prosthesis

PROSTHESISPresented by

Dr. Chiranjeevi.JMPT Neuro, FNR

Prosthesis

Prosthetics deals with the prescription, design, fabrication & fitment of artificial limbs in a scientific manner. Any artificial substitute which is meant to replace the lost part of the body is called prosthesis.

These may be internal or external. External prosthesis are artificial lower & upper limbs,

dentures & artificial eye. Internal prosthesis is replacement prosthesis for

joints & heart valves

Prosthesis is given in cases of amputation. After amputation these devices are used to replace the missing part.

Before fitting the prosthesis we have to assess the stump. Cause of the amputation Associated diseases Skin- ulcer Scar (adherent, healed) Sensation (absent, diminished, hyper aesthesia)

Circumference bulk, wasting, edema. Shape (conical, quadrilateral) Temperature Pain (type, location, duration) ROM of residual limb (remaining joints) &

other extremity (major joints) Muscle strength of major residual muscles

groups, other extremities.

Classification of lower limb amputation:

Due to medical considerations the part of the limb or the whole limb is amputated.

The classification of classical lower limb amputations is: hemipelvectomy (hind quarter amputation) Hip disarticulation. Above knee amputation. Below knee amputation. Simi’s amputation. (ankle level) Choparts amputation. (mid tarsal level) Lisfranc’s amputation. (tarso metatarsal level) Disarticulation of toes.

BIO engineering principles in the fitting of artificial limbs for Amputees

The application of bio engineering principles for the study of ambulation and limb fitting techniques are

Modern surgical procedures in amputation Shape of Socket of artificial limbs Alignment studies of Artificial limbs

Modern Surgical Procedures in Amputation

The criteria for selecting the level of amputation of a limb are the extent of the disease or trauma and the status of the vascularity.

But the consideration has to be given for Length of the Stump Longer the stump, better in the leverage. It is easier

to stabilize an artificial limb with a longer stump than with a short one. Hence, the surgeon aims for the longest possible stump preserving as much vital tissue as possible instead of selecting sites of election for amputation

Preservation of Functioning Joints: It is necessary to preserve the joint as much

as possible. No mechanical joint can replace human joint in efficiency , control, stability, wear and tear to an equal extent. Loss of joints results in instability due to the changes in the line of weight bearing and centre of gravity.

Preservation of stump musculature: For effective manipulation of an artificial limb,

it is necessary to have a good stump musculature and good power. This is often achieved by special surgical techniques, such as suturing the muscles in an orderly way and fixing the muscles at the cut end of the bone which is called as the “myodesis” technique. It is made more powerful with a good post-operative physiotherapy. Such as stump has maximum dynamic power to operate an artificial limb.

Shape of socket of artificial limbs: For achieving maximum comfort and good

stability of the amputee with an artificial limb. The shape of the socket should be:– confirm to the shape and counter of the stump.– Accommodate the differences in relative firmness

of the tissues of the stump.– Accommodate for different tolerance to pressure.– Have a relative inclination of supportive surface.

Alignment studies of artificial limbs: Alignment refers to the relative position of the

various parts of the prosthesis with respect to each other. The alignment influences the magnitude and distribution of forces applied to the stump by the socket. Unless the alignment is perfect, the patient cannot walk with a normal gait.

Alignment has to be checked and adjusted in two planes.

1.medio-lateral alignment 2. Anterior posterior alignment

This is carried out by inserting an alignment device below the socket. By making the amputee walk with the trial limb alignment device in various positions and maximum comfortable position in determined.

During the final check out of the prosthesis the alignment is rechecked. The position of the pelvic band, the position of the joints and the line of weight bearing are verified to see that they confirm to the normal anatomical relationship.

Stump exercises

Exercises for the stump are started even from the third day after amputation. They are very essential as they prevent many of the complications during the post operative period.

Free exercises are advocated which helps in wound healing by improving activity and circulation.

In case of bilateral amputee, hydrotherapy is of great valve. Bilateral lower limb amputees should develop the upper limb muscles well.

Unilateral lower limb amputees have to develop the normal limb also.

Isometric exercises for: Quadriceps in below knee amputations: Hip extensors & adductors in high AK Amp. Hip extensors & abductors in low AK Amp. Upper limb amputees are given intensive physiotherapy to

improve the muscle power in the elevators, depressors, protractors, retractors of the shoulders. Because these groups help the functioning of prosthesis.

