An Online Continuing Education ActivitySponsored By

Grant funds provided by

Principles of Bone Cement and the Process of Bone Cement MixingC

E O

NLI

NE

Welcome to

PrinCiPlES Of BOnECEmEnt And thE PrOCESS

Of BOnE CEmEnt mixing(An Online Continuing Education Activity)

COntinUing EdUCAtiOn inStrUCtiOnSThis educational activity is being offered online and may be completed at any time. Steps for Successful Course CompletionTo earn continuing education credit, the participant must complete the following steps:

1. Read the overview and objectives to ensure consistency with your own learning needs and objectives. At the end of the activity, you will be assessed on the attainment of each objective.

2. Review the content of the activity, paying particular attention to those areas that reflect the objectives.

3. Complete the Test Questions. Missed questions will offer the opportunity to re-read the question and answer choices. You may also revisit relevant content.

4. For additional information on an issue or topic, consult the references.5. To receive credit for this activity complete the evaluation and registration form. 6. A certificate of completion will be available for you to print at the conclusion.

Pfiedler Enterprises will maintain a record of your continuing education credits and provide verification, if necessary, for 7 years. Requests for certificates must be submitted in writing by the learner.

If you have any questions, please call: 720-748-6144.

COntACt infOrmAtiOn:

© 2014All rights reserved

Pfiedler Enterprises, 2101 S. Blackhawk Street, Suite 220, Aurora, Colorado 80014www.pfiedlerenterprises.com

Phone: 720-748-6144 Fax: 720-748-6196

3

OvErviEWFor the past 50 years, polymethylmethacrylate (PMMA) bone cements have been widely used as the anchoring/grouting agent in total joint replacements of the hip, knee, ankle, elbow, and shoulder. Good quality cement is essential for long-term implant survival and the role of the perioperative nurse in preparing that cement is vitally important. Strict adherence to good cement mixing and application techniques is a key factor in reducing the rate of loosening and also in increasing the long-term survival of the prosthesis. The purpose of this continuing education activity is to provide a review of key concepts regarding composition, properties, and types of bone cements and factors that affect bone cement polymerization. The evolution of mixing and application techniques also will be described. The activity concludes with a discussion of potential hazards posed by bone cement and safety considerations for patients and members of the surgical team.

OBJECtivES After completing this continuing nursing education activity, the participant should be able to:

1. Review the components of bone cement.2. Describe the types of bone cement available today. 3. Outline the history of bone cement mixing systems. 4. Differentiate the various bone cement mixing systems and application techniques. 5. Identify the safety issues related to the use of bone cement in the perioperative

practice setting.

intEndEd AUdiEnCE This continuing education activity is intended for perioperative registered nurses who are interested in learning more about bone cement and the process of bone cement mixing.

CrEdit/CrEdit infOrmAtiOnState Board Approval for NursesPfiedler Enterprises is a provider approved by the California Board of Registered Nursing, Provider Number CEP14944, for 2.0 contact hour(s).

Obtaining full credit for this offering depends upon completion, regardless of circumstances, from beginning to end. Licensees must provide their license numbers for record keeping purposes.

The certificate of course completion issued at the conclusion of this course must be retained in the participant’s records for at least four (4) years as proof of attendance.

IAHCSMMThe International Association of Healthcare Central Service Materiel Management has approved this educational offering for 2.0 contact hours to participants who successfully complete this program.

4

IACETPfiedler Enterprises has been accredited as an Authorized Provider by the International Association for Continuing Education and Training (IACET).

CEU Statements• As an IACET Authorized Provider, Pfiedler Enterprises offers CEUs for its

programs that qualify under the ANSI/IACET Standard.

• Pfiedler Enterprises is authorized by IACET to offer 0.2 CEUs for this program.

rElEASE And ExPirAtiOn dAtEThis continuing education activity was planned and provided in accordance with accreditation criteria. This material was originally produced in June 2014 and can no longer be used after June 2016 without being updated; therefore, this continuing education activity expires in June 2016.

diSClAimErAccredited status as a provider refers only to continuing nursing education activities and does not imply endorsement of any products.

SUPPOrtGrant funds for the development of this activity were provided by Cardinalhealth

AUthOrS/PlAnning COmmittEE/rEviEWErSusan K. Purcell littleton, COMedical Writer/Author

Julia A. Kneedler, rn, mS, Edd Aurora, COProgram Manager/ReviewerPfiedler Enterprises

Judith I. Pfister, RN, BSN, MBA Aurora, COProgram Manager/Planning CommitteePfiedler Enterprises

5

diSClOSUrE Of rElAtiOnShiPS With COmmErCiAl EntitiES fOr thOSE in A POSitiOn tO COntrOl COntEnt fOr thiS ACtivitYPfiedler Enterprises has a policy in place for identifying and resolving conflicts of interest for individuals who control content for an educational activity. Information listed below is provided to the learner, so that a determination can be made if identified external interests or influences pose a potential bias of content, recommendations or conclusions. The intent is full disclosure of those in a position to control content, with a goal of objectivity, balance and scientific rigor in the activity.

Disclosure includes relevant financial relationships with commercial interests related to the subject matter that may be presented in this educational activity. “Relevant financial relationships” are those in any amount, occurring within the past 12 months that create a conflict of interest. A “commercial interest” is any entity producing, marketing, reselling, or distributing health care goods or services consumed by, or used on, patients.

Activity Planning Committee/Authors/reviewers:

Julia A. Kneedler, rn, mS, Edd Co-owner of company that receives grant funds from commercial entities

Susan K. Purcell, mA No conflict of interest.

Judith I. Pfister, RN, BSN, MBA Co-owner of company that receives grant funds from commercial entities

6

PrivACY And COnfidEntiAlitY POliCYPfiedler Enterprises is committed to protecting your privacy and following industry best practices and regulations regarding continuing education. The information we collect is never shared for commercial purposes with any other organization. Our privacy and confidentiality policy is covered at our website, www.pfiedlerenterprises.com, and is effective on March 27, 2008.

To directly access more information on our Privacy and Confidentiality Policy, type the following URL address into your browse: http://www.pfiedlerenterprises.com/privacy-policy

In addition to this privacy statement, this Website is compliant with the guidelines for internet-based continuing education programs.

The privacy policy of this website is strictly enforced.

