Preparation and Safe Use of PMMA Bone Cement
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Preparation and Safe Use of PMMA Bone Cement (An Online Continuing Education Activity) CONTINUING EDUCATION INSTRUCTIONS This educational activity is being offered online and may be completed at any time.
STEPS FOR SUCCESSFUL COURSE COMPLETION To 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.
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Preparation and Safe Use of PMMA Bone Cement Overview Polymethylmethacrylate (PMMA), commonly referred to as bone cement, continues to play a vital role as one of the primary synthetic biomaterials used in orthopedic surgery. The safe and effective use of bone cement is a critical factor in the success of many total joint arthroplasty procedures today. Accurate cement mixing and precise application techniques both increases the stability and the longevity of the prosthesis. Therefore, these techniques are the foundation of successful outcomes for the patient undergoing cemented arthroplasty procedures. In addition, safe handling of PMMA in the operating room is essential to ensure that the potential associated health risks both to patients and healthcare workers are minimized. Therefore, it is critical that perioperative personnel involved in the preparation and use of PMMA bone cement are aware of these potential risks and that they handle bone cement in a manner that minimizes them. This continuing education activity will provide a review of the key clinical considerations related to the preparation and safe use of PMMA bone cement. The historical evolution of the development of bone cement and the progressive advances briefly will be reviewed. The science of bone cement, including its components and the various types of cement, such as antibiotic impregnated cement, will be discussed. The indications and contraindications for the use of bone cement and the key criteria for patient selection, as well as the appropriate type of bone cement, will be outlined. The evolution of mixing and application techniques also will be presented. The potential hazards associated with the use of bone cement, including bone cement implantation syndrome, will be discussed. This will be followed by a review of key measures for the safe use of bone cement which will reduce the risk of exposure in both patients and members of the surgical team.
Upon completion of this continuing education activity, the participants should be able to:
1. Discuss the historical evolution of the development and use of bone cement. 2. Describe the components of bone cement and the various types available today. 3. Outline the indications and contraindications for the use of bone cement. 4. Describe various cement mixing and application techniques. 5. Identify the hazards associated with the use of PMMA in the perioperative practice setting. 6. Discuss key safety precautions that are required to prevent excessive exposure to PMMA ingredients both in patients and healthcare workers.
Intended Audience This continuing education activity is intended for perioperative nurses, surgical technologists, and other health care professionals who are involved in the care of patients undergoing cemented total joint arthroplasty. This study guide will assist those who are interested in learning more about the key safety considerations in the preparation and use of PMMA bone cement.
CREDIT/CREDIT INFORMATION State Board Approval for Nurses
Pfiedler 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 attendance, 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. 1
AST Credit for Certified Surgical Technologists/Certified Surgical First Assistant
This continuing education activity is approved for 4.5 CE credits by the Association of Surgical Technologists, Inc., for continuing education for the Certified Surgical Technologists and Certified Surgical First Assistant. This recognition does not imply that AST approves or endorses any product or products that are discussed or mentioned in enduring material.
IACET Credit for Allied Health Professionals
Pfiedler Enterprises has been approved as an Authorized Provider by the International Association for Continuing Education and Training (IACET), 1760 Old Meadow Road, Suite 500, McLean, VA 22102, (703) 506-3275. CEU STATEMENT As an IACET Authorized Provider, Pfiedler Enterprises offers CEUs for its programs that qualify under IACET guidelines. Pfiedler Enterprises is authorized by IACET to offer 0.2 CEUs (2.0 contact hours) for this program.
RELEASE AND EXPIRATION DATE This continuing education activity was planned and provided in accordance with accreditation criteria. This material was originally produced in September 2013 and can no longer be used after September 2015 without being updated; therefore, this continuing education activity expires in September 2015.
DISCLAIMER Pfiedler Enterprises does not endorse or promote any commercial product that may be discussed in this activity.
SUPPORT Grant funds for the development of this activity were provided by Stryker.
AUTHORS/PLANNING COMMITTEE/REVIEWER Rose Moss, MN, RN, CNOR Elizabeth, CO Nurse Consultant/Author Moss Enterprises Julia A. Kneedler, RN, MS, EdD Aurora, CO Program Manager/Reviewer Pfiedler Enterprises Judith I. Pfister, RN, BSN, MBA Program Manager/Planner Pfiedler Enterprises
Donna Reeves, BA, MA, MEd, PhD Aurora, CO Consultant/Reviewer
DISCLOSURE OF RELATIONSHIPS WITH COMMERCIAL ENTITIES FOR THOSE IN A POSITION TO CONTROL CONTENT FOR THIS ACTIVITY Pfiedler 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: Rose Moss, MN, RN, CNOR No conflict of interest Julia A. Kneedler, RN, MS, EdD Co-owner of company that receives grant funds from commercial entities Judith I. Pfister, RN, BSN, MBA Co-owner of company that receives grant funds from commercial entities Donna Reeves, BA, MA, MEd, PhD No conflict of interest
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Introduction Polymethylmethacrylate (PMMA), commonly known as bone cement, is a widely used method of implant fixation; this technique has largely contributed to the success of modern joint replacement.1 As will be discussed, “cement” is a misnomer because, in general, the word cement is used to describe a substance that bonds two things together.2 Thus the term cement implies that the material sticks the implant into the bone; in reality, however, PMMA should be called bone “grout”, because it acts as a space-filler that creates a tight space which holds the implant against the bone. Bone cement is the only implant that is manufactured in the operating room (OR). None the less, it must meet the same high standards that are demanded of any other implant supplied by the industry.3 In addition, due to its composition, PMMA has unique safety considerations that are related to its preparation and its use in the OR. Accurate bone cement mixing and precise application techniques are the foundation of successful patient outcomes, as they both increase the stability and the longevity of the prosthesis. Also, safe handling of PMMA bone cement is critical in ensuring that the potential health risks to both patients and healthcare professionals are minimized.