Advantages of stump exercises:

Increases the circulation in the stump & aids wound healing.

Promotes the venous drainage & prevents edema of the stump.

Prevents the development of stump deformity. Prevents joint stiffness. Keeps up & promotes the muscle power of the

stump. Prevents the phantom limb pain or phantom pain

sensation.

Classification of prosthesis.

Prosthetic construction design is of: exoskeletal. endoskeletal.

Exoskeletal Prosthesis: Gains structural integrity from the outer laminated

shell. Usually made of resin. Which is quite durable, over a filler material of wood or foam, which has been shaped to provide cosmetic appearance of prosthesis?

Endoskeletal prosthesis: This is more modern in design. This was light

internal modular components & tubing to provide strength & weight bearing capabilities.

It gains its structural integrity from the inner endoskeleton-a pylon made of metal or carbon fiber

Materials used: Wood - Has several advantages; it is light weight, strong &

easy to work on. Leather – is soft, natural & biocompatible. It is however

expensive. Cloth - keeps skin dry, and acts as a cushion for the limb, by

absorbing shear forces. Plastics – increase strength & elasticity, but are unfortunately

not biocompatible. Many like polypropylene & polyethylene are durable, cheap and easy to mould.

Fiber glass- which is light in weight, but expensive.

Parts /components of prosthesis:

Lower limb. Suspension system. Socket Knee setup Shin piece Foot piece.

Suspension system: The prosthesis is suspended by means of

following suspension systems;

In case of below knee prosthesis: supra condylar cuff (PTB) supra condylar wedge & walls (PTS) a thigh corset (BK)

Above knee prosthesis: 1. Socket is the important

part of the prosthesis which connects the stump to the prosthesis. The sockets are either carved or moulded

.knee setup it consists of knee block knee axis & a shank. The extension of the knee is limited to 180 degrees by the extension stop with in the unit. It should provide stability during the early & middle part of the stance phase & must allow bending during the latter part of stance & swing phase as well as in sitting & kneeling. It should be durable, comfortable & cosmetically acceptable.

I.e. they can be fabricated either by wood or by plastics.

If wood is used the distal end of the socket is open & continues to shank or shin. When plastic is used the distal end is covered.

There are two types of knee axis: Single axis unit, Polycentric knee. The advantage of polycentric knee over a

single axis knee is that it is more stable when loaded. It is employed for extremely short above knee stump or bilateral above knee amputation

Shin piece (Shank)

The shank of the prosthesis may be made entirely of wood except for its covering. Plastics/metal is used. It holds the foot ankle assembly and socket in a fixed relationship. The exterior finish of the wood shank is usually an appropriately colored plastic laminate.

This has the advantages over the glued raw hide covering. It provides:

greater strength moisture resistance Uniformity of colour.

Foot piece: The two most commonly used foot pieces are

– Single axis unit.– SACH foot.

Single axis unit: it consists of ankle joint which permits the movements around one axis. 15 degrees of PF & 5 degrees of DF.

This range is achieved by the action of PF bumper which corresponds to the action of the DF of the foot in the intact limb & by the action of the DF bumper corresponds to the action of the PF of the foot.

SACH/Rubber foot (Solid Ankle Cushion Heel)

It allows some motion in all directions. The cushion heel is available with different degrees of compressibility hard, medium & soft. It is selected on the basis of the amputation level, body built & ability to control prosthesis.

Advantages of SACH foot: It is simple Little maintenance Good appearance Quiet in operation Gait is near normal.

Double axis ankle:

Double axis ankle poses the same PF & DF as the single axis ankle. In addition it has a second axis which permits inversion & eversion of the foot.

There four motions permitted are limited by corresponding bumpers.

It accommodates better to uneven ground and permits greater stability in placement of the foot both in standing and walking.

The disadvantages are:

Bulkier Heavy Requires more maintenance Noisier

Prosthesis for Hemipelvectomy & Hip disarticulation amputations.

Hip disarticulation amputees comprise less than 2% of total amputee population. The two types of conventional limbs are

Saucer typeTilting table type.