COntACt infOrmAtiOnIf site users have any questions or suggestions regarding our privacy policy, please contact us at:

Phone: 720-748-6144Email: registrar@pfiedlerenterprises.comPostal Address: 2101 S. Blackhawk Street, Suite 220 Aurora, Colorado 80014Website URL: http://www.pfiedlerenterprises.com

7

intrOdUCtiOnPolymethylmethacrylate (PMMA) bone cement is an essential component in many total joint arthroplasty procedures. In a cemented arthroplasty, the main functions of the cement are to immobilize the implant, transfer body weight and service loads from the prosthesis to the bone, and increase the load-carrying capacity of the prosthesis-bone cement-bone system. The term “cement,” however, is misleading since bone cement acts more like a grout, filling in space in order to create a tight space to hold the implant against bone. Good quality cement is essential for long-term implant survival and the role of the perioperative nurse in preparing that cement is vitally important. Accurate bone cement mixing and precise application techniques are critical to ensuring the stability and longevity of the prosthesis. Since bone cement is prepared and used in the operating room (OR) environment, it is important that all perioperative personnel recognize the unique safety considerations that are related to its preparation and its use.

COmPOnEntS Of BOnE CEmEntPMMA bone cements are usually supplied as two-component systems made up of a powder and a liquid. These two components are mixed at an approximate ratio of 2:1 to start a chemical reaction called polymerization, which forms the polymethylmethacrylate (PMMA) cement.

• Powder components1: ◦ Copolymers beads based on the substance polymethylmethacrylate (PMMA); ◦ Initiator, such as benzoyl peroxide (BPO), which encourages the polymer and

monomer to polymerize at room temperature; ◦ Contrast agents such as zirconium dioxide (ZrO2) or barium sulphate (BaSO4)

to make the bone cements radiopaque; and ◦ Antibiotics (eg, gentamicin, tobramycin).

• Liquid components2: ◦ A monomer, methylmethacrylate (MMA); ◦ Accelerator (N,N-Dimethyl para-toluidine) (DMPT); ◦ Stabilizers (or inhibitors) to prevent premature polymerization from exposure to

light or high temperature during storage; and ◦ Chlorophyll or artificial pigment; sometimes added to cements for easier

visualization in case of revision.

There is a difference between PMMA bone cement and PMMA; however, many healthcare personnel use the terms interchangeably and PMMA has become shorthand for “bone cement”. However, PMMA is the substance from which copolymers are derived for the powder component. When the copolymer powder is mixed with the MMA monomer liquid, polymerization occurs and PMMA bone cement is created.

8

POlYmEriZAtiOnPolymerization is a chemical reaction in which two or more small molecules combine to form larger molecules that contain repeating structural units of the original molecules. In the case of bone cement, the polymerization process starts when the copolymer powder and monomer liquid meet, reacting together to produce an initiation reaction creating free radicals that cause the polymerization of the monomer molecules. The original polymer beads of the powder are bonded into a dough-like mass, which eventually hardens into hard cement.

The polymerization process is an exothermic reaction, which means it produces heat. With a maximum in vivo temperature of 40°C to 47°C, this thermal energy is dissipated into the circulating blood, the prosthesis, and the surrounding tissue. Once polymerization ends, the temperature decreases and the cement starts to shrink.

Phases and TimesThe polymerization process can be divided into four different phases: mixing, waiting, working, and setting. Package inserts that come with the products often refer to Dough Time, Working Time, and Setting Time. Dough Time and Setting Time are measured from the beginning of mixing; Working Time is the interval between Dough Time and Setting Time. Both the Phases and corresponding Times are described below.

mixing PhaseThe mixing phase represents the time taken to fully integrate the powder and liquid. As the monomer starts to dissolve the polymer powder, the benzoyl peroxide is released into the mixture. This release of the initiator benzoyl peroxide and the accelerator DMPT is actually what causes the cement to begin the polymerization process. It is important for the cement to be mixed homogeneously, thus minimizing the number of pores.

Waiting Phase/dough timeDuring this phase, typically lasting several minutes, the cement achieves a suitable viscosity for handling (ie, can be handled without sticking to gloves). The cement is a sticky dough for most of this phase.

Dough time is the time point measured from the beginning of mixing to the point when the cement no longer sticks to surgical gloves. Under typical conditions (23°C-25°C, 65% relative humidity), dough time is 2-3 minutes after beginning of mixing for most bone cements. Before this time point, after the components are well mixed, the bone cement may be loaded into a syringe, cartridge, or injection gun for assisted application.3

Working Phase/Working timeThe working phase is the period during which the cement can be manipulated and the prosthesis can be inserted. The working phase results in an increase in viscosity and the generation of heat from the cement. The implant must be implanted before the end of the working phase.

9

Working time is the interval between the dough and setting times, typically 5-8 minutes. Previously, this represented the full time interval available for use of a particular mix of bone cement. The use of mechanical introduction tools, such as syringes and cartridges, extends this time by 1 to 1.5 min.4

Setting Phase/Setting timeDuring this phase, the cement hardens (cures) and sets completely, and the temperature reaches its peak. The cement continues to undergo both volumetric and thermal shrinkage as it cools to body temperature. Hardening is influenced by the cement temperature, the OR temperature, and the body temperature of the patient.

Setting time is the time point measured from the beginning of mixing until the time at which the exothermic reaction heats the cement to a temperature that is exactly halfway between the ambient and maximum temperature (ie, 50% of its maximum value), usually about 8-10 minutes. The temperature increase is due to conversion of chemical to thermal energy as polymerization takes place.5

Factors that Affect Dough, Working, and Setting TimesFactors that affect dough, working, and setting times include the following6:

• mixing Process – Mixing that is too rapid can accelerate dough time and is not desirable since it may produce a weaker, more porous bone cement.

• Ambient Temperature – Increased temperature reduces both dough and setting times approximately 5% per degree Centigrade, whereas decreased temperature increases them at essentially the same rate.

• humidity – High humidity accelerates setting time whereas low humidity retards it.

The combination of these factors is such that in a cold operating room on a very dry winter day, setting time may stretch out and raise concerns as to whether there is something wrong with the bone cement kit in use. There usually is not, but patience is required under these conditions. Water (or anything else) should never be added to bone cement in an attempt to modify its curing behavior.

