1.5).

In row four, these strips are connected proxi-mally to bridge over and protect the pressure intolerant areas. Also, the stiffness of the stiff frame parts is added to maximise the contact area with the residual limb. Where necessary, direct contact with the hard borders of the stiff frame is countered by overlapping the soft frame with the interface frame.

In row five, the frame is optimised for the variance in residual limb circumferences. The more flexible blue parts that are not sup-ported or attached to the stiff frame are given a curvature that is equal to that of P5. These parts also bend in more distally, to extra sup-port smaller residual limbs.

11.1.4 back To 3d

The optimized cross-sections from Appendix R, layout 11, were stacked together in 3D, resulting in figure 11-1.

They were connected and a little smoothened. This was necessary because the slices from the “visible human project (see layout 11) proved not to be well centred.

The result is as seen in figure 11-2 and appendix R - layout 12,

Figure11-1: 13 stacked layers that where derived from the anatomy of the residual limb. Top view and isomet-ric view.

Figure11-2:Together with the resulting frame parts. [Top] stiff frame, two views. [Below] interface frame.

supra condylar brims

for aligning the cross-sections.

some cross-sec-tion placements needed to be adjusted. The slices from the visible human project where not aligned before processing.

basic shape of the pylon.

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Note that the tensile textile (see layout 10 and section 11.1.2) has been replaced by extensions of the frame parts. These exten-sions are thinner and more flexible as the rest of the stiff frame. They are connected to the opposing frame by Velcro. This improvement was made to ensure that:

- the frame parts are on the proper height in respect to each other

- there will be some curvature of a straight line, improving comfort.

- assembly is quicker because there are less parts.

The most distal end of the stiff frame strips has been punctured to enable the connection of the connective component on the desired height.

Technical drawings of the frames can be found in appendix Z.

11.1.5 maTerial choice

To assess the mechanical properties of the frame, first the material has to be specified.

maTerial oF The inTerFace Frame

For the interface frame (blue) a plastic will be used. It should be possible to deform the interface frame to fit the varying residual limbs, but it should also be able to transfer some forces. Solution to this contradictory is found in deforming the plastic by heating it, and then fix it into the desired position while cooling down. This should be possible with normal heating equipment, so the soften-ing temperature should not be higher than 150°C. But it also should not deform at a tem-perature lower than 50°C, as it might turn soft during use in the sun on a hot day.

Several, commonly available plastics are suitable; PP, PVC, PS, ABS, PMMA, POM, PPO. PVC is toxic for the environment and will therefore not be used. POM and PPO have softening temperatures which are quite high, 155°C and 130°C respectively. It would be possible to use them, but there are other pos-sibilities with lower softening temperatures (table 11-1).

ABS was chosen from those four, as it is said to have good chemical and mechanical prop-erties. Examples of applications are security helmets and profiles for skis and surfing boards.

PP PS ABS PMMABendingstrength(Nmm2) 40-115 80 55-80 140

Modulusofelasticity(N/mm2) 1250-2200 2600-3200 1800-2500 3250

Softeningtemperature(C) 90 100 90 115

Table11-1:Four material options for the interface frame.

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maTerial oF The sTiFF Frame

For the stiff frame (red) Hylite, a composite material developed by Corus) will by used. This is a sandwich material, existing of two aluminium layers with a plastic layer (poly-propylene) in between. It is a very lightweight and strong material. At a thickness of 1.2 mm it has the same flexural stiffness as steel at 0,74mm and aluminium at 1.06mm, while having a much lower mass.

When the aluminium layers are grinded or machined, hinges can be formed as is shown in figure 11-3. It can also be formed in the desired shape by deep drawing as shown in figure 11-4.

Other options are:

- Carbon fibre reinforced resins- Aluminium- Titanium- Glare

11.1.6 mechanical ProPerTies

The mechanical properties of the frame can be assessed in several ways. The best way is to build the frame and to experiment. However, production of several parts of the frame is expensive.

With the material properties of Hylite and ABS known and the frame design available as an 3D model, the behaviour of the parts under load can be simulated (finite elements methods).

Many studies to socket fit and socket deformities were conducted in literature. These in-depth studies were demanding and the shear and stress forces in the total socket

or in the residual limb were assessed. In this stage of the development these specific FEM-models are too time-consuming. Instead, a quick indication of the stresses during stand-ing on the two force conducting frame parts (red frame) and on the connective compo-nents (strips & Velcro) between these frames is given. The applied loads were chosen as shown in appendix S - FBD.

Appendix S - FBD shows the main resultant forces when standing with 50% of the body weight (100% of the load on the prosthesis) supported by the patellar tendon. It again illustrates (as in section 3.1.4) that the PTB-bearing principle increases the loads on the anterior distal end and the posterior mid of the residual limb. For people with sensitive distal ends, this can be a problem. In that case, a TCB-approach is more suitable (see section 11.2).

The 3D-application of thise forces and the frame’s displacement behaviour can be found in appendix S - FEM.

Figure11-4:Deep drawed car part from Hylite. (source: Corus)Figure11-3:Applying hinges to Hylite (source:

Corus)

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What we can conclude is that with the cur-rent thickness (2 mm) and shape, (Hylite and) aluminium has such a stiffness, that major deformations can be expected. Solutions can be found in applying ribs, thickening the structure or increasing the area of the frame parts. Also, the residual limb will constrict the total amount of deformation. And, as can be seen in figure 11.2, the general shape that follows the anatomy of the user will not change much, thus staying comfortable while deforming.

The socket/pylon in this shape is not suitable for prolonged ambulation. Because of its free-dom to move, it will become subject to fatigue and break. However, the addition of the soft socket will improve this.

11.2 The soFT sockeT

The soft socket exists of a flexible closed tube or “fitting liner”, that will become the inner and outer layers of the prosthesis, and the filler that will harden in between these layers (also see 10.3).

11.2.1 FiTTing liner

The fitting liner is rolled on to the residual limb and, after placing the frame parts, rolled down over them again. It will function as the inner and outer layer of the prosthesis. These fitting liner will envelop empty space and the frame parts. The resulting inner space or chamber will be filled with a filler or foam.

The material choice of the fitting liner deter-mines most of its properties. In its relaxed form it has the smallest circumference. Because it has to fit around the connector and the frame this minimal circumference is about 200 mm. While rolled on to the knee or even higher, it has to be stretched to at least the p95 maximal circumference (at 25 mm proximal from patellar tendon), which is about 370 mm (see appendix F) and, when taking a maximal thickness of 10 mm of the socket in account is about 430 mm.

Because the fitting liner will be the outside of the prosthesis, it also makes contact with the skin and the environment. Resulting in the following requirements:

- The material has to be able to lengthen more than 215% in transverse direction.

- The material has to be non toxic / non-irritat-ing.

- The material has to be smooth and repel dirt.- The material has to resist impact.

One possible material is a combination between PP and PU. PU (on the inside) will stretch easily (up to 500%) and will integrate with the PU-foam (see later this section). PP (on the outside) will be smooth and non-irri-tating. If necessary, for example when the amputee has work that is very demanding on the prosthesis, the outer layer can be coated (with for example epoxy resin) to increase impact resistance.

The fitting liner can be tube-shaped, but has to have a padded distal end to overcome high distal-end pressures. This is common for most liners.

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11.2.2 The Filler maTerial

eFFecTs oF Filling

Filling the space inside the prosthesis will contribute to the stiffness of the whole. However, to contribute significantly, the foam has to have stiffness in the same order as that of the load bearing frame. Foam that will have this type of stiffness is often very brittle and in that case, the inside would deteriorate with use. Filling the inside with foam can best contribute to compressive forces (in between the frame parts). However, weight-bearing will result in the frames wanting to part and thus in tensile forces.

A completely other advantage of filling the prosthesis is that it will contribute in weight bearing. The prosthesis will effectively become a total contact bearing socket (TCB). Without pressurizing the foam (0-5 kPa), this would already prevent oedema. However, with higher pressures ranging from 30-40 kPa (50% TCB-behaviour) to 60-80 kPa (100% TCB-behaviour, comparable pressures as used in the hydro-cast and ICEX methods), the socket will contribute more and more to the weight-bearing properties of the total.

resins

The space within between the layers of the prosthesis can also be filled with resins. When combined with fibres, the result can be very stiff and strong. In the case that resins are used, a suction method as is commonly used while fabricating prostheses (resins applied from above, air sucked out below, so that the resin will divide through the space) is preferred. In that case, the inner space of the prosthesis is minimized and the increase in weight will be minimal.

PolyUreThane

Foams have some special properties that are useful in prosthetics:

- It has a very good mass-volume ratio- It can take make shapes- It is available with a great variation of proper-

ties, including mass, rigidity /stiffness, yield strength, etc.

Polyurethane is one material that is easy to foam and is available for a broad range of applications. Polyurethanes and derived plastics are used in PUR-foam, but also in dashboards of cars, for cushions in seats and chairs, for shoes (soles) and in other flexible, semi-rigid and rigid applications.

Polyurethane can be used in the universal prosthesis if a mix can be found that meets the following requirements.

- It connects to the frame parts and the outer layer of the prosthesis

- It does not grind to powder (wears) under dynamic load

- It divides itself well within the prosthesis.- It reacts slow enough, so that the pressure

can be homogenous increased. But within 10 minutes, so that the fitting procedure stays comfortable

The application examples, especially the use in shoes, show that PU can meet these requirements. Its use in aerosol sprays, such as PUR, makes it plausible that it also can be distributed in a spray. It can use water (a component of air) as the reagent (in a spray the reacting chemical components of poly-urethane are prepared in a special way) and use the air in the chamber in the prosthe-sis as the filling gas. It is no problem when the reaction increases the inner pressure, because this is an effect that is wanted for weight-bearing anyways.