Saucer type hip disarticulation prosthesis: It consists of a shallow socket (saucer type) hip joint

with pelvic band usually hip & knee lock is employed for better stability. Suspension by a pelvic band & single axis hip joint could be augmented by shoulder straps. The stump tends to rotate with in the shallow socket & the amputee sits directly on his buttocks thus maintaining his buttocks thus maintaining pelvis.

Tilting table prosthesis It is similar to the saucer type of prosthesis

except the design of the socket. A leather or plastic socket encases the stump & is suspended by a pelvic belt & occasionally a shoulder strap.

Canadian type H.D.P It is most commonly used. It is more functional better

looking and more comfortable than the saucer and tilting table types.

Design of the socket: the proximal brim of the socket is brought as high as the 10th rib. The opening for donning is made in the lateral wall on the unamputated side. The stump is rigidly continued by the thoracic cage.

Alignment of Canadian type Hip & knee joints of the Canadian type of prosthesis

are stabilized not only by the locks by unique arrangement of joint locations. The hip joint is located in front of the weight line. The knee joint is located behind the weight line.

A rubber hip extension stop is provided at the back of the thigh piece to avoid hyperextension of the prosthetic hip.

Prosthesis for knee disarticulation

The most common prosthesis used is end bearing prosthesis. But if the amputee is unable to bear weight at the distal end of the stump Ischial seat is provided to the socket.

Its socket may be either of flexible plastic (or) moulded by leather. The harnessing is by thigh lacer (or) buckle and strap (or) by the Velcro straps. The knee joint is attached to the medial & lateral side of the socket & continues to shank

Now a day’s piston type hydraulic swing phase control unit is also used in the knee joint. A SACH foot is generally used.

Disarticulation through the knee gives a stump advantages like:

It has a broad weight bearing area. The end bearing stump offers better

proprioceptive impulses & stability in walking.

Patellar tendon bearing below knee amputation

In PTB prosthesis no lace (thigh corset) & side hinges are used. It has the plastic socket which is designed such as 60% of the weight is born over the patellar tendon, rest of 40% is distributed over the condyles and posterior wall of the socket and it is suspended by a cuff suspension. A SACH foot piece is used.

The ideal length of the below knee stump is 5 inches from the knee joints. If the stump is too short PTB limb cannot be fitted. Then the PTS limb (or) below knee limb with slip socket is fitted to the short stump.

Patellar tendon supracondylar Prosthesis

This prosthesis is fitted to a very short stump. The anterior medial and lateral wall is higher than the PTB socket.

The patella is encapsulated into the socket. The posterior wall corresponds to the popliteal crease level. A SACH foot is used.

Below knee with slip socket

It consists of a thigh corset, a knee joint wooden oval socket with foot piece. In addition to the above components it consists of a leather slip socket which fits to the stump & slips into the wooden socket. Proximally it is attached to the thigh corset by elastic webbing.

The slip socket artificially extends the length of the stump. Hence it increases the leverage to move artificial limb.

Prosthesis for syme’s amputation

There are two types of prosthesis. Conventional syme’s prosthesis Canadian type syme’s prosthesis

Conventional syme’s prosthesis It consists of a long leather socket (corset

type) with anterior opening. It is reinforced with steel side bars. The harnessing is by the lacer system. The SACH foot is used.

Disadvantages: Cosmetically it is unacceptable It is heavy.

Canadian type symes Prosthesis It consists of resin (plastic) which is

reinforced by fiber glass. The opening with window is provided to the medial (or) posterior side of the socket. This opening is provided to insert, the bulbous end of the syme’s stump. The SACH foot is used.

Prosthesis for chopart’s amputation

A choparts boot is fitted. It is boot for which the ankle is covered. Back side opening is provided. The anterior toe portion is filled up be the cushion rubber.

Modern prosthesis

The utilization of plastics is one of the most important trends in modern prosthetics. They are of low temperature thermoplastics used now-a-days for the fabrication of the socket.

They are: Plastazote Aquaplast Bioplastics Orthoplast Glassona

These are in form of polyester sheet, some are in the form of synthetic rubber sheets, some are cellulose acetate plastic bandage form. These plastic characteristics especially in strength rigidly in appearance.

Modification of lower limb Prosthesis to suit Indian condition

Above knee Prosthesis modified to permit cross leg squatting.