Why Don’t All Cements Behave the Same?Despite the fact that basic PMMA bone cement materials are the same, the behavior of various cement products can be significantly different when they are mixed under similar conditions. There are several reasons for these differences:

• The polymer component of a number of cements is not purely PMMA. Some cement may contain PMMA copolymers such as methyl acrylate and styrene in the powder and additional polymers such as butyl methacrylate. All cements are labelled to show their ingredients.

• The ratio of the components and the overall powder-to-liquid ratio may differ between cements.

10

• The size, shape and weight of the polymer molecules can vary considerably.

• Manufacturing processes may differ.

• Sterilisation method may differ (eg, gamma, and ethylene oxide gas sterilisation).

CEmEnt PrOPErtiESCement properties critical for operating procedures, such as viscosity change, setting time, cement temperature, mechanical strength, shrinkage, and residual monomer, are determined during polymerization. These properties will influence cement handling, penetration, and interaction with the prosthesis. The most important properties are discussed below.

Cement PorosityPorosity is the fraction of the volume of an apparent solid that is actually empty space. High bone cement porosity compromises the cement’s mechanical strength and decreases its fatigue life. This may lead to aseptic loosening. Sources of porosity in cured bone cement include:

• Trapped air between the powder beads as the powder is wetted.

• Trapped air in the cement during mixing.

• Trapped air in the cement during transfer from mixing container to application device.

Hand mixing bone cement in an open bowl may introduce the greatest possibility of these occurrences, which is why hand-mixed cement can contain a substantial number of pores. Centrifugation and vacuum mixing methods, and pressurized cement application can decrease the porosity of bone cement.

Cement ViscosityViscosity is a measure of the resistance of a fluid to deformation under shear forces and is commonly described as “thickness” of a fluid. Viscosity also represents the resistance to flow and is thought to be a measure of fluid friction. Cement viscosity determines the handling and working properties of the cement.

Mixing together the powder and the liquid components marks the start of the polymerization process. During the reaction, the cement viscosity increases, slowly at first, then later more rapidly. During the working phase, there are two requirements for bone cement viscosity – it must be sufficiently low to facilitate the delivery of the cement dough to the bone site, and it must penetrate into the interstices of the bone.7 On the other hand, the viscosity of the bone cement should be sufficiently high to withstand the back-bleeding pressure, thus avoiding the risk of inclusion of blood into the cement because this could significantly reduce the stability of the bone cement. It is important that the cement retains an optimized viscosity for an adequate duration to allow a “comfortable” working time.8

11

Viscosity affects the following9:• Mixing behaviour;

• Penetration into cancellous bone;

• Resistance against bleeding; and

• Insertion of the prosthesis.

Cement TemperatureTo achieve optimal cement properties, it is important to adhere to the time schedules indicating the correlation of temperature to handling time. These time schedules are usually included in the manufacturer’s instructions for the bone cement.

Effects of Temperature:• Temperature affects mixing time, delivery of the cement, prosthesis insertion, and

other aspects of the cementing process.

• Storage temperature will affect the cement times – not just the temperature at which it is mixed.

• If cement has been stored in a cold environment, all the phases apart from the mixing phase will be prolonged. High-viscosity cements are sometimes pre-chilled for use with mixing systems for easier mixing and prolonged working phase. This will also increase the setting time.

• If cement has been stored in a warmer environment, all phases will be shorter.

• Issues created by high temperatures: ◦ Integration of the powder and liquid can be difficult. ◦ Extrusion from a delivery gun can become difficult and may reduce delivery

pressures. ◦ Potential exists for cement to be inserted during the setting phase. ◦ Laminations can form between 3.5 and 6.5 minutes and reduce cement

strength by up to 54%.10

Mechanical PropertiesThe aim of a good cement mix is to produce bone cement that has the best mechanical properties possible so that it can carry out its load transfer role successfully over the lifetime of the implant. Once positioned within the hip or knee replacement, the cement around the prosthesis is subjected to a series of physical forces that will have an effect on the lifespan of the cement. These physical forces subject the cement to fatigue, creep, and high stresses. The mechanical properties of the cement (eg, resistance to fatigue and creep, and strength) should be enhanced as much as possible.

12

fatigueFatigue is the failure of a component after it is subjected to a large number of alternating, fluctuating loads; fatigue strength is a measure of a bone cement’s durability. If applied only once, these loads would not be large enough to cause failure. A good example of this is a paper clip, which when bent once will not break, but after it has been bent a number of times, it will break easily.

As the cemented implant is subjected to not only static load but also dynamically alternating loads, the fatigue properties of the cement affect survival of the implant. Cement will have a natural lifespan and the repeated loads it is subjected to will, over time, cause it to break down and fail. It is the quality of the cement mix that will determine its lifespan. A well-mixed cement will be better equipped to deal with the loads placed upon it.

The ability of bone cement to resist fatigue is critical given the loads to which it will be subjected. Clinical evidence has documented the existence of fatigue cracks in revision-retrieved cement11,12 and in postmortem retrieved stem/cement/bone constructs.13 This suggests that the fatigue resistance of bone cement should be optimized to prevent fatigue failure.

CreepCreep is the deformation of a material under constant load. Under constant load, a material capable of creep will deform by an amount dependent on the size of the load and the length of time it is applied. Creep generally increases with temperature. Creep essentially is a mechanical problem that slowly and steadily can erode the long-term performance of an implant. Cements with higher porosity are less resistant to creep deformation.

Polymers are particularly susceptible to creep because of their molecular structure. Therefore, bone cement, as a polymer, is likely to exhibit creep as it is under a load and is at 37°C in the body.

Significant bone cement creep will lead to implant subsidence, which, in turn, may lead to failure.14 In the 1990s, a new formulation of bone cement had to be withdrawn after it was found to significantly creep, leading to implant subsidence, aseptic loosening, and high revision rates.15,16

Interestingly, a small degree of creep may in fact be advantageous in the early postoperative stages with some implant designs. A polished, tapered stem without a collar relies on some subsidence so that it becomes “wedged” in the bone cement, thereby improving the load transfer mechanism.17

StressStress is the load applied to a material over a given area. Stresses in the hip joint are a combination of compression, bending, and torsional (twisting) forces. As load is transferred during walking, the new joint and cement will be subjected to high stresses. If these high stresses exceed the strength of the cement, it will deform permanently and then, possibly, fail.