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To optimize the properties of the universal prosthesis, the choice of foam is very impor-tant. Because the application is very specific, it is probably a better option to develop a “new” foam in corporation with a producer of PU.

Fibre reinForcemenTs

Even when instead of resin PU (foam) is used, glass or carbon fibres can enhance the stiffness of the prosthesis. Note that the bot-tleneck is the connection between the fibres. However when the connective material (foam) would strain 25% when a certain force is applied, the distance between the two attach-ments of the material to the stiffer compo-nents becomes critical in the stiffness of the whole, as explained in figure 11-5.

This principle can be used by applying thin extensions of carbon or glass fibres to the weight bearing frame parts as shown in figure 11-6.

In this example, the (massive) PU layer can be stretched up to 500% of its original length, where no fibres are integrated and can not be stretched where the fibres are integrated. The two layers can slide along each other. The foam will “glue” then together and a much stiffer connection is obtained than when the foam or PU directly connects the frames.

Figure11-5:Less space in between the frames is better; it results in a stiffer prosthesis.

Figure11-6:A Polyurethane layer is partly rein-forced with fibres. The Hylite is milled to better attach the reinforced PU. The two Polyurethane layers can slide along each other

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11.2.3 adding PressUre

When the chamber is filled with foam, pres-sure has to be added before it has taken its final form. This can be achieved in several ways:

- Using the pressure from the aerosol spray, at the same time injecting the foam. Current sprays have a nozzle that will vaporize the contained liquid. In this application, the nozzle is not necessary and the needed pres-sure can be directly added to the prosthesis.

- A mini hand pump or compressor- A separate CO2, N or air spray or gas patron.

The volume that needs to be filled when a residual limb of length 100 mm and a maxi-mal socket height (430) is fitted is estimated to 1.5 litres. To apply a pressure of 0.8 bar (80 kPA) to such a volume, the following gas patrons can be used: 0.97 litres at 2 bar, 0.36 litres at 4 bar or 0.16 litres at 8 bar.

- A compressor.

11.3 The connecTor

The connector has several important func-tions in the design. It has to:

- connect the weight-bearing frame parts.- connect the frame to the foot.- be adjustable in height.- be airtight.- be stiff.

connecTion To The Frame

Because the frame parts will be completely surrounded by (foam) and the outer layers they can contain holes. There are two basic options to connect the frame parts to the connector. One is with screws and the other is without.

The use of screws is chosen for safety rea-sons. A disadvantage of this system is that it results in that the prosthesis can only be lengthened or shortened in steps. This can be solved by adding an extra lengthening com-ponent between the foot and the frame.

Using the spray is the preferred solution in situations where only a few prostheses are fitted. The spray is easily distributed and relatively cheap. In situations where more prostheses are fitted, such as an orthopaedic workshop, a compressor can be cheaper and more environment friendly.

Figure11-7: The airman Panter is an example of a hand-pump.

Figure11-8:Two ways to connect the frameparts. Because all mayor forces between the frame and the connector work in vertical direc-tion, fitting of the frame on just shape is sufficient (left). However, to be sure the frame parts connect well, also during ambulation, and the connec-tion is airtight, screws can be added (right). Both solutions are cheap, intuitive understandable and position the posterior and anterior frame parts on the right height from each other.

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connecTion To The FooT

The connection to the foot is a standard pyr-amid alignment core (see Appendix M) that is commonly used. When screwed in tight, it can be removed with a tool and replaced with another alignment core when necessary. To resist the torque that acts upon it as a result from turning (the foot), it is better when it is attached permanently (figure 11-10). In the latter case, transition extensions to other systems can be made available, possibly inte-grated with the extension as shown in figure 11-9.

airTighT

The connector has to seal the inner chamber of the prosthesis, while allowing the frame to protrude.

Figure11-9:An extra component that can fine-tune the length enhances the adjust-ability of the prosthesis.

Figure11-10:The connection to the foot is achieved by either screwing a standard pyramid alignment core into it (changeable) or by integrat-ing the alignment core in the piece (improved strength). The dome increases the range in which the foot can be aligned.

Figure11-11:(Up and Left) The airlock is achieved by an outer and an inner seal. NOTE: The dome on the connec-tor is drawn on the wrong side!

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The airlock can be made from two seals. The first seal is made from a compressible rubber or plastic, and will be placed on top of the connector and between the connector and the frame parts. The second seal is placed over on the outside of the connector and the frame parts. This part is made from an elas-tic and compressive material. Its elasticity is used to generate the force that is needed to keep the whole airtight, even when apply-ing the maximum pressure (80 kPA) and the compressibility to fill height differences and filleted corners.

Fill channel and valve

Because it is the only place where the outer layer is interrupted, it is also the perfect spot from where to inject the foam and apply the pressure. To achieve this, a channel that con-nects the outside with the inside is drilled in the corner of the component (figure 11-12). For safety, a Minivalve is added. These valves are mass-produced and very cheap (figure 11-13).

noTe on alignmenT

In current endo-skeletal prostheses, not only a distal alignment core, but also a proximal alignment core is added. The universal pros-thesis only uses one alignment core (dis-tally). One would expect that this results in reduced possibilities for alignment. However, traditional endoskeletal systems did not incorporate a proximal alignment core. The placement of the connection to the pylon was determined during the fitting proce-dure. In practise, this went wrong so often that an extra alignment core was added to the system. In the universal prosthesis, the socket and pylon are integrated and the alignment between them cannot go wrong! The distal alignment core provides sufficient adjustability.

Figure11-12:The fill channel and the valve in the connector. To transfer the filler up to the proximal side of the pros-thesis, flexible tubes (straws) and splitters can be used. The entrance of the channel has to be distally or on the bottom of the connector, because else the air seals would be in the way.

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The placement of the residual limb in the socket will determine the right alignment. This placement will only be problematic in (the few) cases where contractures are a prob-lem. In those cases, the pylon can be short-ened (at 260 mm from patellar tendon) and a normal pylon can be attached with standard screw connections as seen in appendix M).

11.4 resUlTing FiTTing ProcedUre

The fitting procedure doesn’t change funda-mentally (see section 10.3). With optimized components it adds up to the figure in appen-dix U and the following steps:

siTTing1) The foot is connected to the connector.2) The user rolls the fitting liner that will

become the outer layer of the prosthesis, onto his residual limb and up to his thigh or knee.

3) The needed length of the prosthesis is meas-ured with the frame parts and the connector. The height of the total has to end on top knee height.

4) The frame parts are attached to the connec-tor. The connector is already distributed with the inner air seal and straws attached (see section 11.3), so the connection is immedi-ately airtight. The needed screws are included in the distribution kit (TOOLS NEEDED: SCREWDRIVER).

5) The frame parts are placed on the residual limb.

sTanding6) The frame parts are connected to each other

and the user can stand in the prosthesis. The Velcro can be detached and reattached until the user can stand in the prosthesis (50% of

his body-weight on each leg) without sliding down, while experiencing the most satisfac-tory fit. If the prosthesis seems too long or too short, the connector can be re-adjusted. If specific areas are painful, gel pads can be added or the interface frame parts can be adjusted by heating and deforming.

7) It is made sure that the supracondylar brims press against the knee (see section 11.5).

8) The prosthesis is taken off the residual limb (doffed) and the distally extending frame parts are sawn from the prosthesis. (TOOLS NEEDED: SAW)

9) The straws inside the prosthesis are cut on to the right length (10-20 mm from the upper border of the frame parts).

10) The prosthesis is donned again and the fitting liner is rolled down, over the frame parts.

11) The outer seal is pulled over the connec-tor and the fitting liner. The extending liner parts are cut off (TOOLS NEEDED: KNIFE OR SCISSORS).

12) The prosthesis and the knee are wrapped (tight) with wrapping bandage.

13) The foam spray is attached to the connector.14) The foam is injected.15) The pressure is increased till a comfortable

level is found or the maximal pressure of 60-80 kPa is reached.

16) Waiting 10 minutes.17) The wraps can now be taken away.

Figure11-13:An example of a Minivalve (source: www.minivalve.com)

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2) The second, more expensive solution, provides an easier to use and in cases where pistoning is a problem, more comfortable suspension. This option can be used for people who are sensitive, have less force, have problems with pistoning or whose anatomy doesn’t allow for supracondylar suspension with the integrated brims. Before the donning of the prosthesis, the user has to roll on the liner with the pin threaded in. The pin has to be positioned well, because it has to lock in the shuttle.

3) If the integrated brim solution fails, and finances are limited, a very functional and quite comfortable (except in some case where knee flexion (sitting) results in high forces in the popliteal space [Seymour 2002]) solution is the knee cuff.

Suction suspension might be integrated in the system in the future.

cleaning & cosmeTics

Whether or not the prosthesis is cleanable is mostly dependent on the outer layer (see section 11.2). An extra outer layer could be applied that makes cleaning easier. This extra layer could also function as a cosmetic transi-tion from the pylon to the foot (add an ankle shape) and make the pylon more oval shaped.

walking18) The user can now walk around. The align-

ment of the foot can be adjusted when neces-sary.

11.5 daily Usage & sUsPension

The universal will basically be used in the same way as currently available prostheses (see section 4.3.4). Most important aspects of use are donning/doffing, suspension and cleaning.

sUsPension and donning/doFFing

Suspension can be achieved in three ways:

1) Standard supracondylar brim suspension. The integrated brims on the interface socket make contact with the knee at the broadest part of the fibular head (see figure 11-14). The variance in this distance from patellar tendon is expected to be small, so the brims can be fabricated on a predetermined length.