In conventional above knee prosthesis, the thigh segment is made up of one single piece from hip to the knee joint, in the modified prosthesis the thigh segment consisting of two separate pieces, one upper & other lower with a turn table in between the two.

During walking the turn table is locked with the leg in neutral position. When he wants to squat, he unlocks the turn table and sits. In full squatting position, the distal segment is at 90 degrees of external rotation. When he gets up after extending the knee full, he internally rotates the distal segment manually and locks it in neutral position.

Below knee prosthesis modified for squatting with feet flat. The modifications in PTB prosthesis to make it squatting type

are The suspension cuff was suitably modified by providing elastic

piece in the middle of the cuff to accommodate the increase in circumference of the thigh segment in squatting.

The brim line of the posterior wall of the socket was lowered well below the popliteal crease by 1inch to 1 1/2inch. It was found that there was instability hence medial and lateral walls of the socket is also raised.

The posterior wall of the socket was made flexible to permit compression of the calf by the thigh

Madras foot

The madras foot is a foot piece developed at madras and used for lower limb prosthesis to facilitate bare foot walking. If the shoe is removed, the alignment of the prosthesis with respect to the body is disturbed. If the amputees attempts to walk without a shoe he will feel unstable.

Hence the SACH was modified as,

Extra rubber heel was provided so that the shin of the prosthesis is vertical with out shoe.

Shaped toes were provided for cosmetic acceptance.

Hind foot was shaped to have a tendo-achilles look.

Special sole was provided to with stand wear and tear due to prolonged walking.

Skin shade was given to match the color of the normal foot.

Bare foot has better grip on the floor surface than shaped foot. The amputees felt more confident to walk which reduces the training period.

Upper limb prosthesis

The prosthesis is prescribed according to the level of amputation and its residual function.

The Below elbow prosthesis consists of: The terminal device wrist unit fore-arm socket Below elbow hinges Harness Control cable system Cuffs and pads* “elbow unit” is used/ given for above elbow

prosthesis.

Terminal device: The purpose of the terminal device is to replace the grasp function of the hand.

It is divided into Hooks Hands Hooks: Commonly used terminal device is the split

type hooks. The amputee can open (or) close these hooks. The hooks are having 2 fingers. This finger like shape will permit the usual functions like holdings, carrying, pulling and pushing the objects.

There are two types of hooks available one is voluntary opening and the other one is voluntary closing. The voluntary opening type hooks are most commonly used. The hooks are operated by means of control cable system. The amputee exerts force on the control cable to open the fingers against the force of the rubber bands which acts as a spring to close the fingers to provide prehension of pinch force.

Hands: Hands may be divided into Cosmetic Hand voluntary closing hand voluntary opening hand Cosmetic glove which closely duplicate skin shape &

other features of the normal hand are used. The voluntary opening hands are most commonly

used and are available in various sizes. It has the mechanism of three jaw chuck by moving the thumb and first two fingers.

Wrist unit: The functions of the unit are used for attaching terminal device and its rotations (supination & pronation) to place the device in the best position to accomplish a desired activity.

Below elbow hinges: The function of below elbow hinges is to connect the socket to a cuff on the upper arm and is important for suspension and stability. These are variety of hinges.

Flexible hinge rigid hinge step up hinge

The flexible hinge is used for long below elbow amputee and wrist disarticulation where the sufficient voluntary pronation & supination are available. These flexible hinges will permit active pronation and supination of fore-arm as well as flexion and extension of the elbow.

Rigid hinges are utilized for short-below elbow cases where normal elbow flexion is present. Two types of rigid hinges are available single axis and polycentric.

Step up hinges are used together with a split socket prosthesis for very short below elbow cases where useable elbow flexion is limited. These hinges permit the stump to drive the prosthetic fore-arm through an increased ROM.

Cuffs and pads: Arm cuffs (or) triceps pads are used on the upper arm with the appropriate elbow hinges to connect the socket to the harness and help furnish socket suspension and stability. The triceps pad is used with long below elbow wrist disarticulation and transmetacarpel prosthesis. The arm cuff is used in the majority of short below elbow prosthesis.

Below elbow harness and control system: The functions of the below elbow harness are to suspend the prosthesis from shoulders. So the socket is firmly held on the stump. By using the body motions shoulder flexion & scapular abduction as source of power & transmits this form via cable system to operate the terminal device.

Myoelectric prosthesis

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