13

tYPES Of BOnE CEmEntCements can be grouped as high, medium, or low viscosity, with or without antibiotics.

The viscosity designation refers to the viscosity of the powder and liquid during the mixing phase: high-viscosity cement is dough-like, while low-viscosity cement is more like a liquid. The handling phases of different viscosity cements also vary considerably and the choice of which cement to use is often surgeon preference. For example, a 2006 national survey of 587 surgeons in the UK found that high-viscosity cement was used in total hip arthroplasty by 82% of the surgeons, medium-viscosity cement by 12%, and low-viscosity cement was used by 6%.18

High ViscosityHigh-viscosity bone cements have a short mixing phase and lose their stickiness quickly. This makes for a longer working phase. The viscosity remains constant until the end of the working phase. The setting phase lasts between one minute 30 seconds and two minutes.19 High-viscosity cements are associated with reduced revision rates for total hip arthroplasty.20

Medium ViscosityThese cements typically have a long waiting phase of three minutes, but during the working phase, the viscosity only increases slowly. Setting takes between one minute 30 seconds, and two minutes 30 seconds.21

Low ViscosityLow-viscosity cements have a long waiting phase of three minutes and the viscosity rapidly increases during the working phase, making for a short working phase. As a consequence, application of low-viscosity cements requires strict adherence to application times. The setting phase is one to two minutes long.22

Antibiotic CementsPeriprosthetic infection is the most feared complication in total hip and knee replacement. The infection usually leads to a complete failure of the joint replacement, resulting in a long series of operative procedures, great discomfort for the patient, and significant costs.

The use of antibiotic-impregnated bone cement to treat musculoskeletal infection has been reported in the literature for more than three decades despite the fact that it wasn’t until 2003 that the first pre-blended bone cement containing an antibiotic (tobramycin) became available for sale in the United States, specifically for the treatment and reimplantation of infected arthroplasties.23,24 Prior to 2003, U.S. surgeons prepared antibiotic cement on-site (ie, in the operating room) by adding antibiotic powder to the powdered bone cement prior to the addition of the liquid monomer. In Europe, however, pre-blended antibiotic bone cements have been available since the 1970s and the indications and scientific evidence for its use have expanded to primary arthroplasty to minimize postoperative infection. Use of antibiotic cements for primary arthroplasty,

14

however, remains controversial in the United States. The primary arguments proffered against the routine use of antibiotic bone cement are lack of efficacy, adverse effects on mechanical properties, increased costs, bacterial resistance, and systemic toxicity.25,26 However, there is significant evidence to refute these arguments.27,28,29

The elution of antibiotics from PMMA bone cement can be affected by certain factors including the type of cement used, preparation methods, surface characteristics, porosity of the cement, and the amount and/or type of antibiotics used.30

Not all antibiotics are suitable for use in bone cements. The following bacteriologic and physical and chemical factors should be considered in the choice of an antibiotic31:

• Preparation must be thermally stable and able to withstand the exothermic temperature of polymerization.

• Must have broad antimicrobial coverage.

• Must be available as a powder.

• Must have a low incidence of allergy.

• Must not significantly compromise mechanical integrity.

• Must elute from the cement over an appropriate period of time.

Gentamicin and tobramycin are the only antibiotics available in U.S. commercial antibiotic bone cement products; tobramycin is the most often used and studied antibiotic added to cement worldwide, but gentamicin is more common in the United States.32 Other antibiotics (singly or in combination with other antibiotics) that have been studied include vancomycin, cephalothin, clindamycin, meropenem, teicoplanin, ceftazidime, imipenem, piperacillin, and ciprofloxacin.33,34,35

hiStOrY Of BOnE CEmEnt mixing SYStEmSManual MixingUntil the 1980s, the composition and preparation of bone cement did not stray much from the standards introduced in 1959 by Sir John Charnley, a British orthopaedic surgeon who pioneered the hip replacement operation.36 Techniques for improving cement strength were not extensively tried.

Original mixing techniques were either hand- or bag-mixing. The liquid was injected into a powder bag and the two components were mixed by kneading. As mixing techniques evolved, an open bowl was used to mix the cement. The liquid and powder were poured into a plastic or stainless steel bowl and then mixed together with a spatula. A 1988 study by Linden of 46 samples of acrylic cement mixed by seven nurses found that a manual mixing technique lacks reproducibility and produces cements with uncontrollable porosity.37

Early in the use of open bowl mixing, exposure to the resulting noxious fumes created serious safety concerns. A certain amount of porosity in the final material remains unavoidable with conventional hand mixing techniques today, due to the air introduced

15

by stirring during hand spatulation. In order to reduce both the harmful fumes as well as the introduction of air into the cement mixture, the closed bowl technique, using a paddle mixing system and wall suction to evacuate the fumes, was developed.

VibrationDuring the 1980s, a vibrating mixing technique was introduced in hopes of improving bone cement properties. The results, however, were not convincing.38

CentrifugationIn this technique, cement was first mixed manually and then subjected to centrifugation to eliminate any air inclusions introduced during mixing and thus reduce porosity in hopes of improving compressing strength and handling properties. The technique required chilling the liquid monomer prior to mixing in order to negate the shortening effect of centrifugation on setting time. The resulting low-viscosity mixture then was introduced into a cement syringe, which was centrifuged at high speed for a short period of time. The method succeeded in reducing porosity but procedures varied significantly depending on the type of centrifugation and cement used.

Vacuum MixingAlso in the 1980s, mixing under vacuum was introduced to reduce exposure to fumes while also improving tensile strength and fatigue life of bone cement.39,40,41,42 After some refining, it produced better results than centrifugation, which was soon thereafter retired in favor of vacuum mixing43 and quickly became the preferred method of mixing. For example, a 2006 national survey of 587 surgeons in the UK found that 94% were using vacuum mixing systems for bone cement preparation with total hip arthroplasty.44

In most operating rooms today, bone cement is mixed under a vacuum, which results in a low porosity cement with increased strength and resistance to cement fatigue and creep. Trying to eliminate all of the porosity by using a very high vacuum level can promote excessive shrinkage and cracking.

With a vacuum mixing system, the cement is mixed in a syringe, bowl, or cartridge. All of these systems consist of an enclosed chamber connected to a vacuum source (eg, wall suction or a dedicated vacuum pump). All ingredients are added and mixed while the system is closed.