Historical Evolution of Bone Cement The development of bone cement has played a key role in refining and improving surgical techniques for cemented total joint arthroplasty. Since its development, the widespread use of bone cement has contributed to successful joint replacement and patient outcomes. Cementing with self-curing substances was the first, and initially the only, technique to achieve a stable fixation of the implants. Themistokles Gluck, a German surgeon, was the first surgeon to implant a total knee prosthesis made of ivory in 1870. He fixed the stems in both the tibia and the femur with a cement that he mixed of plaster and colophony, which cured up to the hardness of glass.4 Dr. Otto Rohm first synthesized a group of thermoplastics, ie, acrylic polymers, and introduced them into commercial use in the 1930’s. In their earliest applications, these acrylics replaced hard rubber as the base materials for dentures.5 Sir John Charnley, is considered the founder of modern artificial joint replacement. He developed the art and science of modern cementing technique in the late 1950’s, as he searched for ways to fix the femoral component as part of the development of his low friction arthroplasty.6 Dr. Charnley wanted a material that was resistant to body fluids, viscous with a low toxicity, could be easily manipulated, and would set within a reasonable time. After experimenting with various materials, he eventually settled on polymethylmethacrylate – a viscous dough which he formed by mixing the powder with the liquid monomer. Dr. Charnley used cold-cured PMMA to attach an acrylic cup to the femoral head and to seat a metallic femoral prosthesis; this was a significant milestone in the advancement of orthopedic surgical procedures. Also, Dr. Charnley was the first to realize that PMMA easily could be used to fill the medullary canal and to blend with the bone morphology. The cement served to increase the biomechanical stability and to decrease the stress on the implant; he settled on the idea of using cement as a “grout” for the hip implants. In the 1960’s, bone cement was not available widely in the United States because it was not approved for use in total hip surgery. In the 1970’s, the U.S. Food and Drug Administration (FDA) approved bone cement for use in hip and knee prosthetic fixation.7 Since then, while bone cement has become widely used for fixation of prostheses to living bone, the trends of bone cement use have evolved.8 Also in the early 1970’s, an infection rate of over 7% led to addition of antibiotics to the bone cement.9 At that time, the aminoglycosides proved to be the best and most practical antibiotics, because of their antibiotic spectrum and also because of their chemical properties. For example, gentamicin exhibits extreme stability during sterilization procedures, manufacturing processes, and over its shelf life; furthermore, it is resistant to the temperatures that occur during the polymerization process, and it is readily delivered from the polymers, moreover it acts locally in high concentrations without any systemic adverse effects. In the 1970’s, cement was preferred, as clinicians were pleased with the application and results of this new technique; in the 1980’s, cementless fixation techniques were preferred. During the 1990’s and into the present, hybrid systems are
preferred. For example, many of today’s total hip arthroplasty procedures use a cemented femur and a press-fit acetabulum prosthesis; total knee arthroplasties use a cemented tibia and a patella with a press-fit femur prosthesis. On May 6, 2003, the Center for Devices and Radiological Health (CDRH) of the U.S. FDA cleared the first antibiotic bone cement preparation.10 The FDA noted that the indication for use of this product was for the fixation of prostheses to living bone for use in the second stage of a two-stage revision for total joint arthroplasty. This was an important hallmark in the evolution of bone cement, as the pre-blended product ensures consistency and uniformity of the antibiotic/cement mixture. Antibiotic bone cements are used to prevent or to treat infections by eluting the antibiotic locally into the targeted tissues. Local delivery of antibiotic reduces the potential for systemic toxicity and other adverse side effects. Worldwide, Tobramycin is used most often and it is the most studied bone cement antibiotic. However, Gentamicin use is more common in the United States.11 Both of these antibiotics are acceptable because they are available in powder form, thermostable, safe, provide broad antimicrobial coverage, and they have a low incidence of allergic reactions. Gentamicin and tobramycin are the only antibiotics available in commercial antibiotic laden bone cement; however, other antibiotics including vancomycin and cephalothin have been studied. The historical evolution of bone cement is summarized in Table 1. Table 1 – Historical Evolution of Bone Cement Year 1870
Development Themistokles Gluck First surgeon to implant a total knee prosthesis made of ivory in Germany The stems were fixed with cement mixed of plaster and colophony
Otto Rohm Synthesized a group of thermoplastics, ie, acrylic polymers These polymers replaced hard rubber as the base materials for dentures
Sir John Charnley Developed the modern cementing technique Used cold-cured PMMA to attach an acrylic cup to the femoral head and to seat a metallic femoral prosthesis First to realize that PMMA could be used to fill the medullary canal and to blend with the bone morphology
U.S. FDA Approved bone cement for use in hip and knee prosthetic fixation Cement was the preferred technique for total joint fixation
Cementless fixation techniques were preferred
Hybrid systems are the preferred technique
U.S. FDA Cleared the first antibiotic bone cement preparation 5
PMMA Bone Cement: What Is It? Overview In order to use PMMA safely and effectively, it is important to review its components. Polymethylmethacrylate is an acrylic polymer that is formed by mixing two sterile components: a liquid methylmethacrylate monomer and a powered methylmethacyrlate-styrene co-polymer.12 The polymer component, is a finely divided white powder, and primarily it consists of beadshaped particles with a diameter typically of 40 microns. These particles contain, in addition to homopolymer PMMA and/or methyl methacrylate (MMA) copolymers, one of the three activators of the polymerization process: benzoyl peroxide (BPO) (so-called initiator); zirconia (ZrO2), or barium sulphate (BaSO4) to provide radiodensity; and an antibiotic.13 The liquid, as the second component, mainly contains the monomer MMA and it is the second activator of the polymerization process, N,N-Dimethyl para-toluidine (DMPT) (ie, the so called accelerator) DMPT, and hydroquinone act as a stabilizer to prevent self-curing of the monomer in the liquid during storage (see Table 2). When the two components are mixed, the liquid monomer polymerizes around the prepolymerized powder particles to form hardened PMMA. In the process, heat is generated; this is called an “an exothermic reaction”. The polymerization process begins when the liquid, acrylic monomer wets the powder particles. As the powder dissolves, an “initiator” in the powder is released that activates some monomer molecules, which then attach to other monomer molecules, which, in turn, activates them. A chain is formed as the process continues, with the addition of more monomer material. The end result is a soft, pliable, doughy material, which then hardens into a cement-like PMMA complex. As each monomer is added, energy is expended in the form of heat; this palpable heat signals to the user that polymerization has occurred. Table 2 – Components of Bone Cement Powder Polymer Polymethylmethacrylate/copolymer (PMMA) Initiator Benzoyl peroxide (BPO)
Liquid Monomer Methylmethacrylate (MMA) Accelerator N, N-Dimethyl para-toluidine (DMPT) diMethyl para-toluidine (DMpt) Stabilizer Hydroquinone
Radio-opacifier Barium sulphate (BaSO4) Zirconia (ZrO2) Antibiotics (eg, gentamicin)
As previously noted, PMMA is a filler, not an adhesive, ie, it does not bond substances together; rather it acts like a mortar or grout to fill the void between the surface of the implant and the interstitial spaces in the surrounding cancellous bone (see Figure 1). Bone cement functions as a supportive material, that forms a mechanical bond between the cement and the bone and the cement and the prosthesis. In arthroplasty procedures, it forms a bond between the bone, the cement, and the prosthesis.14,15 When hardened, bone cement forms a buffer between the bone and the prosthesis that evenly distributes weight and other stresses that impinge on the prosthesis and bone.