2) Shuttle lock suspension. In this suspension type, a shuttle lock is added to the standard fitting liner and an extra liner is rolled on before the fitting pro-cedure with a pin or plunger threaded into the distal end of the liner (compare figure 4-32). The shuttle has to be unlocked before doffing, so a button needs to be brought to the outside of the socket. One possible solution is shown in figure 11-15 (next page).

3) Supracondylar cuff suspension or suspension sleeve. A cuff or belt is attached to the finished prosthesis. A suspension sleeve can also be attached.

The suspension types result in a different donning/doffing approach

1) In the standard (supracondylar) solution, the residual limb slides, while pushing the brims slightly apart, into the prosthesis. When the user has to little force to do so (for example elder), or when the condyles are too sensitive, a hole can be made in the prosthetic socket after the fitting procedure. Through this hole, a sock can be pulled, which assists in the donning of the prosthesis. The hole has to be finished to protect the (rigid) foam that will otherwise wear too fast.

Figure11-14:Height of supracondylar suspen-sion.

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11.6 ProdUcTion and Price

Warning: Keep in mind that the estimations in this section are quite rough.

The production price and production method is dependent on the amount of produced parts (production volume). Estimations are made for 1000 and for 10.000 pieces. For this relatively low amount of pieces produced (per year) the production can be out-sourced. The estimated prices can be found in appen-dix V.

11.6.1 ProdUcTion cosTs Per ParT

inTerFace Frame The interface frame exists of two parts, each in a left and right version. The frame parts can be made by cutting and deep drawing. When higher quantities are produced, the frame parts can be injection moulded.

weighT-bearing Frame

The Hylite, used for both the higher and lower production volume, is relatively expen-sive, but easily processed.

FabricaTion liner

The basic version of the production liner for the universal prosthesis (without pin/shut-tle suspension) uses a simple tube on which a distal end pad is welded together by sonar heating. The distal end pad is made of sili-cones.

connecTor For the lower quantities, the connector is milled and drilled. For the higher quantities a redesign might lead to a decent solution that can be injection moulded (in high qual-ity plastic, ceramic or aluminium). The inner air seal has to be produced, other parts are bought in.

disTribUTion kiT

In the kit, that protects the parts, extra com-ponents can be found, such as manuals, gel pads and a sock (also see section 10.4).

Figure11-15:The shuttle for the pin/shuttle suspension can perforate the outer layer. The rings will restore the system to an airtight state. The shuttle can be attached on most heights (with varying circumference). During the fitting procedure the pin is locked in the shuttle.

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This results in a production cost price of 110 (at 1000 pieces a year) to respectively 55 (at 10,000 pieces a year.

11.6.2 develoPmenT cosTs

It is clear that the costs of developing the universal prosthesis will be primarily made of developing costs. The way to a market-ready product is long. Among others, to make the prosthesis ready for the first market (cycle 1 section 6.3), time (FTE’s in brackets) should be invested in (also see chapter 13):

- (1) researching the pressure tolerance of the residual limb.

- (2) collecting data about residual limb vari-ances, including bone-shape and soft tissue properties.

- (2) development and selection of the right materials.

- (2) optimizing the design of the components and parts.

- (4) clinical trials.- (2) re-evaluate and improve business-setup

and distribution strategy.- (1) project management.- (3) project office support.

11.6.3 markeTing and disTribUTion cosTs

Marketing will make the universal pros-thesis a well known alternative for the prosthetist. Sales and services are needed to distribute the product.

markeTing

The marketing, especially for the first cycle, has to be pro-active and direct. The buyers of the universal prosthesis are well known (prosthetists, orthopaedic workshops, hos-pitals, etc), so the campaign can be reason-ably focussed. On the other hand, the end-users or amputees need to be informed as well, because they might opt for the universal prosthesis while choosing the prosthesis that will be fitted. Also, they have to know the uni-versal prosthesis is available for them in the case they need a spare one.

This would imply that a team consisting of about 17 full-time workers could launch the universal prosthesis in one year. With a FTE price (including accommodation, etc) of 47,000 Euro a year, the first cycle costs would add up to 800,000 Euro. If 1000 universal prostheses are sold for a period of 5 years, this would be a 160 Euro increase of the cost price of the product. For the next cycle (world market), another development round of the same magnitude (800,000 Euro)is expected to be needed, resulting in an increase of 14.5 Euro a piece (over 11,000 sold prostheses a year).

This results in a R&D and production cost price of 370 and 70 Euros respectively.

The R&D prices can be lowered significantly by intensive collaboration with big orthopae-dic producers (who have a lot of knowledge in-house and who can divide the R&D-costs over multiple products), and by attracting grants and subsidies.

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For the second cycle, the initial buyers are even better known (local workshops and hospitals) and distribution or collabora-tion with expert NGO’s, such as the World Health Organization and the Cambodia Trust Foundation has to be sought. A budget for both marketing campaigns has to be reserved:

Cycle1: 100,000 Euro, resulting in an increase of 100 Euro and a total price of 470 Euro.

Cycle2:100,000 Euro, resulting in an increase of 9 Euro and a total price of 79 Euro.

sales and service

The service has to be good, because this is an important source for feedback. Feedback will reduce design cycles and R&D-costs. Also, it is the most important factor for a good cus-tomer base.

Cycle1:4 FTE at 50,000 Euro a year, resulting in an increase of 50 Euro and a total price of 520 Euro.

Cycle2: 6x4 FTE at a mean of 25,000 Euro a year, resulting in an increase of 55 Euro and a total price of 134 Euro.

11.6.4 conclUsion

Keeping in mind that the estimations in this section are quite rough, the expected costs stay well within the requirements. For both the prices (European/US and World market) the R&D-costs are significant, but there are possibilities to lower them by attracting grants and by choosing the right business-partners. Delivering a quality product will result in lower costs on the long term, so cut-ting down on the input in research is not an option.

For the world market product, collabora-tion with NGO’s such as the Red Cross, WHO, Cambodia Trust Foundation, etc can further lower the price. Costs of this product are made up from service and sales for 40% and from marketing costs for 7%. Collaboration with well organized NGO’s can reduce both costs significantly and the costs price of the Universal Prosthesis could fall under 100 USD.

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12evaLuation

The concept as presented in chapter 11 can be evaluated in several ways:

1) Review it against the criteria (section 7.1). 2) Review it against the requirements and the

additional goals (section 7.2-7.5).3) Review it in comparison with other prosthetic

systems for transtibial amputees.4) Have it reviewed by professionals (experi-

enced prosthetists).5) Build a model and evaluate the design by

inspections6) Build a working model (prototype) and try

that out in practise.

In section 12.1 evaluation method 1 and 3 are taken together and a discussion with the requirements as a guide (method 2) is added in 12.2.

In section 12.3 a model is presented that was build. This model can be used for assess-ing the shape of the frame parts (evaluation method 5), but it is not able to provide weight-baring (evaluation method 6). In section 12.4, a conclusion is given in which remarks of experts are integrated (evaluation method 4).

methods and designs to be compared:

1) PTB-resins (standard PTB)2) PTB-ICRC3) PTB-Jaipur4) The Universal Below-knee Prosthesis5) ICEX-IDC6) ICEX-resins7) Hydro-cast/sand-cast

This six can be weighted against the criteria, of which some are further specified:

1) Universal 2 ) Comfort A)Socket fit B) Prosthesis weight C) Materials used and their effects (such as

perspiration).3) Easyfit A) Easy fit Amount of steps needed to fit and

produce a socket/prosthesis B) Specific knowledge needed4) Control5 Usable A) Donning/doffing and suspension B) Cleaning

12.1 scoring criTeria in comParison wiTh oTher ProsTheTic sysTems.

In section 10.4, Table 10-1, a rough com-parison between the Universal Prosthesis, the Ossur ICEX-system and a standard PTB-system was given.

However, the ICEX-system can be used with direct fabrication on the residual limb (the IDC-Icelandic Direct Casting system) and without direct fabrication (with plaster of Paris as shown in appendix N).

Both systems use the Ice-cast Compact pres-surizing device as shown in figure 4-7 and appendix N.

Also, the PTB is produced in two ways. The first is the vacuum technique with fibre rein-forced resins and the second is a polypro-pylene vacuum-forming technique. The latter fabrication method is used often in develop-ing countries, as a part of the ICRC (red-cross) design, by the aluminium/wood hand pro-duced Jaipur-system is very commonly used as well (see Wisse et al. 2002,2003 for more information about these production meth-ods). Water-cast/sand-cast prostheses are an important development, not to be neglected. This adds up to the following production

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6 Safe A) Design toughness B) Toxicity of the fitting materials and the

interface for user and environment7 Affordable A) Material/component price B) Service8) Cosmetics9) Quickfit10) Distribution

These are all compared with the commonly used PTB-resin system taken as a 100% refer-ence-index. The resulting table can be found in appendix Y, and a discussion per criterion below.

Note that the final verdict about for example affordability will be dependent on multiple points in the table (7,9 and 10) and the situ-ation that is reviewed (the market cycles as mentioned in section 6.3).

1) Universal

The Universal prosthesis offers a TCB-PTY-hybrid for amputees with a healthy residual limb, within a specified range of residual limb lengths, sizes and shapes. From data (appen-dix G) this range is expected to be P10-P90. For most of the amputees in this range it will provide a comfortable fit, however problems can be expected with amputees that:

- Have contractures (reduced knee movement) because of the reduced alignment possibilities of the prosthesis

- Have a bulbous residual limb shape.- Have a deviating bone structure (for example

as a result of bone fractures).- Have too little weight-bearing tolerance on the

interface with the frame (but just enough to allow total contact weight bearing).