The methods for application of bone cement include hand packing, injection, and gun pressurization.

• hand packing – The original method for hip arthroplasty was hand packing, where cement in the femoral canal was finger packed. The proximal end was packed with cement by pressing with the fingers or thumbs; this pressurization forced the cement into the bone interstices. Cementing in total knee arthroplasty is still commonly hand-packed because the surfaces are readily visualized, which makes the application with pressure by hand feasible.

• injection – Syringes are used to apply, or inject, the cement.

16

• gun pressurization – Injection of the cement with a gun offers a mechanical advantage that allows the surgeon to force more cement into the interstices of the bone via higher pressurization. The pressurization tips of these devices allow more cement to be forced tightly into the bone while also preventing overflow.

SAfEtY iSSUES rElAtEd tO BOnE CEmEntThe components of PMMA bone cement (powder and liquid MMA monomer) are toxic and highly flammable. As a consequence, perioperative personnel must be aware of the potential hazards for both personnel and patients in the OR environment. Appropriate safety precautions must be implemented to reduce the risk of exposure and to monitor patient reactions closely. The specific hazards associated with the use of PMMA bone cement are described below.

Flammability/Combustion HazardsAs packaged, the product is considered stable. Nevertheless, the powder component is combustible and sensitive to static discharge. The liquid component is a volatile flammable liquid that slowly attacks rubber. The liquid will polymerize very readily and all contamination must be avoided, particularly organic peroxides, catalysts, free radicals generators and multivalent metal oxides, especially when wet. Heat and strong light, particularly fluorescent or UV, could cause polymerization.45 The operating room should be adequately ventilated to eliminate monomer vapors. Ignition of monomer vapors caused by the use of electrocautery devices in surgical sites near freshly implanted bone cement has been reported.46

Health Risks to Personnel47

Caution should be exercised during the mixing of the liquid and powder components of the PMMA bone cement to prevent excessive exposure to the concentrated vapors of the liquid methylmethacrylate (MMA) monomer, which may produce irritation of the respiratory tract, eyes, and possibly the liver. MMA fumes, which are emitted during preparation of PMMA bone cement, have been shown to have toxic side effects ranging from allergic reactions to neurological disorders. Although there is no evidence for potential carcinogenicity of the substance, all efforts should be made to reduce the exposure.48 The permissible exposure limit (PEL) value established by OSHA is a time-weighted average limit of 100 parts of MMA per million (ppm) of air or a time-weighted average of 410 milligrams of MMA per cubic meter of air during any 8-hour work shift in a 40-hour work week.49

Skin contact with the liquid monomer can cause contact dermatitis and hypersensitivity reactions. The MMA monomer is a powerful lipid solvent. It should not contact rubber or latex gloves. Double gloving or use of special gloves resistant to the monomer, and strict adherence to the mixing instructions may diminish the possibility of contact dermatitis and hypersensitivity reactions. The mixed PMMA bone cement should not contact the gloved hand until the cement has acquired the consistency of dough.

17

Eye contact with the liquid can be quite serious, causing considerable irritation or burns to the eyes. Soft contact lenses are very permeable and should not be worn where methylmethacrylate is being mixed because the lenses are subject to pitting and penetration by the vapors. Personnel wearing soft contact lenses should not mix PMMA bone cement or be nearby.

Health Risks to PatientsAccording to the U.S. Food and Drug Administration (FDA),

Serious adverse events, some with fatal outcome, associated with the use of the PMMA bone cement include myocardial infarction, cardiac arrest, cerebrovascular accident, and pulmonary embolism. The most frequent adverse reactions are transitory decreased blood pressure, elevated serum gamma-glutamyl-transpeptidase (GGTP) up to 10 days postoperation, thrombophlebitis, hemorrhage and hematoma, pain and/or loss of function, loosening or displacement of the prosthesis, superficial or deep wound infection, trochanteric bursitis, short-term cardiac conduction irregularities, heterotopic new bone formation, and trochanteric separation. Other potential adverse events associated with the use of PMMA bone cement include allergic pyrexia, hematuria, dysuria, bladder fistula, delayed sciatic nerve entrapment from extrusion of the bone cement beyond the region of its intended application, local neuropathy, local vascular erosion and occlusion, intestinal obstruction because of adhesions and stricture of the ileum from the heat released during the exothermic polymerization.50

Hypotensive reactions can occur between 10 and 165 seconds after application of the PMMA bone cement and can last for 30 seconds to 5 or more minutes. Some hypotensive reactions have progressed to cardiac arrest. The blood pressure of patients should be monitored carefully during and immediately following the application of the PMMA bone cement. In addition, overpressurization of the PMMA bone cement should be avoided during insertion of the PMMA bone cement and implant in order to minimize the occurrence of pulmonary embolism.51

Bone cement implantation syndrome (BCIS) is a poorly defined, poorly understood, rare, and potentially fatal intraoperative complication occurring in patients undergoing cemented orthopaedic surgeries.52,53 It can occur within minutes of the procedure; it also may be seen in the postoperative period in a milder form causing hypoxia and confusion. BCIS has no agreed upon definition; it is characterized by a number of clinical features that may include hypoxia, hypotension, cardiac arrhythmias, increased pulmonary vascular resistance (PVR), and cardiac arrest. It is most commonly associated with, but is not restricted to, hip arthroplasty. It usually occurs at one of the five stages in the surgical procedure; femoral reaming, acetabular or femoral cement implantation, insertion of the prosthesis, or joint reduction.54

18

rECOmmEndEd PrACtiCES fOr SAfE USE Of PmmA BOnE CEmEntThe Association of periOperative Registered Nurses (AORN) Recommended Practices for a Safe Environment of Care states that the potential hazards associated with the use of methylmethacrylate in the practice setting should be identified and safe practices should be established. Safe practices include the following measures55:

• Material safety data sheet (MSDS) information for methylmethacrylate must be readily accessible to employees within the practice setting. This information includes identification of hazards, precautions or special handling, signs and symptoms of toxic exposure, and first aid treatments for exposure. Methylmethacrylate should be handled according to its MSDS.

• Methylmethacrylate fumes should be extracted from the environment; the fumes should be exhausted to the outside air or absorbed through activated charcoal.