Figure 1 – Bone Cement Penetration
↑ ↑ ↑ Bone Cement
Types of Bone Cement It is also important to note that there are several types of bone cement in regards to its viscosity. Viscosity affects the bone cement’s handling characteristics, handling time, and its penetration into the cancellous bone and therefore, the quality and longevity of the fixation achieved. Optimum viscosity helps cement penetrate the bone for good attachment, ie, the cement must be liquid enough to be delivered and then to penetrate the interstices of cancellous bone. Viscosity is defined as a measure of the resistance of a fluid to deformation under shear forces and it is commonly described as the “thickness” of a fluid.16 Viscosity also represents the resistance to flow and it is thought to be a measure of fluid friction. To some extent, solids may have viscous properties. Solid bodies, such as a cement mantle, which have elasticity and viscosity in a specific range of deformation and rate of deformation, are called viscoelastic. There are two requirements for bone cement viscosity during the working phase: first, viscosity must be sufficiently low to facilitate the delivery of the cement dough from the syringe to the bone site; secondly, it must penetrate into the interstices of the trabecular bone. On the other hand, the viscosity of the bone cement should be sufficiently high to withstand the back bleeding pressure, thereby avoiding the risk of the inclusion of blood into the cement. Blood inclusion 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. Low, medium and high viscosity cements are described below. ●●
Low viscosity cements – these cements remain in a runny state for a much longer period of time as compared to medium or high viscosity cements. Typically they have a long waiting phase. The true working time in which the cement can be picked up with a gloved hand usually is short, and the setting time can vary. Medium viscosity cements – these types of cements can offer versatility for various types of procedures. Medium viscosity cements are both low and high in viscosity, depending on the time at which the cement is delivered. Medium viscosity cements are considered to be dual phase cements. They begin in a low viscosity state while being mixed, which allows for the easy and homogenous mixing of the powder and the liquid. High viscosity cements – these types of cements primarily are comprised of PMMA with no methylmethacrylatestyrene-copolymer content; they have no runny state at all. Immediately after mixing, the cement is doughy and ready to apply by hand to the implant surface. The working time for high viscosity cements needs to be closely monitored; it is not always easy to determine the end of the working time before it is too stiff to interdigitate with the bone.
The American Society for Testing and Materials (ASTM) F451-08 Standard Specification for Acrylic Bone Cement also addresses the various types of bone cement.17 This standard covers self-curing resins which primarily are used for the fixation of internal orthopedic prostheses. While a variety of copolymers and comonomers may be incorporated, the composition of the set cement shall contain poly (methacrylic acid esters) as its main ingredient. The mixture may be used in either the predough or dough stages. The ASTM specification also addresses compositional, physical performance, and biocompatibility, as well as packaging requirements. Materials shall be tested and shall conform to specified values of appearance, stability, sterility, viscosity, intrusion, and compressive strength.
Indications for the Use of Bone Cement PMMA bone cement is intended for use in arthroplastic procedures of the hip, knee, and other joints for the fixation of polymer or metallic prosthetic implants to living bone.18 Other indications include: ●● Joint deterioration due to rheumatoid arthritis, osteoarthritis, or traumatic arthritis; ●●
Sickle cell anemia;
Severe joint destruction secondary to trauma or other conditions;
Revision of a previous arthroplasty; and
Fixation of pathological fractures where loss of bone substance or recalcitrance of the fracture renders more conventional procedures ineffective.
Factors that support the rationale for use includes aseptic loosening; unsuccessful results with uncemented femoral components; continuing improvements in cementing techniques; and the escalating cost of press-fit, porous coated hip and knee implants.
Contraindications to the Use of Bone Cement PMMA bone cement is contraindicated in the presence of active or incompletely treated infection, at the site where the bone cement is to be applied.19 The use of PMMA is also contraindication for patients who: ●●
Are pregnant or nursing;
Are allergic to the antibiotic or any of the other components of PMMA;
Have a history of hypersensitivity or serious toxic reactions to aminoglycosides, eg, gentamicin or vancomycin, due to the known cross-sensitivity of patients to drugs in this class. For example, there may be increased risk of ototoxicity from gentamicin, if drugs such as cisplatin and vancomycin are administered at the same time; Have an active infectious arthritis of the joint or joints to be replaced or a history of such an infection; Have a loss of musculature or have neuromuscular compromise in the affected limb, this would render the procedure unjustifiable;
Have myasthenia gravis;
Have metabolic disorders which may impair bone formation;
Are hypotensive; 8
Have renal impairment; and
Have congestive heart failure.
Selection Criteria The following are brief criteria for selection of both the patient as well as the appropriate type of bone cement for a specific surgical procedure.
Patient Selection Criteria
Key patient selection criteria related to the use of bone cement include the following factors: ●●
Activity level – the patient’s activity level, ie, is he or she relatively active or relatively sedentary? This will affect the selection of the type of bone cement to be used. Health status – the overall health status of the patient must be considered, as the bone cement induces a drop in blood pressure. Osteoporosis – bone density and disease must be assessed, as well as the presence of bone cysts and voids.
Bone Cement Selection Criteria Selection of the optimal bone cement for a specific clinical application depends on several variables, including its chemical composition and mechanical properties. ●●
Chemical composition – the primary determinant of the fatigue life of the various types of commercially available bone cements is their basic chemical composition. Variables such as powder (bead) size, molecular weight, and the addition of copolymers and radiopaque materials are important in determining the fatigue behavior of a particular type of bone cement. Each brand of bone cement has a slightly different composition. Mechanical properties – bone cement is evaluated for use based on the following five mechanical properties: o o o o o
Fatigue strength – this is a measure of the cement’s durability over time. It is an important factor, as patients are living longer and staying more active. Compressive strength – this measures the cement’s durability during weight bearing. Flexural strength – this is a measure of the cement’s ability to withstand bending stresses, such as those experienced while walking, climbing stairs, or rising from a chair. Impact strength – this is a measure of the cement’s ability to withstand sudden impacts, such as those which occur from a fall. Creep – creep measures the cement’s reaction to a combination of compressive and shear forces. These forces occur during a variety of normal activities of daily living over time. Creep, also known as plastic deformation, essentially is a mechanical problem that slowly and steadily can erode the longterm performance of an implant. As noted, bone cement is an acrylic, and it is similar to other plastics, in that it undergoes relaxation over time. All bone cements creep to some degree; however, cements with higher porosity and viscosity are less resistant to creep deformation.