For the latter, a prosthesis could be fitted without the user initially standing (with half of his body weight supported) in it fully. All these exceptions don’t add up to a group of more than 10% of all transtibial amputees, resulting in that the Universal Prosthesis is expected to be suitable for about 70-80% of all transtibial amputees that will ever find a comfortable socket.

Of course, this needs to be validated in prac-tise (see chapter 13).

The PTB-socket is, because all features are hand made from direct measurements, suit-able for all residual limb shapes, lengths and seizes, al long as they result in enough weight-bearing area’s (residual limb length is more than 80 mm). In practise, not all amputees fint the PTB-socket comfortable (because of pressure concentrations and fabrication mis-takes made by prosthetists). Probably around 90% of the fitted prosthesis will be experi-enced as comfortable.

The same reasoning goes for the TCB-socket, only with less influence of prosthetist-mis-takes and a suitability of around 95% can be assumed. The IDC-fabricated TCB-socket can not be fitted to bulbous residual limbs and will be confronted with roughly the same problematic residual limbs as the Universal Prosthesis.

The PTB-Jaipur system is made from drawing and measurements and doesn’t have a distal end pad. This results in higher pressures and will the system is comfortable for a smaller group than standard (70-80%).

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2 a) sockeT FiT

Socket comfort depends on the users expe-rience and therefore can not really be pre-dicted. Also, it has to be mentioned here that most literature (studies) in which prosthetics are functionally compared are with only a few subjects (n < 15) so significant data is limited. However, standard PTB-sockets are found to be satisfying in most cases (lets say 80%) and TCB-sockets even perform a bit better (85%).

The Universal Prosthesis will have a combi-nation of both, resulting in 85-90% comfort. However, because of less optimal use of pres-sure tolerant area’s and possibly a pressure differences during the TCB-fitting (pressuriz-ing the inner chamber of the prosthesis) as a result of the frames being in the wat, this percentage will drop to about 75-80%. Other systems compare, except the Jaipur which performs a little worse due to the lack of the distal end pad and due to the fabrication method. Again, 100% is taken as all amputees that can find a comfortable design.

2 b) weighT

The weight of the socket is highly depend-ent on the material used. This results in the following order from light to heavy: carbon-resins, glass-resins, either the Universal Prosthesis or the PP-ICRC-sockets and the most heavy being the Jaipur-socket.

The mass of the Universal Prosthesis frame is nearly nothing (<200 grams), but the socket will be filled with foam, increasing the weight. The foam itself is expected to weight up to 1 kg, but more heavy are the fibre-rein-forcements as proposed in section 11.2. Still, the total prosthesis (without foot) is expected to stay under 2 kg.

In the endoskeletal prostheses, where the pylon is separate from the socket, the pylon can be either heavy or expensive. This is important because weight more distally is experienced more cumbersome (and will take more energy during ambulation) that weight more proximal. The Jaipur and the Universal Prosthesis are the only exoskeletal systems in this comparison.

The Universal Prosthesis’s connector can be optimized by either taking by either taking redundant material away or examining the possibility to use other materials, resulting in about the same weight for all connectors used in the compared prostheses.

Conclusively, the weight-scores (compen-sated for the distal-weight) will all be close together.

2 c) maTerials Used and PersPiraTion

All sockets envelop the complete residual limb. Also in all cases, the prosthesis will be worn with socks or liners. The Universal Prosthesis might feel more hot, because of the isolating property of foam, however, after a few days of wearing a prosthesis (even in tropical countries) problems with perspira-tion usually disappear. The Jaipur might feel more foreign, because of the cold metal feel of the aluminium used.

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3 a) amoUnTs oF sTePs needed To FiT and ProdUce The ProsThesis

The Universal Prosthesis ant the ICEX-IDC are two systems in which the measurement/fitting and the fabrication method are inte-grated. Comparing appendix N and other sources on www.ossur.com with section 11.4, they both need about the same amount of steps to fabricate the sockets.

PTB-sockets have a separated fitting and fabrication method, which does increase the amount of steps needed. Because adjustments are might manually, the socket often has to be adjusted after fabrication. Even more so for the Jaipur socket, which is hand-made and adjusted many times, until a decent fit has been achieved.

3 b) sPeciFic knowledge needed

Specific knowledge is needed for all the sys-tems to be fitted.

For the Universal Prosthesis, this is basic knowledge, such as the preferred 5 degree flexion of the knee and the right foot posi-tions, can be communicated easily with manuals with figures or with easy-to-use measurement tools, such as the proposed fit-ting-foot-board (see chapter 10). All other sys-tems require advanced knowledge of biome-chanics and the residual limb anatomy. Even the pressure-cast/TCB-systems are produced after the prosthetist has applied pressure pads on the specific area’s of the residual limb that need to be shielded from the pres-sure. Additionally, the Universal Prosthesis and the IDC prosthesis do not require knowl-edge about the fabrication technique used, in contrast with the other systems.

4) sTiFFness

All current socket systems can be assumed to be almost equally stiff, because the socket designs are optimized that way. The resins will be slightly stiffer that the ICRC and the Jaupir, but not very significantly. The stiffness of the Universal Prosthesis is for the biggest part dependent of the function of the foam. The foam has not been developed yet, so the stiffness cannot be assessed. However, with the suggestion from section 11.3, a sufficient stiffness seems to be feasible. The Universal Prosthesis can always be made stiffer, by coating it with fibre reinforced resins, but at the cost of weight and size. Also, more straps can be added. Note that the strap at 100 mm below patellar tendon as shown in appendix R-12, cannot be found in the final design. It is expected to be unnecessary, until proven otherwise.

By mechanical principle, the exoskeletal designs are more stiff than the endoskel-etal designs. The Jaipur and the Universal Prosthesis score well here, but overall stiff-ness (control) is not expected to improve sig-nificantly by this.

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5 a) donning, doFFing and sUsPension

The donning/doffing-ease is dependent of the suspension type. In the comparison table, all possible suspension types of each system is shown. Except for the designs made for developing countries (ICRC, Jaipur), each can be fitted with all popular suspension systems. Beside this, no real differences for donning and doffing can be identified.

5 b) cleaning

All modular/endoskeletar systems can be more difficult to clean, because of the attach-ment points. However, most systems are finished with a cosmetic cover, eliminating problems. The Universal Prosthesis does not really provide a good protection for the tran-sition between the connector and the foot. Something that might prove easy to solve, either by adding a cosmetic cover for the complete prosthesis or the ankle piece only. The Jaipur-system consists of many material (finished with leather and paint) and is most difficult to clean.

6 b) ToxiciTy oF The FiTTing maTerials and The inTerFace For User and environmenT

Toxicity of the materials used is an impor-tant factor during use and during the fit-ting method, both in respect to the user/prosthetist as to the environment.

The used materials in all prosthetic compo-nents are generally non-toxic to humans.

However, glass-fibres, epoxy and especially polyester resins are difficult and dangerous to work with.

The heating and forming of the PP is not dangerous, when performed well.

Most methods (PTB,ICEX-resin, ICRC, hydro-cast) use plaster of Paris to cast and fabricate positive and negative moulds of the residual limb to form the socket around. The impact of plaster of Paris on the environment is low.

The Universal Prosthesis uses foam which is non-toxic. In addition, the prosthetist and the user cannot come into contact with it.

6 a) ToUghness

The frame parts of the Universal Prosthesis can easily be bended in transverse directions. However, Appendix S shows that they will not buckle. Performance will improve after the fitting procedure, because of the filling of the soft socket. Long term outcome (more than 2 years under dynamic loading) has to be assessed experimentally. All prostheses can be assumed to be safe. Some problems with ICRC prostheses have been observed when they where produced with recycled PP.

When the prostheses fail, their failure will probably be tearing of the material (espe-cially so with the exoskeletal systems), so that the user will have time to notice and does not fall.

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The Universal Prosthesis doesn’t produce much residual material and powder, except for the aerosol spray with probably some spare foam left in it.

When discarded (end-of-life of the prosthe-sis), the Universal Prosthesis is difficult to recycle. After fitting, the socket has become a mix of glass fibre, foam PP, aluminium, ABS and PU. Also the resins-based prostheses cannot be recycled. The Jaipur, made of basic material can be recycled best. The PP used in the ICRC-design can be recycled as well.

7 a) maTerial cosTs

Material prices are taken from 11.6, 3.3.1 and Wisse et al, 2004. They are summarized in the comparison table. For the comparison, the high (first-cycle) Universal Prosthesis price is taken, in which a budget for research is taken in account.

7b) service

Except for the ICEX (system from Össur) and the ICRC (from the International Committee of the Red Cross, factories in Switzerland and Ethiopia) the presented systems are widely available from a broad range of suppliers.

This implies that the prosthetist should deliver service and guarantees about the fit and comfort level. Knowledge about and experience with the fitting procedure is spread and varies in quality, but the amount of prosthetists that are known with the sys-tems is huge.

The Universal Prosthesis and the ICEX-sys-tems both have a centralized selling strategy, better enabling feedback and future develop-ments. Service in respect to material quality (for example wear resistance) can be consid-ered equal for all components, except for the Jaipur system, which is 100% dependent on the local workshop.

8) cosmeTics Cosmetics is most important during daily use (how does the finished product look), but also before and during the fitting procedure (trust of the user and the prosthetist in the system might depend on it).

Basically, all systems can be fitted with a (foam) aesthetic cover. Only the Jaipur system, though looks are acceptable because of the paint and because it is the only affordable system with a life-like foot under it, scores worst. It has a make-shift look.