• Vacuum mixers with fume extraction should be used to decrease the fume levels to which users are exposed.

• Eye protection should be worn to prevent contact with eyes. Methylmethacrylate fumes may produce an adverse reaction with soft contact lenses, leading to irritation and potentially, corneal ulceration. There is no documented evidence of problems associated with hard contact lenses.

• The manufacturer’s recommendations should be followed for mixing and the required personal protective equipment (PPE).

• A second pair of gloves should be worn when handling methylmethacrylate and should be discarded after use. The manufacturer’s instructions should be followed regarding the composition of the second pair of gloves. Methylmethacrylate may be absorbed through the skin and may also penetrate many plastic and latex compounds, leading to dermatitis. The liquid component of the cement should not come in contact with gloves.

• A cement gun or mixing system, instead of hand mixing, should be used to decrease handling of the product. The cement mixture should not be touched until it is the consistency of dough.

• For methylmethacrylate spills: ◦ The area of the spill should be ventilated until the odor has dissipated; ◦ All sources of ignition should be removed; ◦ Appropriate PPE should be worn during the clean-up; ◦ The spill area should be isolated; ◦ The liquid component should be covered with an activated charcoal absorbent; and ◦ The waste product should be disposed of in a hazardous waste container.

• Methylmethacrylate is a hazardous waste and should be disposed of according to state, local, and federal regulations.

19

SUmmArYPMMA bone cement has been used in cemented arthroplasty procedures for over 50 years. Good quality cement is essential for long-term implant survival and the role of the perioperative nurse in preparing that cement is vitally important. The quality of bone cement is determined by several factors, including the type of cement selected, (ie, viscosity, presence of antibiotics) and strict adherence to instructions provided by the manufacturer. Its effectiveness is highly dependent upon the use of optimal mixing and application techniques. The components of PMMA bone cement (powder and liquid MMA monomer) are toxic and highly flammable. As a consequence, perioperative personnel must be aware of the potential hazards for both personnel and patients in the OR environment. Appropriate safety precautions must be implemented to reduce the risk of exposure and to monitor patient reactions closely.

20

glOSSArYAccelerator A catalytic agent used to hasten a chemical

reaction.

Bone Cement implantation A rare complex of sudden physiologic changes Syndrome (BCiS) characterized by hypoxia, hypotension or both and/or unexpected loss of consciousness occurring around the time of cementation, prosthesis insertion, reduction of the joint or, occasionally, limb tourniquet deflation in a patient undergoing cemented bone surgery. Symptoms may occur within minutes of the use of PMMA cement.

Compressive Strength The measure of bone cement’s durability during weight bearing.

Copolymer A polymer derived from two or more monomers.

Creep The measure of bone cement’s reaction to a combination of compressive and shear forces that occur during a variety of normal activities of daily living over time.

dough time The time point measured from the beginning of mixing to the point when the cement no longer sticks to surgical gloves.

Exothermic reaction A chemical reaction that produces heat.

fatigue The failure of a component after it is subjected to a large number of alternating, fluctuating loads.

high-viscosity Cements Cements that have a short waiting/sticky phase and a long working phase. The viscosity remains constant until the end of the working phase.

laminations Faults or folds in the bone cement, which may be caused by high temperature or “intrusions” such as bone, water, blood, etc. Laminations create potential areas of weakness in the cement mantle where a failure can occur.

21

low-viscosity Cements Cements that have a long waiting phase of about 3 minutes; the viscosity rapidly increases during the working phase, making for a short working phase.

medium-viscosity Cements Cements that have a long waiting phase of approximately 3 minutes, but during the working phase, the viscosity only increases slowly.

methylmethacrylate (mmA) The liquid component of bone cement; MMA is a monomer.

mixing Phase The phase in which the monomer is thoroughly mixed throughout the powder bed and polymerization is initiated.

monomer A molecule of low molecular weight capable of reacting with identical or different molecules of low molecular weight to form a polymer. For bone cement, the monomer MMA (a liquid) reacts with the copolymers based on PMMA to form PMMA bone cement.

Parts per million (ppm) “Parts per million” refers to a substance per million parts of air; it is a measure of the substance’s concentration of volume in air.

Permissible Exposure Limit (PEL) The permissible exposure limit of a hazardous substance, which is enforceable by OSHA.

Polymerization The formation of a compound, usually of high molecular weight, by the combination of several low molecular weight compounds (eg, monomers, copolymers).

Polymethylmethacrylate (PmmA) PMMA is a synthetic acrylic resin used as the basis for PMMA bone cement. Bone cement consists of two primary components: a powder consisting of copolymers based on polymethylmethacrylate (PMMA), and a liquid monomer, methylmethacrylate (MMA).

22

Porosity The presence of entrapped air in bone cement. High bone cement porosity compromises the cement’s mechanical strength and decreases its fatigue life. Centrifugation and vacuum mixing methods, and pressurized cement application can decrease the porosity of bone cement.

Setting Phase The final curing state of the polymerization process of bone cement; the implant should already be in its final position.

Setting time Time point from the beginning of mixing until the time at which the exothermic reaction heats the cement to a temperature that is exactly halfway between the ambient and maximum temperature (ie, 50% of its maximum value), usually about 8-10 minutes.

Stress The load applied to a material over a given area.

viscosity A measure of the resistance of a fluid to deformation under shear forces and is commonly described as “thickness” of a fluid. The viscosity of bone cement affects its handling characteristics, handling time, and penetration of the cement into the cancellous bone.

Waiting Phase The phase of the polymerization process where bone cement begins to swell and viscosity begins to increase, creating a sticky dough. By the end of the waiting phase, the doughy cement will not stick to surgical gloves.

Working Phase The time during the polymerization process at which bone cement is ready for application; the implant must be implanted before the end of the working phase.

Working time The interval between the dough and setting times, typically 5-8 minutes.

23

rEfErEnCES1. Ashari R. Science of Bone Cement. http://www.healio.com/orthopedics/hip/news/

online/%7B99ce957f-8cff-4cf7-8dad-ce12ae16658c%7D/science-of-bone-cement. Accessed January 19, 2014.

2. Ashari R. Science of Bone Cement. http://www.healio.com/orthopedics/hip/news/online/%7B99ce957f-8cff-4cf7-8dad-ce12ae16658c%7D/science-of-bone-cement. Accessed January 19, 2014.