PMMA Bone Cement Preparation In this section, the different components and formulations of bone cement, the phases of the polymerization process, the various types of bone cement, and the criteria for selecting the appropriate cement type will be reviewed. Processing and Handling of Bone Cement It is important that the personnel involved in the preparation and mixing of PMMA bone cement understand the handling characteristics and the setting times of the various types of cement. These factors directly impact surgery time and surgical outcomes. Once the liquid and powder components are mixed during the routine application of acrylic bone cement in a surgical procedure, the polymerization process is divided into four phases: mixing, waiting, working, and hardening. 20,21 ●●
Mixing phase – the mixing phase starts with the addition of the liquid to the powder and ends when the dough is homogenous and stirring becomes effortless. When the liquid and powder components of the cement are mixed together, the liquid wets the surface of the prepolymerized powder. Because PMMA is a polymer that dissolves in its monomer (which is not the case for all polymers), the prepolymerized beads swell and some of them dissolve completely during mixing. This dissolution results in a substantial increase in the viscosity of the mixture; however, at this stage the viscosity is still relatively low, compared with the later phases of polymerization. At the end of the mixing phase, the mixture is a homogenous mass and the cement is sticky and has a consistency similar to toothpaste. Waiting phase – the mixing phase is followed by a waiting period to allow further swelling of the beads and to permit polymerization to proceed. This leads to an increase in the viscosity of the mixture. During this phase, the cement turns into sticky dough. This dough is subsequently tested with gloved fingers every 5 seconds, using a different part of the glove on another part of the cement surface on each testing occasion. This process provides an indication of the end of the waiting phase when the cement is neither “sticky” nor “hairy”. Working phase – the beginning of the working phase occurs when the cement is no longer sticky, but is of sufficiently low viscosity to enable the surgeon to apply the cement. During this period, polymerization continues and the viscosity continues to increase; in addition, the reaction exotherm associated with polymerization leads to the generation of heat in the cement. In turn, this heat causes thermal expansion of the cement, while there is a competing volumetric shrinkage of the cement as the monomer converts to the denser polymer. During the working phase, the viscosity of the cement must be closely monitored because with a very low viscosity, the cement would not be able to withstand bleeding pressure. This would result in blood lamination in the cement, which causes the cement to weaken. This phase is completed when the cement does not join without folds during continuous kneading by hand; at this point, an implant can no longer be inserted (Figure 2). Therefore, the prosthesis must be implanted before the end of the working phase.
Figure 2 – Working Phase: Testing the Cement22
Hardening or setting phase – the last phase is the hardening or the setting period, in which the polymerization stops and the cement cures to a hard consistency. As noted, the prostheses must be in place prior to this phase. The 10
temperature of the cement continues to be elevated, but then slowly decreases to body temperature. During this phase, the cement continues to undergo both volumetric and thermal shrinkage as it cools to body temperature. The cement is ready for implantation when two cement balls are touched to each other and they stick together; if they do not stick together, the cement is in the curing stage and should not be used to implant the prosthesis. If implantation is completed with the cement in the curing stage, it could result in the cement delaminating or separating from the bone and/or the prosthesis. It is difficult to predict the hardening time with accuracy, due to the various factors in the OR which can alter the setting times of the cement. These factors include the ambient environment in the OR, the patient’s body temperature, and the thickness of the cement. In general, all bone cements define doughing, working, and setting time23: ●●
Dough time – starts from beginning of mixing and ends at the point when the cement will not stick to unpowdered surgical gloves. This occurs approximately 2-3 minutes after the beginning of mixing for most PMMA cements. Working time – this is the time from the end of dough time until the cement is too stiff to manipulate, usually about 5-8 minutes. Setting time – 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) and is the dough plus working times; usually about 8-10 minutes.
Factors that Affect Bone Cement Preparation When preparing PMMA bone cement, only the mixing phase is considered to be constant; the waiting, working, and hardening phases are dependent on several factors, as noted below.24,25 ●●
The ambient temperature – the higher the temperature, the shorter the phases; the colder the temperature, the longer the phases. Bone cement package inserts will provide specific information on the duration of each period relative to temperature. The mixing process – mixing cement too quickly or too aggressively can hasten the polymerization reaction; this will generate an increased amount of energy, resulting in a reduced setting time. In addition, the kneading process required for medium-viscosity cement preparation results in a somewhat faster setting time than when low-viscosity cement is used. In general, the lower the heat of polymerization, the longer the setting time, and the greater the heat of polymerization, the shorter the setting time. The type of cement – the various types of cement have different setting times. The powder to liquid ratio – each type of bone cement is packaged with the exact amounts of powder and liquid required to produce a consistent end product. If more liquid, or less powder, than required is used, setting time will be prolonged; on the other hand, if less liquid, or more powder is used, setting time will be shortened. It is important to follow the manufacturer’s guidelines for mixing cement in order to have a consistent end product.
Bone Cement Additives
In recent years, various substances and compounds have been added to PMMA bone cement in an effort to reduce the adverse effects of high heat from polymerization (such as tissue damage and necrosis) and to strengthen the bone cement once it has hardened. These additives include nanoparticles of magnesium oxide (MgO) and barium sulfate (BaSO4),26 as well as multi-walled carbon nanotubes to slow down setting time. Also nanoparticles of gold (Au) and porous pure titanium (pTi) are used to increase cement strength.27,28,29 Allergic reactions to bone cement additives are not uncommon.30
Antibiotic Bone Cement31,32
As previously noted, the first preblended bone cement containing an antibiotic (tobramycin) became available for sale in the United States in 2003. Information gathered from preclinical and clinical studies, as well as interviews with orthopedic surgeons and infectious disease specialists, led to the choice of tobramycin. While tobramycin is the antibiotic most frequently chosen by surgeons for mixing into bone cement in the US, formulations also are available with gentamicin. Several factors influence the choice of antibiotic to be added to the bone cement; the antibiotic must: ●●
Be able to withstand the exothermic temperature of polymerization;
Be available as a powder;
Have a low incidence of allergy; and
Be able to elute from the cement over an appropriate time period.