The Universal Prosthesis is thicker than the average prosthesis, which might show, even when the prosthesis is worn under a pair of trousers. The frame does show that it has been thought about, tough that won’t be vis-ible anymore after fabrication.

9) qUick FiT

The time-consumption of the prosthetist and technicians is related to the amount of steps taken to produce the socket (see point 3). Times of standard PTB and ICEX-IDC are known from literature (see section 3.3). Estimations for other systems can be found in the comparison table. It has to be emphasized that all technicians and prosthetists have to be educated, except in case the Universal Prosthesis is used. This is also true for the Jaipur-socket. Its fit is highly dependent on the skill of the technician.

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10) disTribUTion

How well the system can be distributed is dependent of:

- the tools needed- the compatibility with currently used systems- services (see point 7B)- life-time/visits needed per year- and of course the dependency of the system

on the infrastructure (such as water, electric-ity, etc) and on the availability of prosthetists.

From the list, the tools and service types are specified in the table.

The life-time of all systems can be taken as 1 to 5 years (dependent on the activity of the user, with a mean of 2.5 years), which is com-parable to the use of a pair of shoes.

The current design for the Universal Prosthesis might have a shorter life-time, but a decent optimization and the right choice of foam will result in a lifetime in the same order.

All systems are well compatible with com-monly used connection systems (such as the pyramid connection core) except the ICEX-IDC (standard distributed with Össur com-ponents) and the Jaipur (though the used woodblock can be adapted at will by the tech-nician).

The Flexible sockeT:The frame parts can be adjusted by the prosthetist, either by plastic deformation of the hard frame parts) or by heating the inter-face frame parts. The small distal ends of the interface frame parts can easily be adjusted to provide extra weight-bearing, and no spe-cial knowledge is needed. However, changing the proximal end of the interface frame parts, needs experience and insight, and is not rec-ommended (nor necessary) for the un-expe-rienced. The flexibility is added to the design to facilitate the acceptance of the system by current prosthetists.

12.2 evalUaTion The concePT againsT The reqUiremenTs.

The requirements and design goals as pre-sented in chapter 7, are divided per cycle. During this project a concept was developed (chapter 11) that should comply with cycle 0. All requirements for cycle 1 and 2 where design goals, but not required as such. Also the requirements where catagorized by pros-thetic component or part. Hereafter follow remarks about the concept where necessary and which are not discussed in section 12.1 or where the Universal Prosthesis is expected to perform as well as a PTB-standard design.

The PosTerior side oF The soFT-sockeT:The prosthesis can be donned seated, cer-tainly when only reviewing the hard frame. It can be that the soft frame will be too long at the posterior side, because the fabrication liner can stay in between the brims (figure 12-1). In that case, some of the fitted and hard-ened prosthesis might need to be removed. Or an extra brim has to be developed that keeps the foam below while hardening and pressurizing. Figure12-1:A high posterior socket as a result

of the fitting of the soft socket. The brims will keep the fitting liner high (dotted lines).

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The advanced FiT sock:The fit sock can be further developed, so that it is thickened at places where the even-tual pressure will have to be lower than the pressure used during the foaming of the soft socket, especially the distal end. This will result in a bit more distance between the residual limb and the fabricated socket. After fabrication and without wearing the special sock, the pressure in those area will be lower than that used during the filling of the soft socket. This sock is comparable with the gel pads used during the fabrication of the ICEX-socket.

The mechanical ProPerTies oF The Pylon:It has to be mentioned here, that analysis of the mechanical properties of the pylon is incomplete. A working model has to be build and tested, to see if the pylon/socket combi-nation comes up to the requirements.

The whole design of the pylon might have to be rotated (about 5 degrees) to take the opti-mal 5 degrees of knee flexion in account. This is not so in the concept, the frame shapes have been derived from a stretched leg.

cycle 1 Prices:Tough the maximal total price for the system is correct and the concept does complies with it (see section 11.6), the maximal production costs of the parts is formulated completely wrong. For example, the socket mentions a total production cost price of maximal 500 USD. This has to be either the price inclusive R&D, or a percentage of the total production costs price. For example, the production cost price of the socket should not be higher than 80% of the production cost price of the total.

markeT share:For Cycle 1 a price was calculated with 1000 pieces sold a year for 5 year, resulting in an break-even price of 700 Euros. For Cycle 2 a break-even price of 200 was calculated with 10,000+1000 sold a year for 5 years.

These amounts of products sold are huge for the prosthetic market. For cycle 1 the market size

1.416.000 Amputees in Europe (see appendix F)X 54% which have a transtibial amputation (see

appendix F)X 70% that can be fitted with the UPis (see 12.1-

1)X 0.4 new prostheses needed a year for each

amputee (see 12.1-10)= 215.000 prostheses a year (total market size).

This is a market share of 0.47%, which is a lot considering:

- The current prosthetists have been using the current system for over 20 years.

- It will be difficult to reach all amputees in Europe.

- In Lower-income countries such as Rumania and Poland, the price of 700 Euro is high in comparison to the hour-price of technicians and prosthetists.

For cycle 2 the total market size adds up 2,300,000 pieces needed worldwide a year, with the same calculation:

This is a market share of 0.48%, which is a lot considering:

- The current prosthetists have been using the current system for over 20 years.

- Worldwide a lot of initiatives exist to promote the education of prosthetists.

- It will be impossible to reach all amputees.- The price of 200 Euro or even 100 Euros can

be considered high. Development of cheap systems that work on known systems (PTB-PP for example), with cheap components is being conducted and prices of other systems are expected to drop.

These market shares can only be reached within the 5 year periods when using exist-ing distribution channels, such as that of well-known companies or in this field operating NGO’s.

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12.3 model and FiT oF The Frame

shaPe

If we evaluate the shape of the interface frame, two things can be noticed. One, the model is slightly to big. This is an effect of the slices used of the Visual Human project. These were bigger than P95, probably because of conversion mistakes (see appen-dix R-10).

Secondly, the interface frame performs well in avoiding the pressure-sensitive areas and loading the pressure tolerant areas. The exception to this is the lateral place is the lat-eral edge of the lateral tibial condyle (figure 12-2). This load is the result of the need to connect the interface parts as defined in section 11.1.3. This place should be avoided better, possibly by increasing the distance between the interface frame and the residual limb.

Figure12-2:Assessing the fit of the interface frame parts.

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FlexibiliTy oF The weighT-bearing Frame

The model that has been build demonstrates that the first 200 mm from PT, the shape of the frame parts contributes to the strength and stiffness. Even when thermoformed, the frame parts do have enough flexibility to accommodate for a wide range of circumfer-ences at patellar tendon height, while staying in shape, so that the pressure-tolerant areas are loaded, and the pressure-intolerant areas are avoided.

However, the posterior weight-bearing frame is too flexible from 200 mm below PT and downwards. This can be solved, either by adjusting the material used, or by adding a rib. The anterior frame does perform well, as a result of the shape that it has to follow the tibial crest. Giving this shape to the two extensions of the posterior frame is another good option to improve weight-bearing per-formance. Additionally, a second connec-tor can be added, that can be used for long amputees at PT-260 mm.

Figure 12.3 gives an impression of the model.

Figure12-3:Impressionofthemodelbuild.

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12.4 ProjecT evalUaTion

bUilding From base

Looking back, it becomes clear that at the beginning of the whole trajectory toward the Universal Prosthesis (the design-for-all subject, the internship in Sri Lanka and the graduation project), all knowledge has been gathered from base.

Producing aluminium frame sockets in Sri Lanka, with anvil and hammer, was neces-sary to learn the properties of the materials and of the human body.

Being in Sri Lanka was necessary to learn what the wants and musts are of both prosthetists and users worldwide. In this project, the target was not to develop a cheap but inferior product for developing countries. Instead, the aim was to develop an excellent performing product for a good price that an be used worldwide.

Keeping the vision of the Universal Prosthesis clear and keeping trust in the intuitive notion that this vision is good, in spite of negative advices of some individu-als, was needed to keep going on until the needed technological innovations were con-ceived. Listening to other people is essential but never without listening to your own intui-tion.

The road To innovaTion

Around 1950 the quadrilateral AK-socket and the PTB-socket were developed (also see appendix E). These socket designs were two of the few fundamental innovations in prosthetics after WWII. It can be said that these and other important innovations are the work of a small group of people, one of them being J. Foort. In appendix X, the story of his experiences can be found. I found read-ing them really intriguing, because the devel-opment methods and processes he describes highly resemble the methods and processes of this graduation project. A few quotes to give an impression:

indePendency

This back-to-base strategy was needed to come up with a completely new system. In current day scientific research (also see sec-tion 13.1) the focus is too much on FEM-anal-yses and modelling and functional outcome analyses between PTB and TCB-sockets. This also explains why this project was done by an industrial design engineer, and not by a team of prosthetists. Prosthetists know too much to even think about making a low-expert system.

Now the most innovative steps have been taken, and the system needs to be optimized, bringing a team together of prosthetists, engi-neers, market experts, etc is the only way to ensure a practical and high-quality product.

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13recommandation

In the evaluation it has become clear, that the concept presented in this report needs to be further improved (better properties) and further developed (made market ready). In section 13.1 recommendations for fundamen-tal research that needs to be conducted can be found. Section 13.2 offers specific sugges-tions for improvements of the universal pros-thesis.

Section 13.3 discusses possibilities on how to continue the development of the universal prosthesis.

13.1 FUndamenTal research in ProsTheTics.

All interface design starts with knowledge about human behaviour and the human body and its properties. Prosthetists make prod-ucts for people. The prosthesis replaces a (lost) body part and restores a function that is lost and is needed for the participation of the user in society. Logical, it seems.