3. Ong KL, Lovald S, Black J. Orthopaedic Biomaterials in Research and Practice. 2nd ed. Hoboken, NJ: Taylor & Francis; 2013.

4. Ong KL, Lovald S, Black J. Orthopaedic Biomaterials in Research and Practice. 2nd ed. Hoboken, NJ: Taylor & Francis; 2013.

5. Ong KL, Lovald S, Black J. Orthopaedic Biomaterials in Research and Practice. 2nd ed. Hoboken, NJ: Taylor & Francis; 2013.

6. Ong KL, Lovald S, Black J. Orthopaedic Biomaterials in Research and Practice. 2nd ed. Hoboken, NJ: Taylor & Francis; 2013.

7. Ashari R. Science of Bone Cement. http://www.healio.com/orthopedics/hip/news/online/%7B99ce957f-8cff-4cf7-8dad-ce12ae16658c%7D/science-of-bone-cement. Accessed January 19, 2014.

8. Ashari R. Science of Bone Cement. http://www.healio.com/orthopedics/hip/news/online/%7B99ce957f-8cff-4cf7-8dad-ce12ae16658c%7D/science-of-bone-cement. Accessed January 19, 2014.

9. Bone cement: properties. http://www.bonecement.com/cementing-techniques/bonecement/properties. Accessed January 19, 2014.

10. Gruen TA, Markolf KL, Amstutz HC. Effects of laminations and blood entrapment on the strength of acrylic bone cement. Clinical Orthopaedics and Related Research. 1976;(119):250-255.

11. Culleton P, Prendergast PJ, Taylor D. Fatigue failure in the cement mantle of an artificial hip joint. Clinical Materials. 1993;12(2):95-102.

12. Topoleski LD, Ducheyne P, Cuckler JM. A fractographic analysis of in vivo poly(methyl methacrylate) bone cement failure mechanisms. Journal of Biomedical Materials Research: Part B Applied Biomaterials. 1990;24(2):135-154.

13. Jasty M, Maloney WJ, Bragdon CR, O’Connor DO, Haire T, Harris WH. The initiation of failure in cemented femoral components of hip arthroplasties. Journal of Bone and Joint Surgery. 1991;73(4):551-558.

14. Norman TL, Shultz T, Noble G, Gruen TA, Blaha JD. Bone creep and short and long term subsidence after cemented stem total hip arthroplasty (THA). Journal of Biomechanics. 2013 15;46(5):949-955.

24

15. Thanner J, Freij-Larsson C, Kärrholm J, Malchau H, Wesslén B. Evaluation of Boneloc. Chemical and mechanical properties, and a randomized clinical study of 30 total hip arthroplasties. Acta Orthopaedica Scandinavica. 1995;66(3):207-214.

16. Havelin LI, Espehaug B, Lie SA, Engesaeter LB, Furnes O, Vollset SE. Prospective studies of hip prostheses and cements. A presentation of the Norwegian Arthroplasty Register 1987–1999. Meeting of the American Academy of Orthopaedic Surgeons; March 15–19; Orlando FL. 2000.

17. Ling RS. The use of a collar and precoating on cemented femoral stems is unnecessary and detrimental. Clinical Orthopaedics and Related Research. 1992;(285):73-83.

18. Nedungayil SK, Mehendele S, Gheduzzi S, Learmonth ID. Femoral cementing techniques: urrent trends in the UK. Annals of the Royal College of Surgeons of England. 2006;88(2):127-130.

19. Webb JC, Spencer RF. The role of polymethylmethacrylate bone cement in modern orthopaedic surgery. Journal of Bone and Joint Surgery. 2007;89(7):851-857. http://www.bjj.boneandjoint.org.uk/content/89-B/7/851.full.pdf+html. Accessed January 19, 2014.

20. Havelin LI, Espehaug B, Lie SA, Engesaeter LB, Furnes O, Vollset SE. Prospective studies of hip prostheses and cements. A presentation of the Norwegian Arthroplasty Register 1987–1999. Meeting of the American Academy of Orthopaedic Surgeons; March 15–19; Orlando FL. 2000.

21. Webb JC, Spencer RF. The role of polymethylmethacrylate bone cement in modern orthopaedic surgery. Journal of Bone and Joint Surgery. 2007;89(7):851-857. http://www.bjj.boneandjoint.org.uk/content/89-B/7/851.full.pdf+html. Accessed January 19, 2014.

22. Webb JC, Spencer RF. The role of polymethylmethacrylate bone cement in modern orthopaedic surgery. Journal of Bone and Joint Surgery. 2007;89(7):851-857. http://www.bjj.boneandjoint.org.uk/content/89-B/7/851.full.pdf+html. Accessed January 19, 2014.

23. Duey RE, Chong AC, McQueen DA, et al. Mechanical properties and elution characteristics of polymethylmethacrylate bone cement impregnated with antibiotics for various surface area and volume constructs. Iowa Orthopaedic Journal. 2012;32:104-115.

24. Parvizi J, Saleh KJ, Ragland PS, Pour AE, Mont MA. Efficacy of antibiotic-impregnated cement in total hip replacement. Acta Orthopaedica. 2008;79(3):335-341.

25. Clyburn TA, Cui Q. Antibiotic laden cement: current state of the art. http://www.aaos.org/news/bulletin/may07/clinical7.asp. Accessed January 20, 2014.

25

26. Joseph TN, Chen AL, Di Cesare PE. Use of antibiotic-impregnated cement in total joint arthroplasty. Journal of the American Academy of Orthopaedic Surgeons. 2003;11(1):38-47.

27. Illingworth KD, Mihalko WM, Parvizi J, Sculco T, McArthur B, el Bitar Y, Saleh KJ. How to minimize infection and thereby maximize patient outcomes in total joint arthroplasty: a multicenter approach: AAOS exhibit selection. Journal of Bone and Joint Surgery (American volume). 2013;95(8):e50.

28. Dunbar MJ. Antibiotic bone cements: their use in routine primary total joint arthroplasty is justified. Orthopedics. 2009;32(9). http://www.healio.com/orthopedics/knee/journals/ortho/%7B8f1efbbf-72b0-4e57-8ce2-a14130debf07%7D/antibiotic-bone-cements-their-use-in-routine-primary-total-joint-arthroplasty-is-justified#. Accessed January 19, 2014.