Several studies have demonstrated the efficacy of the use of antibiotic bone cement. An early study conducted by Sterling, et al prospectively investigated a consecutive series of ten patients undergoing a cemented primary total hip replacement (THR) for osteoarthritis in order to establish the elution characteristics of antibiotic (tobramycin) bone cement.33 There was a direct correlation between the amount of tobramycin bone cement which was implanted and the amount of tobramycin that was absorbed systemically; in addition, excellent local delivery was achieved with minimal systemic concentrations. The authors therefore concluded that tobramycin bone cement is an efficient and safe method for the delivery of antibiotics after THR. Subsequently, Block and Stubbs conducted a systematic review of the literature to evaluate studies on the use of antibiotic bone cement for reducing the risk of deep wound infection.34 This review included 22 articles which provided estimates of the prophylactic effectiveness of antibiotic cement. In reducing deep wound infection, the use of antibiotic cement consistently was superior to plain cement, similar to the use of systematic antibiotics, and independent and additive in effect when combined with other prophylactic measures. The collective results nearly unanimously favored the prophylactic use of antibiotic cement in primary arthoplasty procedures.
Other Additives to Promote Healing
As we have discussed, antibiotics commonly used as additives for PMMA bone cement include vancomycin, gentamycin, and meropenem, in addition to tobramycin. Also, successful non-antibiotic bactericides that have been used as bone cement additives include quaternary ammonium compounds such as benzalconium chloride and cetyl pyridinium chloride.35
PMMA Bone Cement: Mixing and Application Mixing Techniques
Ultimately, clinical goal for the appropriate preparation of bone cement is to utilize mixing and application techniques that minimize porosity and contamination. In addition, concerns over the hazards associated with bone cement have created the need to reduce exposure of the OR staff. In pursuit of this goal, significant evolution of modern cement mixing techniques has occurred since the introduction of bone cement used in arthroplasty. Now these techniques are designed to produce a better end product and also to reduce the levels of monomer exposure in the OR and to minimize contact with the cement. Bone cement mixing technique classifications are briefly described below.36 As always, with any cement mixing system, it is important to follow the manufacturer’s instructions for use. ●●
Bag or hand mixing – cement mixing techniques originally began as bag or hand mixing. In this method, the liquid was injected into a powder bag and mixed by kneading it into low viscosity cement. Open bowl mixing – the next mixing technique was open bowl mixing. The liquid and powder were poured together into a plastic or stainless bowl and then mixed with a spatula. This produced a cement of unpredictable quality, with high porosity, due to air-filled spaces between the particles; air trapped between lumps of mixing material just before the 12
mixture becomes liquid; and the air introduced by the stirring during hand spatulation. This method also exposed the OR staff to noxious fumes. The harmful effects of these fumes will be discussed in greater detail later. ●●
Closed bowl mixing (see Figure 3) – subsequently, the closed bowl technique was developed to reduce personnel exposure to the harmful, noxious PMMA fumes. This technique was the early paddle mixing system, which evacuated the fumes by connection to the standard wall suction.
Figure 3 – Closed Bowl Mixing System
Centrifugation after mixing – immediate centrifugation of the cement mixture after the mixing process reduces the size of any entrapped air bubbles and, therefore, the porosity of the bone cement by spinning the powder and liquid together. This reduction in porosity has been shown to increase the compressive strength and handling properties of centrifuged cement substantially when compared to manually mixed specimens. The steps for the centrifugation of bone cement are as follows: 1. Chill the liquid monomer to negate the shortening effect of centrifugation on setting time. 2. Mix the powder and the chilled liquid together. 3. Introduce the resulting low-viscosity cement mixture into a cement syringe. 4. Place the syringe in the centrifuge. 5. Spin at high speed for a short period of time.
Vacuum mixing (see Figure 4) – vacuum mixing was the next development for mixing bone cement. Today, most operating rooms mix bone cement under a partial vacuum, where the cement is mixed under ideal conditions. This results in a smaller amount of air becoming entrapped in the cement during mixing. Vacuum mixing systems may mix the cement in a cement syringe, in a bowl, or in a cement cartridge; the system remains closed up until cement delivery. All of these systems consist of an enclosed chamber connected to a vacuum source, such as wall suction or a dedicated vacuum pump; the vacuum source creates a partial vacuum during mixing. All ingredients are added and mixed while the system is closed.
Figure 4 – Vacuum Mixing System
With any type of vacuum mixing system, the components are added and mixed while the system is closed, following the same general procedure: 1. Wet the powder with the monomer. 2. Apply the vacuum while the mixing continues according to the manufacturer’s written instructions. The entrapped air bubbles will be drawn off via the partial vacuum, thus reducing the porosity and thereby increasing the fatigue strength of the cement. 3. The cement is then hand-packed or transferred to a cartridge with a spatula and a funnel. ●●
High vacuum mixing – the next development in the cement mixing process is high vacuum mixing. A pump is used to create an ideal vacuum of 20-22 millimeters of mercury. Paddle mixing is perfected in order to evacuate more air from the cement by utilizing an ideal surface area and ensuring inclusion of all powder and liquid. The combination of a closed vacuum system and carbon of a filter evacuates the harmful fumes. Also, this type of system allows for automatic transfer of cement into the cartridge while under vacuum. Cartridge mixing and delivery (see Figure 5) – the latest advancement in bone cement mixing technique is a simple, universal power mixer that quickly mixes and then mechanically injects all types of bone cement. This type of device reduces mix times, as it requires fewer steps to load, mix, and transfer the cement. The rotary hand piece reduces variability, which results in consistent mix times; a built-in charcoal filter reduces harmful fumes.
Figure 5 – Cartridge Cement Mixing and Delivery
The evolution of bone cement application techniques has paralleled that of mixing techniques. The methods for application of bone cement include: hand packing, injection, and gun pressurization; these are outlined below briefly.37,38 As with cement mixing devices, the manufacturer’s instructions for any cement delivery system should be followed. ●●
Hand packing – the original method of cement application was hand packing, where the femoral canal was packed either by the hand or finger. The proximal end was packed with cement by pressing with the fingers or thumbs; this pressurization forced the cement into the bone interstices. Commonly, in total knee arthroplasty, cementing is hand packed since the surfaces are readily visualized, which facilitates hand packing. Syringe injection – after hand packing, syringes are used to apply, or to inject, the cement. Syringes are the predecessors to today’s gun pressurization devices. Injection with hand pressurization – with hand pressurization, the proximal end is pressurized by pressing with the fingers or thumbs; this pressurization forces the cement into the bone interstices. 14
Injection with gun pressurization – the latest development in bone cement application methods is the gun pressurization device. Injection with gun pressurization offers a mechanical advantage that allows the surgeon to force more cement into the interstices at a greater rate of pressurization. Various pressurization tips allow more cement to be forced tightly into the bone, while preventing overflow.