The lack oF knowledge aboUT shaPe and ProPerTy variances

For the development of the Universal Prosthesis, the data that was gathered in Sri Lanka (appendix G) was of utmost impor-tance. It was assumed that the bone-structure for everybody is the same and only propor-tions (scale) differ. This assumption has to be validated.

This can be achieved by scanning the limbs of a range of people (N>100). Scans can be made with CT or MRI. Other (less preferred) approaches are the study of corpses and the study of 2D-X-ray images. These people don’t have to be amputees, though this would improve the data.

Better insight in the variance of the bony structure and the soft tissues of people leads to a better optimized interface frame fit, and a better overview of the group for who the Universal Prosthesis would provide a com-fortable solution.

The lack oF knowledge aboUT PressUre Tolerances Now, the amazing part of the story is that fundamental knowledge about the anatomy and properties of the human body (needed to design an interface) in literature is either extremely out-dated and lacking or not public available. Ming Zhang concludes in his overview of FEM-analyses [Zhang 1998], that mechanical properties of the soft tis-sues are little known. A bigger question is the tolerance to load of the tissue. Zheng in “state-of-the-art methods for geometric and biomechanical assessments of residual limbs: A review” states: “While FE analysis can estimate the stress distribution within the residual limb and the socket interface, it cannot tell us whether a stress distribution is good or not. A good interface stress distribu-tion should facilitate effective load transfers during gait and should be well tolerated by the residuum soft tissues. Such tissue toler-ance involves tissue damage criteria and tissue adaptation mechanism in response to external loading. How residuum tissues react and adapt to external loading deserve much further investigation.“ While FEM-analyses are numerous, nobody actually knows what pressure distribution they are looking for.

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The PTb-Tcb baTTle

This lack of knowledge about whether a pres-sure distribution is good or not results in a battle between promoters of the PTB and promoters of the TCB-system. Comparative studies are being conducted but with a small population in subject groups.

Worse, the studies that are conducted are functional outcome studies in which both sockets are fabricated for the same subject (in which a slight, but often insignificant preference for the TCB-sockets can be seen). However, the PTB-socket is a hands-on socket design, which means that the experience and the knowledge of the prosthetist are the determining factor. The prosthetist will make

“mistakes” which results in a negative outcome bias for the PTB-socket . The TCB-socket on the other hand is a hands-off socket design. There is less chance that the fit will not be optimal after the fitting procedure.

These two factors should be split and studied separately:

- A study determining the functional outcome differences between hands-off and hands-on systems.

- A study determining the functional outcome between rectified and unrectified systems (such as the PTB and the TCB sockets).

Before the development of the Universal Prosthesis this could be achieved by:

- Comparing hands-on and hands-off produced TCB’s.

- Comparing hands-on produced PTB’s with hands-on produced TCB’s.

Now, because the Universal Prosthesis is a hands-off produced PTB also it can also be compared with hands-off produced TCB’s. None of the mentioned comparisons have been made in literature.

13.2 imProving The Universal ProsThesis

The Frame

When more data about the variance in residual limb shapes and tissue structures and more data about the pressure tolerance of residual limb tissue is obtained, the frame shapes can be optimized in respect to anat-omy.

FEM-analyses can be a valuable tool for the optimization in mechanical properties. Ribs on the frame parts, especially the injection moulded interface frame parts, can improve their properties significantly. It might be nec-essary to add more connective belts between the weight-bearing frame parts.

Other materials might prove more suitable for the frame. For example, Hylite could also be used for the interface frame, while glare or possibly normal aluminium could improve the performance of the weight-bearing frame parts.

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Improvements would include:

- a better, more comfortable fit- a wider group that can be fitted with the

Universal Prosthesis (bigger target group)- a lighter prosthesis- a stiffer prosthesis (more control)

The soFT sockeT

Absolute priority is the development and testing of the foam that will fill the prosthe-sis. Without a proper foam, the complete con-cept fails. The posterior side of the prosthesis might prove to be in the way for donning/doffing and sitting as shown in figure 12-1.

cosmeTics

Cosmetics after fabrication of the Universal Prosthesis can and needs to be further improved. A prosthetic cover can be put over the outside, but it can also be put inside the prosthesis. In that case the fitting liner is pulled over the frame and the cosmetic socket. Another option is to integrate it in the frame (as was the intention). Now, the problematic shape difference between the Universal Prosthesis and a natural leg occurs near the connector, where the frame is too triangular.

cosT redUcTion

To make the Universal Prosthesis a real suc-cess in cycle 2, it have to overcome the high competition during cycle 1 (section 6.3). A lower price would give the system the edge over the ICEX-system it needs. Costs can be reduced by smart use of subsidies and grants. Also, this project might best be developed in universities. In that case, initial investments needed for R&D are lower, but the problem might be that no companies are willing to take the risks that come with production, because the design is not patented or pro-tected otherwise, as discussed in the next section.

13.3 ProjecT conTinUaTion

There are basically three realistic options to continue this project:

1) Find an enthusiastic entrepreneur, that is willing to start a company, bring together several business-partners, such as a orthopae-dic workshop, a hospital, a knowledge insti-tute (university) and try to start independent production of the Universal Prosthesis. The success of this enterprise would be highly dependent on the amount of subsidies and grants that can be attracted.

2) Find a big player in the current market, such as Otto-Bock or Össur, and start in-house development of the Universal Prosthesis as a new addition to their assortment.

3) Try to encourage America/Canadian research institutes, such as the US National Rehabilitation Information Center, to take up the project and develop it further with help of the world-wide prosthetic scientific research community.

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Option two is preferred, because in this way quality and development speed of the Universal Prosthesis can be controlled. Also, when production is started, a company will benefit most by wide-spread use of the system and will actively promote it. Contact has been sought with Össur to discuss this possibility. However, to make commercial exploitation feasible on a broad scale, protec-tion of the intellectual property is a must. A patent is a way to protect the knowledge. It has to be emphasized that the development of the Universal Prosthesis will cost consid-erately and that the investments for this R&D will have to return to the entrepreneur to ensure future developments and continues production.

It might well be that the time just is not ripe for the Universal Prosthesis to appear on the market. Tough the tendency (trend) of the branch towards standardized systems, with customized results has been identified, prosthetists still keep using their well known systems, such as the PTB-resin system. And why not, it does perform well, and the needed knowledge to fabricate them has been invested in (years of training by exactly those prosthetists). The negative attitude towards the new systems by some (and the naïve positive attitude to new technologies by others) can even be read between the lines in literature publications. It takes time for the prosthetists to realize that with the Universal Prosthesis (and other low-expertise systems) their knowledge doesn’t become obsolete, but that it can be used better and with more effect elsewhere.

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14concLusion

“I urge you to do this – aim for universal solu-tions “ J. Foort, Appendix X.

Is the development, production and distribu-tion of an Universal Below-Knee Prosthesis feasible?

Yes it is.

But the road is long.

qUick: The Universal Prosthesis can be fitted within an hour. The efficient use of the prosthetist’s time, can lead to cost reduction and better overall healthcare in current orthopaedic workshops. Patients for which a prosthesis is now regarded as too expensive or time-con-suming (for example bed-staying elder, with a bad prognosis), can be fitted more easily. Also, the amputee can be a prosthesis more often, for example during the post-operative period (1-6 months after amputation) or as a spare one when the custom-made prosthesis is being repaired or being replaced.

low-exPerTise: The Universal Prosthesis can be fitted by relatively un-educated people. This unique features addresses the lack of experienced prosthetists worldwide. The educated prosthetists can use their valuable time to solve orthopaedic problems for people with non-standard BK-amputations. In the long run, more people can benefit from proper prosthetic care.

14.1 sTrengThs

The Universal Prosthesis has some unique features or Unique Selling Points (UPS). Its strongest point is that the Universal Below-Knee Prosthesis combines a customized, com-fortable fit with a low-expertise fitting proce-dure. This strength fits in the market trend toward standardized systems that provide a customized fit.

comForT: The Universal Prosthesis combines the Total Contact Bearing (TCB) and the Patellar Tendon Bearing (PTB) weight-bearing prin-ciples. During the fitting procedure, the amount of pressure added during the filling of the soft socket, will determine if the pros-thesis will behave more like a TCB or more as a PTB socket. This flexible system ensures that a wide range of amputees can be fitted with a comfortable prosthesis.

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14.2 ProjecT Progression

The here-presented concept if far from fin-ished. A lot of fundamental questions have to be researched to improve the base of knowl-edge on which this innovation is build. Apart from that, the frame parts have to be opti-mized and the formation of the soft-frame, by filling the prosthesis with foam, has to be developed from scratch. When the first series of prostheses become available clinical/field test have to make sure the procedure is indeed understandable and efficient when performed by non-experts. After that, bring-ing it to other markets, other cultures and other environments brings along a complete new set of challenges.

commercial FeasibiliTy

It is clear that a huge amount of research and development work has to be done before the Universal Prosthesis can be a qualita-tive system, that has an edge over other cur-rent prosthetic systems. And R&D-work is an expensive investment that needs to be returned by the revenues of the product.

With 2 x 800.000 Euros R&D-investments, the Universal Prosthesis can be developed. Return of investment is possible when sell-ing 1000 Universal Prostheses for 5 years at a price of 700 Euros and then selling 11,000 pieces a year for 5 more years at a price of 100-200 Euros. These market share of 0.47% will be difficult to reach. Strategies to do so include:

- Cutting down on R&D-costs by attracting grants and encouraging many parties to par-ticipate.