29. Wang J, Zhu C, Cheng T, Peng X, Zhang W, et al. (2013) A systematic review and meta-analysis of antibiotic-impregnated bone cement use in primary total hip or knee arthroplasty. PLoS ONE. 2013;8(12): e82745. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0082745;jsessionid=2A9DEFF892354BA15DB06028ECF82F0F. Accessed January 20, 2014.

30. Duey RE, Chong AC, McQueen DA, et al. Mechanical properties and elution characteristics of polymethylmethacrylate bone cement impregnated with antibiotics for various surface area and volume constructs. Iowa Orthopaedic Journal. 2012;32:104-115.

31. University of Illinois at Chicago, College of Pharmacy. FAQ: Antibiotic impregnated cement and beads – an overview. http://www.uic.edu/pharmacy/services/di/faq/antibiotic_impregnated.php. Accessed January 18, 2014.

32. Clyburn TA, Cui Q. Antibiotic laden cement: current state of the art. http://www.aaos.org/news/bulletin/may07/clinical7.asp. Accessed January 20, 2014.

33. Lewis G. Properties of antibiotic-loaded acrylic bone cements for use incemented arthroplasties: a state-of-the-art review. Journal of Biomedical Materials Research: Part B Applied Biomaterials. 2009;89(2):558-574.

34. Baleani M, Persson C, Zolezzi C, Andollina A, Borrelli AM, Tigani D. Biological and biomechanical effects of vancomycin and meropenem in acrylic bone cement. Journal of Arthroplasty. 2008;23(8):1232-1238.

35. Chang Y, Tai CL, Hsieh PH, Ueng SW. Gentamicin in bone cement: A potentially more effective prophylactic measure of infection in joint arthroplasty. Bone and Joint Research. 2013 15;2(10):220-226.

36. Vacuum mixing and delivery: History. http://www.bonecement.com/cementing-techniques/mixingdelivery/history. Accessed January 19, 2014.

37. Lindén U. Porosity in manually mixed bone cement. Clinical Orthopaedics and Related Research. 1988;(231):110-112.

26

38. Lindén U. Mechanical properties of bone cement. Importance of the mixing technique. Clinical Orthopaedics and Related Research. 1991;(272):274-278.

39. Lidgren L, Drar H, Moller J. Strength of polymethylmethacrylate increased by vacuum mixing Acta Orthopaedica Scandinavica. 1984;55(5): 536–541.

40. Lidgren L, Bodelind B, Möller J, Bone cement improved by vacuum mixing and chilling, Acta Orthopaedica Scandinavica. 1987;58(1):27-32.

41. Alkire MJ, Dabezies EJ, Hastings PR. High vacuum as a method of reducing porosity of polymethylmethacrylate. Orthopedics. 1987;10(11):1533-1539.

42. Mau H, Schelling K, Heisel C, Wang JS, Breusch SJ. Comparison of various vacuum mixing systems and bone cements as regards reliability, porosity and bending strength. Acta Orthopaedica Scandinavica. 2004;75(2):160-172.

43. Vacuum mixing and delivery: history. http://www.bonecement.com/cementing-techniques/mixingdelivery/history. Accessed January 19, 2014.

44. Nedungayil SK, Mehendele S, Gheduzzi S, Learmonth ID. Femoral cementing techniques: current trends in the UK. Annals of the Royal College of Surgeons of England. 2006;88(2):127-130.

45. DePuy CMW Material Safety Data Sheet. Unmedicated Bone Cements. 2007. http://www.depuy.com/sites/default/files/products/files/DO_Unmedicated_Bone_Cements_MSDS.pdf. Accessed January 22, 2014.

46. U.S. Food and Drug Administration [FDA]. Medical Devices; Reclassification of Polymethylmethacrylate (PMMA) Bone Cement. Federal Register. 2002;67(137):46852-46855. Codified at 21 CFR §888. http://www.fda.gov/ohrms/dockets/98fr/071702c.htm. Accessed January 20, 2014.

47. U.S. Food and Drug Administration [FDA]. Medical Devices; Reclassification of Polymethylmethacrylate (PMMA) Bone Cement. Federal Register. 2002;67(137):46852-46855. Codified at 21 CFR §888. http://www.fda.gov/ohrms/dockets/98fr/071702c.htm. Accessed January 20, 2014.

48. Schlegel UJ, Sturm M, Eysel P, Breusch SJ. Pre-packed vacuum bone cement mixing systems. A further step in reducing methylmethacrylate exposure in surgery. Annals of Occupational Hygiene. 2010;54(8):955-961.

49. U.S. Department of Labor, OSHA. Chemical sampling information: methyl methacrylate. Chemical Sampling Information: Methyl methacrylate. https://www.osha.gov/dts/chemicalsampling/data/CH_254400.html. Accessed January 20, 2014.

50. U.S. Food and Drug Administration [FDA]. Medical Devices; Reclassification of Polymethylmethacrylate (PMMA) Bone Cement. Federal Register. 2002;67(137):46852-46855. Codified at 21 CFR §888. http://www.fda.gov/ohrms/dockets/98fr/071702c.htm. Accessed January 20, 2014.

27

51. U.S. Food and Drug Administration [FDA]. Medical Devices; Reclassification of Polymethylmethacrylate (PMMA) Bone Cement. Federal Register. 2002;67(137):46852-46855. Codified at 21 CFR §888. http://www.fda.gov/ohrms/dockets/98fr/071702c.htm. Accessed January 20, 2014.

52. Donaldson AJ, Thomson HE, Harper NJ, Kenny NW. Bone cement implantation syndrome. British Journal of Anaesthesia. 2009;102(1):12-22.

53. Razuin R, Effat O, Shahidan MN, Shama DV, Miswan MF. Bone cement implantation syndrome. Malaysian Journal of Pathology. 2013;35(1):87-90.

54. Donaldson AJ, Thomson HE, Harper NJ, Kenny NW. Bone cement implantation syndrome. British Journal of Anaesthesia. 2009;102(1):12-22.

55. AORN. Recommended practices for a safe environment of care. In: Perioperative Standards and Recommended Practices. Denver, CO: AORN, Inc;2013;217-242.

28

Please click here for thePost-Test and Evaluation