Factors that Weaken Bone Cement39,40
Strict adherence to good cement application techniques is a key factor in reducing the rate of loosening and also in increasing the long-term survival of joint arthroplasty. But, there are factors that weaken bone cement that must be considered when mixing and applying bone cement. First, intrusion of foreign materials can weaken the cement. Often the word “contamination” is used to describe the presence of unwanted matter in bone cement; however, in the perioperative setting, typically the word “contamination” is associated with pathogenic invasion. Therefore, the word “intrusion” is better used in describing the effects that water, saline, blood, bone chips, or fat have on the setting time and the integrity of the hardened cement. Either a prolonged or a reduced setting time depends on the type and the volume of unwanted material that is introduced. Also, the presence of intrusion may cause laminations, which are faults or folds in the bone cement. Laminations create potential areas of weakness in the cement mantle where a failure can occur. Also, when the surgeon is trying to achieve a good interlock between cement, bone, and prosthesis they can create difficulties. The second factor that can affect the longevity of the attachment achieved by bone cement is the viscosity of the polymerizing mix at the time it is introduced into the bone. The cement’s viscosity affects its handling characteristics, its handling time, and its penetration of the cement into the cancellous bone. Optimum viscosity helps the cement penetrate the bone for good attachment of the prosthesis.
Safety Considerations for Patients and Healthcare Professionals Because the components of PMMA bone cement are toxic and highly flammable, all members of the perioperative team must be aware of the potential hazards associated with the use of PMMA for both personnel and patients in the OR environment. Appropriate safety precautions must be implemented to reduce the risk of exposure. Moreover, prior to using any type of PMMA bone cement, personnel should receive training about its properties, handling characteristics, mixing, and the application of bone cement.41 The specific hazards associated with bone cement and safety precautions are described below.
Potential Exposure Hazards ●●
Flammability42,43 – like many other materials used in the OR, methyl methacrylate is combustible, and it requires special measures to ensure safe handling. As packaged, bone cement does not pose a fire hazard; but, the liquid monomer is highly volatile and flammable with an open cup flash point of 50 degrees Fahrenheit. It is important never to bring a spark or other ignition source (eg, electrosurgery devices) near the surface of the liquid; therefore, proper storage of electrosurgical devices MUST be practiced to avoid potentially dangerous situations. While the product is considered stable, hazardous polymerization may occur and therefore, proximity to heat and ignition sources should be avoided; also it may polymerize on exposure to light. It is incompatible with oxidizing agents, peroxides, bases, acids, reducing agents, amines, halogens, and heat. Also, proper ventilation is an important factor in minimizing the danger of fire or explosion in confined spaces. In order to eliminate the maximum amount of monomer vapor, the OR should be adequately ventilated. The typical OR ventilation system is considered adequate for preventing a potentially hazardous build-up of monomer vapors. However, toxic gases and vapors, such as carbon monoxide, may be released in fires involving methylmethacrylate. In the unlikely event of a fire, the usual fire-fighting procedures are required. The fire can be extinguished with dry chemical, alcohol, polymer foam, or carbon dioxide extinguishers; water spray should be used to cool fire-exposed containers. Those fighting the fire should wear self-contained breathing apparatus and protective clothing to prevent contact with skin and eyes. Health hazards – potential health hazards are posed for OR personnel and patients when bone cement is used. These are described in detail below.
o Occupational hazards for OR staff – the adverse effects of liquid bone cement are the primary safety concerns when preparing and working with bone cement. Members of the surgical team are exposed to the monomer by skin contact and inhalation of vapors.44 The degree of potential hazard to the surgical team from the inhalation of the monomer vapor depends on its concentration level in the OR. The permissible exposure limit (PEL) value established by OSHA is a time-weighted average limit of 100 parts per million (ppm) of air or a time-weighted average of 410 milligrams per cubic meter of air during any 8-hour work shift in a 40-hour work week.45 -- Generally, methyl methacrylate is classified as an irritant. Excessive exposure to vapors can produce eye or respiratory tract irritation.46, 47 Exposure to high concentrations of the vapor may cause headache, dizziness, dyspnea, generalized erythroderma, and at very high levels, drowsiness and even loss of consciousness. Exposure to the liquid can cause considerable irritation or burns to the eyes; skin contact with the liquid monomer may produce irritation or burns. Allergic skin sensitization can also occur over time. Corneal ulcer has been reported to develop from exposure to the vapors. It may be metabolized in the liver to form a mutagenic substance. -- There are additional concerns regarding methyl methacrylate exposure for staff members who wear soft contact lenses. The manufacturers of soft contact lenses have recommended that these types of lenses be removed in the presence of noxious and irritating vapors. Soft contact lenses are very permeable and should not be worn in an OR where methyl methacrylate is being mixed, because the lenses are subject to pitting and penetration by the vapors. o Health hazards for patients – PMMA bone cement presents potential health hazards for patients as well. The adverse patient reactions to PMMA include transitory hypotension, cardiac arrest, cerebrovascular accident, pulmonary embolus, thrombophlebitis, and hypersensitivity reactions; while uncommon, cardiac arrest and death have occurred after application of bone cement.48 These adverse reactions have been attributed to several factors, including a rise in the intramedullary canal pressure, which causes embolic events; a possible chemical and blood reaction, causing sudden hypotension; and certain preexisting patient conditions. -- Bone cement implantation syndrome (BCIS) is a well-recognized complex of sudden physiologic changes that occur within minutes of the implantation of methyl methacrylate bone cement to secure a prosthetic component into the femur.49 For patients undergoing total hip arthroplasty with cemented implants, cardiopulmonary changes have contributed to intraoperative mortality ranging from 0.02% to 6.6% of the cases. Cardiac arrest and death are the most catastrophic symptoms associated with cemented arthroplasty. ●●
The underlying cause of the systemic hypotension and sudden cardiac failure is reported to be right ventricular failure secondary to increased pulmonary artery pressure (PAP). Serious embolization increases the PAP and pulmonary vascular resistance (PVR), causing the right ventricle to dilate; these changes reduce left ventricular filling and cardiac output. The resulting hypotension decreases coronary perfusion pressure. As right ventricular enddiastolic pressure increases, right coronary blood flow decreases, leading to low systemic blood pressure and creating ischemia of the right ventricle. This process produces a vicious cycle of right ventricular depression, failure, and death; as noted, these changes can occur within minutes of inserting a cemented prosthesis. Embolization is enhanced when tissue thromboplastin from the bone marrow is forced into the veins of the proximal femur during prosthetic insertion; this activates a clotting cascade, lesions of the venous endothelium, and thrombogenesis. Other theories about the cause of BCIS include: ▪▪ The direct effect of the exothermic reaction of cement temperature; ▪▪ Air or gas embolism caused by polymerization of methyl methacrylate monomer; ▪▪ Hypersensitivity/anaphylactic reaction to the acrylic monomer; 16