- Get support from existing distribution net-works, including NGO’s, producers of pros-thetic components and governments.

- Integrate the Universal Prosthesis into an assortment of prosthetic systems, components and methods, so that the R&D costs can be spread over a group of products.

14.3 Final word

History learns us that innovation in socket designs doesn’t occur often. However, innova-tions that occurred, such as the PTB-socket and the quadrilateral socket, did become mainstream. These innovations were not pat-ented, were not commercialized, but were developed by a relatively small group of enthusiastic scientists and practitioners.

Because the Universal Prosthesis is a prod-uct that will only be economically feasible when produced in large quantities, for this new innovation commercial exploitation might be the best option.

I know that the development of the Universal Prosthesis is not finished. But I feel that the here presented concept is a good step towards the next generation of prostheses. Whether the concept is freely developed or com-mercialized, I believe that within 10 years, many people can benefit from the Universal Prosthesis or similar innovations. And I hope that some of the 1,000,000 people that cur-rently are without proper prosthetic care, will be able to walk once more.

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- Wisse BM, WD van Dorsser, F Soleymani, ProsthesisforSriLanka–Prosthesisfortibialamputeesfocusedonthe3rdWorld, Delft, 2002

- Wisse BM, WD van Dorsser, TheAlternativeProsthesis–finalreportinternshipSriLanka2002, Delft, 2003

- Seymour R, ProstheticsandOrthotics:lowerlimbandspinal, USA: Lippincott Williams & Wilkins, 2002

- IMT-Baghdad, Institute of medical technology department of rehabili-tation, Baghdad, Iraq, Educationfororthopedictechnician,Part1–Symesandpartialfootprosthesesandbelowkneeprostheses, year unknown

- CBS, Centraal Bureau voor de statistiek, StatistischBulletin, 60e jaar-gang no. 5 / 3 februari 2005

- CBS, Centraal Bureau voor de statistiek, Statlineonlinedatabase (web-site): statline.cbs.nl, 2005

- IEE, MedicalEquipmentIndustry-potentialforgrowth, edited by pro-fessor Alan Murray (Freeman Hospital), 1998

- VHI, Veteran Health Institute, TraumaticAmputationAndProsthetics, Independent Study Course, May 2002

- Weeks DL, PreliminaryInvestigationComparingRectifiedandUnrectifiedSocketsforTranstibialAmputees, Journal of Prosthetics and Orthotics 2003; Vol 15, Num 4, p119

- Fisher SV, G Gullickson Jr., Energycostofambulationinhealthanddisability:aliteraturereview, Archives of Physical and Medical Rehabilitation. 1978 Mar; 59: 124-133.

- Angarami GR, AnEfficientLowCostProstheticStructuralSystem, Journal of Prosthetics and Orthotics 1989; Vol 1, Num 2, p86.

- Valenti TJ, ExperiencewithEndoflex:AMonolithicThermoplasticProsthesisforBelow-KneeAmputees, Journal of Prosthetics and Orthotics 1991, Vol 3, Num 1, p43.

- Schoppen T,Physical,MentalandSocialpredictorsoffunctionalout-come, Rijks Universiteit Groningen 2001

- ACA, Amputee Coalition of America, FirstStep2001, www.amputee-coali-tion.org/aca_first_step.html.

- Kriesels M, ProthesesvoorSriLankauitfietsonderdelen, 2002, please contact the writers for more information

- UK NHS, 2005 (website): www.pasa.doh.gov.uk/prosthetics/- Walsh TL, CustomRemovableImmediatePostoperativeProstheses,

Journal of Prosthetics and Orthotics 2003; Vol 15, Num 4, p158-161.- COTA, Centrum voor Orthopedie Techniek Amsterdam, DeSoftsocket,

2002- Hafner BJ, JE Sanders, JM Czerniecki, J Fergason, Transtibial energy-

storage-and-return prosthetic devices: Areviewofenergyconceptsandaproposednomenclature,Journal of Rehabilitation Research and Development 2002; Vol 39, Num 1, p1-11.

- Michael JW, JH Bowker, Prosthetics/OrtheticsResearchfortheTwenty-firstCentury:Summary 1992 Conference Proceedings, Journal of Prosthetics and Orthotics 1994; Vol 6, Num 4, p100.

- Sangeorzan BJ, Harrington RM, Wyss CR, Czerneicki JM, Matsen FA, CircularyandMechanicalResponseofSkintoLaoding,Journal of Orthopaedic Research 1989, Vol 7, p425-431

- Foort J, 1986, Innovationinprostheticsandorthotics,TheKnudJansenLecture, Copenhagen 1986

- Kim WD, Lim D, Hong KS,Anevaluationoftheeffectivenessofthepatellartendonbarinthetrans-tibialpatellar-tendon-bearingprosthesissocket, Prosthetics and Orthotics International 2003, Vol 27, p23-35

- Reswick JB, Rogers JE, ExperienceatRanchoLosAmigoshospitalwithdevicesandtechniquestopreventpressuresores, Bedsore Biomechanics, 1975

- Convery P, Buis AWP, Socket/stumpinterfacedynamicpressuredistributionsrecordedduringtheprostheticstancephaseofgaitofatrans-tibialamputeewearingahydrocastsocket, Prosthetics and Orthotics International, 1999, Vol 23, p107-112

- Zhang M, Mak AFT, Roberts VC, Finiteelementofaresiduallower-limbinaprostheticsocket:asurveyofthedevelopmentinthefirstdecade, Medical Engineering & Physics 1998, Vol 20, p360-373

- Datta D, Harris I, Heller B, Howitt J, Martin R, Gait,costandtimeimplicationsforchangingfromPTBtoICEXsockets, Prosthetics and Orthotics International 2004, Vol 28, p115-120.

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F FigUres & TablesList

Tablesandfigures

Table2-1: Project targets before and after the Sri Lanka internship [Adjusted from Wisse et al. 2003, Chapter 5] (For a complete timeline see appendix C). 2

Figure3-1: The prosthesis and its total context. 6Figure3-2: Bones of the lower limb (most right), muscles (middle) and

anatomy of the residual limb (below) [Adapted from IMT-Baghdad and Wisse et al. 2002]. 7

Figure3-3: Amputation procedure [Seymour 2002]. 8Figure3-4: Different levels of transtibial amputation [Seymour 2002].8Table3-1: Amount of amputees worldwide. 9Figure3-5: Residual limb shapes: conical (a), cylindrical (b) and bulbous

(c). [Seymour 2002] 10Table3-2: Skin conditions. 11Figure3-6: Pressure tolerant and sensitive areas. Most left: A scematic

of sensitive (light red) and tolerant (dark red) areas [Seymour 2002]. 4 Right: anterior, lateral, anterior and medial view of a positive (cast), with pressure sensitive (red) and to 12

Figure3-7: Base of support. The size of the base of support varies with a change in foot position. [Seymour 2002] 13

Figure3-8: Static alignment for a transtibial prosthesis. A) In the fron-tal plane, B) In the sagittal plane. [Seymour 2002] 13

Figure3-9: Inclination of the bulge of the PTB (see section 4.2) socket. The bulge provides more surface for weight bearing than the wall of the socket. Note the relatively longer horizontal component of the vector. [Seymour 2002] 14

Figure3-10: Forces on the patellar tendon increase because of the need to compensate moments due to distance a and b and because the inclination of the force factor on the patellar tendon [Wisse et al .2002] 14

Figure3-11: Alignment of the transtibial prosthesis in the sagittal plane, placing the foot medial to the socket. This placement tends to cause a rotation of the socket that then places pressure on the proximal medial and distal lateral residual limb. 15

Figure3-12: Alignment in the sagittal plane placing the foot lateral to the socket, resulting in pressure on the fibular head and distal medial residual limb. [Seymour 2002] 15

Figure3-13: Alignment in the frontal plane. Left: normal. Right: Foot placed to far backward, causing pressure on the distal ante-rior part and proximal posterior part of the limb. 15

Figure3-14: Alignment in the frontal plane. Left: normal. Right: Foot placed to far forward. If the force though the spocket fell posterior to the ground reaction force vector, the prosthesis would tend to rotate. 15

Figure3-15: Planes of the body. [Seymour 2002] 16Table3-3. Phases in gait. [Seymour 2002] 16Figure3-16: Distance variables of giat. a) left step length, b) left stride

length, c) right stride length, d)right step length, e) width of base support f) Right toe-out, g) left toe-out [Seymour 2002] 16

Table3-4: Phases of the gait cycle of the right leg. [Adjusted from Seymour 2002]

Figure3-17: Gait deviations to accommodate a long limb. A) Hip hiking, B) Lateral trunk lean, C) Circumduction, D) Vaulting, E) Excessive hip and knee flexion. [Seymour 2002] 18

Figure3-18: Procedures of a prostetic clinic [Adapted from Seymour 2002] 21

Table3-5: Grow indexes of the sales in the medical equipment indus-try in the Netherlands [CBS 2005]. 22

Table3-6: Market for prostheitc devices in the Netherlands [CBS 2005]. 22

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Table4-1: An overview of clinical patient stage and applicable prosthe-sis type. In practise, the choice is less time dependent, but is determined by the healing rate and activity level of the amputee. 24

Figure4-1: Fabrication of a RRD and Custom Removable IPOP. Left: 3 spandex socks, pads and an attachment plate, 3 velcro straps and attachment base plates. Middle: fiberglass cast with cut lines and base plate attachment points and the result. Inset: ant 25

Figure4-2: A complete IPOP (without pylon). [Source: Seattle Rehab Research, US Veteran Affairs] 26