▪▪ Reflex bradycardia; ▪▪ Increase in intramedullary pressure resulting from the introduction of hot acrylic cement (this increase could force marrow and fat into the circulation, producing pulmonary emboli.); and ▪▪ Fat and debris from the femoral shaft embolize from the femoral canal during cement and implant insertion. o Factors that increase a patient’s risk for BCIS include: -- Elderly patients with underlying: ●●
Cardiovascular disease and who are undergoing cemented arthroplasty for repair of a fracture;
Severe osteoporosis; ●● Malignancies especially involving the femur; and ●● Pulmonary disease. -- Patients with intertrochanteric or pathologic fractures; and ●●
-- Patients who have pacemakers; who take sympathetic blockade medication; are hypotensive or have inadequate volume replacement; have a patent foramen ovale; are hemodynamically unstable at the time of cementing and prosthesis insertion; and have large femoral canals (eg, 21 mm or larger) requiring insertion of a long-stem femoral component. o Signs and symptoms of bone cement implantation syndrome may include one or more symptoms, including but not limited to: -- Hypotension; -- Pulmonary hypertension; -- Increased central venous pressure; -- Pulmonary edema; -- Bronchoconstriction; -- Anoxia or hypoxemia; -- Decreased partial end tidal carbon dioxide; -- Cardiac dysrhythmia or arrhythmia; -- Cardiogenic shock; -- Transient decrease in arterial oxygen tension; -- Hypothermia; -- Thrombocytopenia; -- Cardiac arrest; and -- Sudden death. o If the patient survives an initial episode, the syndrome is a time-limited phenomenon. The recovery time ranges from a few seconds to approximately 24 hours.50 The patient’s chance of survival is increased if the situation is immediately recognized and supportive measures are rapidly initiated (these measures will be described below). To facilitate the early recognition of bone cement implantation syndrome, the circulating nurse and the anesthesia provider should be familiar with the causes, risk factors, symptoms, and preventative interventions (as described below).51 17
Precautions to Minimize Excessive Exposure to PMMA in the OR Based on the potential hazards associated with the use of PMMA for patients and health care workers in the OR environment, personnel must implement appropriate safety precautions, as described below.
The potential hazards associated with the exposure of methyl methacrylate to any portion of the body in the perioperative practice setting should be identified and safe practices should be established to reduce the risk of injury to staff members and patients. Specific recommendations for the safe use of methyl methacrylate bone cement in the OR include52: ●●
Material safety data sheet (MSDS) information for methyl methacrylate 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. Methyl methacrylate should be handled according to its MSDS. Personnel should read and follow all instructions provided on the container label or found on the MSDS provided by the manufacturer of the chemical. Methyl methacrylate 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 reduce the fume levels to which users are exposed. Eye protection should be worn to prevent contact with eyes. As noted above, methyl methacrylate 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 methyl methacrylate and should be discarded after use. The manufacturer’s instructions should be followed regarding the composition of the second pair of gloves. Methyl methacrylate 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. Instead of hand mixing, a cement gun should be used to decrease handling of the product. The cement mixture should not be touched until it is the consistency of dough. Spills and disposal – the Environmental Protection Agency (EPA) classifies the liquid portion of bone cement as a hazardous substance; therefore, proper procedures are required for handling spills and disposal53, 54: o For methyl methacrylate 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. -- The waste product should be disposed of in a hazardous waste container. o Methyl methacrylate is considered hazardous waste and should be disposed of according to state, local, and federal regulations.
Measures to Reduce the Risk of BCIS55, 56
During the preoperative and preanesthetic assessments, the patient’s risk factors for BCIS, particularly the patient’s cardiopulmonary reserve, should be evaluated. This data should be used to select the prosthesis, the surgical procedure, and the techniques most likely to avoid cardiopulmonary complications. If necessary and medically feasible, delay the procedure until the patient’s medical and cardiovascular status can be maximized. Measures to reduce the risk of BCIS that may be implemented by the surgeon or anesthesia provider include, but are not limited to the following: ●● ●●
Using invasive hemodynamic monitoring when pre-existing cardiopulmonary problems exist and during cementing; Maintaining a high level of arterial oxygenation and increasing inspired oxygen concentration by administering 100% oxygen during the procedure;
Decreasing the concentration of a volatile agent (when using general anesthesia) prior to insertion of the prosthesis;
Maintaining normovolemia intraoperatively, especially at the time of cementing and insertion of the prosthesis;
Placing a venting hole into the femur, especially if using a long-stem prosthesis;
Avoiding bilateral hip replacements with cemented prostheses if cardiopulmonary dysfunction is present;
Using a noncemented prosthesis, especially if the patient’s mean arterial pressure decreases 20% to 30% below baseline during canal reaming or plugging; Performing thorough, pulsatile, high-pressure, high-volume lavage and brushing followed by drying of the intramedullary canal of the femoral shaft;
Using a cement restrictor combined with other methods to reduce intramedullary pressures;
Using a low viscosity cement;
Mixing the bone cement in a vacuum;
Working the cement before insertion to remove volatile vasodilator compounds;
Using a cement gun to apply the cement under sustained low pressure;
Using a retrograde cement gun technique for cement insertion;
Using a vacuum tube along the linea aspera to drain the proximal femur, which reduces high intramedullary pressure during cement and prosthesis insertion; and Introducing the prosthesis stem slowly into the cemented femoral canal, thereby reducing pressurization.
The surgeon or anesthesia provider implements most of these preventative measures; however, it is critical that the circulating nurse and all of the scrub personnel know the appropriate interventions. Understanding the techniques that may prevent bone cement implantation syndrome assists perioperative personnel in preparing for possible event-related changes in the patient’s condition, should they need to assist with these interventions. The US FDA requires hospitals and other user facilities to report deaths and serious injuries associated with the use of medical devices, including bone cements and bone void fillers.57 The health care organization’s procedures should be followed for mandatory reporting.
Additional Exposure Control Methods58 Additional exposure control methods include: ●●
Engineering controls – a local exhaust hood should be used to remove exhaust fumes from the area in which methyl methacrylate is being mixed. A tent hood may be used, unless mixing can be done in a separately ventilated area. Portable hoods are available for use in the OR.
Work practices – health care workers should be instructed to avoid touching contaminated hands or gloves to their eyes or mouths. Medical monitoring – pre-exposure data should be recorded for the skin and respiratory systems of workers who may be exposed to methyl methacrylate. Thereafter, periodic monitoring should emphasize the skin and respiratory systems.
Emergency First Aid Procedures
Emergency first aid procedures for exposure to PMMA bone cement include59: ●● In the event of an emergency, institute first aid procedures and send for first aid or medical assistance. ●●
Eye exposure – if methyl methacrylate gets into the eyes, immediately wash the eyes with large amounts of water, lifting both the upper and lower lids occasionally. Get medical attention as soon as possible. Contact lenses should not be worn when working with this chemical. Skin exposure – if the skin is exposed to methyl methacrylate, immediately flush the contaminated skin with water. If methyl methacrylate soaks through the clothing, remove the clothing immediately and flush the skin with water. Medical attention should be sought if the skin is irritated. Breathing – if a person breathes in large amounts of methyl methacrylate, he/she should be moved to fresh air immediately. If breathing has ceased, perform artificial respiration. Keep the affected person warm and at rest. Get medical attention as soon as possible. Properly trained individuals may assist the affected person by administering 100% oxygen. Swallowing – when methyl methacrylate has been swallowed, get medical attention immediately. If medical attention is not immediately available, induce vomiting in the affected person (if he/she is conscious) by having him/her touch the back of the throat with his/her finger or by giving him/her syrup of ipecac as directed on the package. Do not induce vomiting if the person is unconscious. Rescue – move the affected person from the hazardous environment. If the exposed person has been overcome, notify someone else and implement the established emergency rescue procedures. Personnel should understand the facility’s rescue procedures and know the locations of rescue equipment before the need arises.
Information Resources Numerous resources that provide additional information about the safe use of PMMA bone cement are available; these include: ●● Manufacturer’s Guidelines – the manufacturer’s guidelines should always be followed for the type of bone cement being used, as well as for the type of mixing and application system being used. ●●
OSHA Hazard Communication Standard.60 – the OSHA Toxic and Hazardous Substances, Hazard Communication Standard, or the “right to know” directive, states that employees must be informed of the hazards associated with all chemicals that are used in the work setting. Material Safety Data Sheet (see Figure 6) – as previously discussed, the MSDS for methyl methacrylate, provided by the manufacturer, must be readily accessible in the perioperative practice setting. The MSDS contains information on identification of the hazards, precautions or any special handling needed, signs and symptoms of toxic exposure, and first aid treatment for exposures. Staff members should read and follow all instructions provided on the MSDS.
Figure 6 – MSDS Label
Association of periOperative Registered Nurses (AORN) Recommended Practices for a Safe Care Environment of Care states that potential hazards associated with chemicals used in the practice setting should be identified and safe practices should be established for their use.61 Methyl methacrylate is identified as a potentially hazardous chemical in the perioperative practice setting.
Summary PMMA bone cement has been used in cemented arthroplasty procedures for over 50 years. Today, it remains an important component in achieving optimal patient outcomes. The quality of bone cement is determined by several factors, including the type of cement selected, the mixing and application processes, and its viscosity; therefore, its effectiveness is highly dependent upon the use of appropriate mixing and application techniques. Additionally, the use of bone cement in the perioperative environment is associated with certain hazards for both patients and personnel. In the OR, bone cement must be handled and prepared properly in order to maximize its clinical benefits and also to protect patients and members of the surgical team from its potential adverse effects. All members of the surgical team involved in the preparation and use of bone cement must understand the clinical considerations related to its proper use thoroughly, as well as the appropriate measures for safe handling and emergency procedures in cases of spills or exposure incidents. Education and training are critical factors in the preparation and safe use of PMMA bone cement; through this knowledge and skill, both positive patient outcomes and a safe perioperative environment of care can be achieved.
Glossary Accelerator A catalytic agent used to hasten a chemical reaction. Bone Cement Implantation Syndrome (BCIS) A grouping of symptoms that occurs within minutes after the implantation of methyl methacrylate cement into the femoral canal. Cancellous Bone Bone that has a reticular, spongy, or lattice-like structure. Colophony A translucent, brittle substance derived from the stumps or sap of various pine trees used in preparation of ointments and plasters. Compressive Strength The measure of bone cement’s durability during weight bearing. 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. Doughing Time The limited period of time in which to apply, ie, the cement should be applied while the mixture is still doughy. Erythroderma Abnormal redness of the entire surface of the skin. Exothermic Reaction A chemical reaction (ie, a process in which one or more substances are changed into others) accompanied by the production of heat. Fatigue Strength The measure of bone cement’s durability over time. Flexural Strength The measure of bone cement’s ability to withstand bending stresses, such as those experienced while walking, climbing stairs, or rising from a chair. Handling Time The difference between the doughing time and the time that the cement is set. High Viscosity Bone Cement Bone cement that is comprised primarily of PMMA with no methyl methacrylate-styrene-copolymer content; with this type of cement, a short waiting/sticky phase is followed by a long working phase. The viscosity remains constant until the end of the working phase. The hardening phase lasts between 1.5 and 2 minutes. Impact Strength The measure of bone cement’s ability to withstand sudden impacts, such as those which occur from a fall. Intrusion The effect that water, saline, blood, bone chips, or fat have on setting time and the integrity of the hardened cement. Laminations Faults or folds in bone cement. Linea Aspera A longitudinal ridge running down the posterior surface of the shaft of the femur that extends proximally into three ridges to which various muscles are attached. Low Viscosity Bone Cement Bone cement that has a long waiting phase of approximately 3 minutes; the viscosity rapidly increases during the working phase and the hardening phase is about 1 to 2 minutes long. Medium Viscosity Bone Cement Bone cement that has a long waiting phase of approximately 3 minutes, but during the working phase, the viscosity only increases slowly; hardening takes between 1.5 and 2.5 minutes. Mutagenic Substance An agent that induces a permanent change in the genetic material. Parts Per Million (ppm) 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. 22
Polymethylmethacrylate (PMMA) Porosity
Setting Time Viscosity
The bonding of two or more monomers (ie, simpler molecules) to form a polymer (ie, a compound). The polymerization process is an exothermic reaction, meaning it produces heat and is conversely affected by the application of heat. An acrylic cement-like substance used to secure prostheses to bone during orthopedic surgery. Exposure usually occurs during mixing, preparation, and in the operating room. The presence of entrapped air in bone cement, formed as a result of volatilization of the liquid component and mixing techniques. Centrifugation and vacuum mixing methods, and pressurized cement application can decrease the porosity of bone cement. The time elapsed from the moment the powder and liquid components are mixed until the cement is set. The measure of the resistance of a fluid to deformation under shear forces that is commonly described as “thickness” of a fluid; also viscosity represents the resistance to flow and it is thought to be a measure of fluid friction. The viscosity of bone cement affects its handling characteristics, its handling time, and its penetration of the cement into the cancellous bone. The time required for bone cement to attain the correct consistency for application to the bone once the ingredients of PMMA are mixed and kneaded.
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