Figure4-3: The universal IPOP (Aircast Air-limb) is inflatable to acco-modate different stump sizes. [source: ACA 2001, Aircast brochures] 26

Figure4-4: The Flow-tech Adjustable Postoperative Protective and Preparatory System (APPOPS) provides a prefabricated prosthetic system offering protection, controlled shaping of the residuum and early rehabilitation.... 27

Figure4-5: Connective part between socket and pylon, which can be used in temporary and definite prostheses. [Source: Endolite brochure] 28

Figure4-6: Components of Maramed orhopedic Systems. Left: X-tender system can be used as a temporary prosthesis(middle). At the right a retainer is shown, in which a custum-made socket can be attached. [Source: Maramed website] 28

Figure4-7: The ICEX toolbox and component box. [Source: Ossur web-site] 29

Figure4-8: Standard fabrication starts with taking a negative mold. Then plaster is poured into the negative mold to create a positive mold. At last, the positive mold is shaped by the prosthetist to emphasis the shape. The final socket is made by laminat 29

Figure4-9: The exoskeletal prosthesis (depicting socket, plastic exterior and foot) is one, integrated product. [Seymour 2002] 30

Figure4-10: The Jaipur prosthesis, here drying from paint finish, consists of a exoskeletal structure with a separate manufactured foot. [Source: FINS- Sri Lanka] 30

Figure4-11: The endoskeletal prosthesis always contains a pylon. Very seldom the other parts are integrated. Normally, the socket and foot are modular components. [Seymour 2002] 31

Figure4-12: The 4C Air Lite Monolithic (above 2 pictures show manu-facturing steps. A carbon-fibre sock is one of the important materials) and the Endoflex (lower pictures) are two of the few designs in which the pylon and socket are integrated. [4C Air-Li 31

Figure4-13: ISNY Components [Source: Website Otto-Bock] 32Figure4-14: Flexible ischial-containment socket for transfemoral

amputees (this one from Otto-Bock, inset from Hanger) con-sist of a flexible inside and a frame. Other names include Total Flexible Brim, the ISNY and SFS (Scandinavian Flexible Socket)[Seym 33

Figure4-15: Plug fit socket. The first prosthetic socket without weight-bearing at the distal end by Verduin 1696 [Wetz 2000] 34

Figure4-16: Icex finished socket (left). Pressure pads are added to com-pensate for weight intolerant areas (cutt-through right) [Source: Ossur Icex brochures.] 35

Figure4-17: The ICRC-limb makes use of a polypropylene pylon.. Its cross-section is H-shaped. 35

Figure4-18: (left) Trimodular Pylon as used in the sauer-bruck trimodu-lar physiological prosthesis [Angarami 1989] 35

Figure4-19: (right) Springlite Advantage DP flexible pylon and dynamic response foot by Hanger Orthopedic Group. [Source: web-site] 35

Figure4-20: Left: Principle of Rocker foot or sole. [Adapted from: www.customfootware.com] Right: Low cost prosthesis with cane pylon and rocker foot 36

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Figure4-21: SACH foot (Adapted from Seymour 2002] 36Figure4-22: SAFE II foot. (Original manufacturer is Campbell Childs Inc,

now bought by 4C (Foresee Orthopeadic Products)). 36Figure4-23: Single-axis foot. [Seymour 2002] 37Figure4-24: Multiple axis foot. [Seymour 2002] 37Figure4-25: STEN foot. [Source: Kinsley Manufacturing Co brochure] 37Figure4-26: (Above) Though from the outside not visible, energy storing

feet differ from the inside [Impulse foot, OHIO Willow Wood] Various energy-storing feet. Earch foot is composed of a com-pressible heel and a flexible keel spring. A) Seattle foot, B) Dynamic foot,C) STEN foot, D) SAFE foot,E) Carbon Copy II foot.[Hafner et al. 2002] 38

Figure4-27: Advanced energy-storing prostheses: A) Modular III, B) Reflex VSP, C) Advanced DP, D) Pathfinder.[Hafner et al. 2002] 38

Figure4-28: Two hybrids: The Seattle Cadence HP [Source: Seattle web-site] and the MICA Genisis II+. [Source: MICA website] 38

Figure4-29: (right) Anatomical Suspension. The supracondylar suspen-sion is in this case removable due to the brim.(right, middle) The supracondylar suprapattelar system is fixed. [Seymour 2002] 39

Figure4-30: The PTB cuff or supracondylar cuff. [Seymour 2002] 40Figure4-31: The thigh corset can be used in conjuncture with a waist belt

and an elastic strap. [Seymour 2002]. The suspension sleeve has a similar working principle (left) [Otto Bock]. 40

Figure4-32: Pin/Shuttle suspension. [Seymour 2002] 41Figure4-33: Mineral gel sleeve suction suspension. [www.customprosthet-

ics.com]. 41Figure4-34: Double/Single Socket Gel Liner [Silipos]. 42Figure4-35: Demountable Torque absorber and its effects. [adapted from

endolite] 42Figure4-36: Some examples of connective components [adapted from

www.atlas-ti.com] 42

Figure4-37: Prosthetic skins can have a high life-like appearance [left, dorset and orthopeadic]. Uflate sleeve skin covers shrinks to fit the prosthesis when treated with a heat-gun. 43

Figure4-38: Examples of supplies (above): Rivits, Polyester Resin-Laminae, box of stockinettes, pneumatic cast cutter, carbon tape [Fillauer Supplies brochure]. Static alignment is done on an alignment table [otto bock[. Supplies enable prosthetists to ma 43

Figure4-39: Pathway of the instant axis of rotation for the knee joint. [Seymour 2002] 44

Figure4-40: Limited dorsiflexion at the ankle. If the ankle can not dor-siflex normally, either A) the individual will weight bear on the toe or B) the knee must hyperextend to get the foot flat on the ground. [Seymour 2002] 44

Figure4-41: Stress on the residual limb from the prosthesis. A) The hypothetical situation in which the residual limb is of uni-form firmness and the socket matches the circular shape of the limb. B) A residual limb of nonuniform firmness and a socket that 45

Table4-2: Gait deviations due to materials and the alignment [Seymour 2002]. Note that many alignment choices can have the same effect. If the effect is unwanted, all can be adjusted, but some will cause other problems (because one alignment choice will h 46

Figure4-42: Bending forces on the residual limb while standing. [Wisse et al. 2002] 47

Figure4-43: A Simple model of the value chain of prostheses. Value is increased from left to right. Note that some companies have multiple roles. 48

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Figure5-1: Figure-8 wrap for the transtibial amputation: [Seymour 2002] A. First wrap max extend from proximal medial to distal lateral. B. Second wrap may extend from proximal lat-eral to distal medial. C. Thrid wrap may overlie first wrap. D. Bandage is looslely wrapped approximately 60 milimeter to the knee. E. Completed wrap. 51

Figure5-2: LEFT: The endolite Aqualimb with anto-slip tread patterm on the sole for extra grip on wet surfaces. [www.endolite.com]. RIGHT: The rampro activankle swimming prosthesis [www.rampro.net]. 55

Figure6-1: Snapshots of a movie, in which an amputee walks several steps in a frame socket. [Wisse et al. 2002] 61

Table6-1: Several fitting methods and their properties. 64Table6-2: Several walking and mobility aids and their properties 65Figure10-1: Otto-Bock Harmony system 82Figure10-2: Possibilities for adding use-cues to ease the fitting proce-

dure. 83Figure10-3: Moments around the socket, as a result of diffrent pylon

types. 85Figure10-4: H-profile. 85Figure10-5: Flexible bands that connect parts will result in pressure

peaks. 85Figure10-6: Suspension sleeve 86Figure10-7: Steps for fitting the hard frame 88Figure10-8: Steps for fitting the soft frame 88Figure10-9: Steps for fitting the combined system 89Table10-1: Quick comparison between the Universal Prosthesis and two

popular fitting systems.e 90Figure11-1: 13 stacked layers that where derived from the anatomy of the

residual limb. Top view and isometric view. 94Figure11-2: Together with the resulting frame parts. [Top] stiff frame,

two views. [Below] interface frame. 94

Table11-1: Four material options for the interface frame. 95Figure11-3: Applying hinges to Hylite (source: Corus) 96Figure11-4: Deep drawed car part from Hylite. (source: Corus) 96Figure11-5: Less space in between the frames is better; it results in a

stiffer prosthesis. 99Figure11-6: A Polyurethane layer is partly reinforced with fibres. The

Hylite is milled to better attach the reinforced PU. The two Polyurethane layers can slide along each other 99

Figure11-7: The airman Panter is an example of a hand-pump. 100Figure11-8: Two ways to connect the frame. 100Figure11-9: An extra component that can fine-tune the length enhances

the adjustability of the prosthesis. 101Figure11-10: The connection to the foot is 101Figure11-11: (Up and Right)The airlock is achieved by an outer and an

inner seal. 101Figure11-12: The fill channel and the valve in the connector. To transfer

the filler up to the proximal side of the prosthesis, flexible tubes (straws) and splitters can be used. The entrance of the channel has to be distally or on the bottom of the ...102

Figure11-13: An example of a Minivalve (source: www.minivalve.com)102

Figure11-14: Height of supracondylar suspension. 104Figure11-15: The shuttle for the pin/shuttle suspension can perforate the

outer layer. The rings will restore the system to an airtight state. The shuttle can be attached on most heights (with varying circumference). During the fitting .... 105

Figure12-1: A high posterior socket as a result of the fitting of the soft socket.

Figure12-2: Assessing the fit of the interface frame parts.Figure12-3: Impression of the model build.

the universal prosthesis -- report 2005-11-18

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