Bone cement


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Bone cement

  3. 3. Year Development1870 Themistokles Gluck First surgeon to implant a total knee prosthesis made of ivory in Germany The stems were fixedwith cement mixed of plaster and colophony1930’s Otto Rohm Synthesized a group of thermoplastics, i.e., acrylic polymers These polymers replaced hard rubber as the base materials for dentures1950’s –1960’s 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 me- tallic femoral prosthesis; First to realize that PMMA could be used to fillthe medullary canal and to blend with the bone morphology
  4. 4. 1970’s U.S. FDA Approved bone cement for use in hip and knee prosthetic fixation Cement was the preferred technique for total joint fixation Cementless fixationtechniques were1980’s preferred1990’s -Present Hybrid systems are the preferred technique2003 U.S. FDA Cleared the firstantibiotic bone cement preparation
  5. 5. Table 2 – Components of BoneCement Powder Liquid Polymer Monomer Polymethylmethacrylate/copolymer (PMMA) Methylmethacrylate (MMA) Initiator Accelerator N, N-Dimethyl para-toluidine (DMPT) Benzoyl peroxide (BPO) diMethyl para-toluidine (DMpt) Radio-opacifier Stabilizer Barium sulphate (BaSO4) Hydroquinone Zirconia (ZrO2) Antibiotics (e.g., gentamicin)
  6. 6. Types of Bone Cement : •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 methylmethacrylate-styrene-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.
  7. 7. INDICATIONS FORTHE USE OF BONE CEMENT : PMMA bone cement is intended for use in arthroplastic procedures of the hip, knee, and other joints for the fixationof polymer or metallic prosthetic implants to living bone. Other indications include: •Joint deterioration due to rheumatoid arthritis, osteoarthritis, or traumatic arthritis •Avascular necrosis •Sickle cell anemia •Collagen disease •Severe joint destruction secondary to trauma or other conditions •Revision of a previous arthroplasty •Fixation of pathological fractures where loss of bone substance or recalcitrance of the fracture renders more conventional procedures ineffective
  8. 8. CONTRAINDICATIONSTO 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.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 e.g., gentamicin or vancomycin, due to the known cross-sensitivity of patients to drugs in this class.•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•Have renal impairment•Have congestive heart failure
  9. 9. Processing and Handlingof Bone Cement : 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: 1 )mixing 2) Waiting 3)Working and 4)hardening
  10. 10. 1 ) Mixing Phase.The mixing phase starts with the addition of the liquid to the powderand ends when the dough is homogenous and stirring becomeseffortless.When the liquid and powder components of the cement are mixedtogether, the liquid wets the surface of the prepolymerized powder.Because PMMA is a polymer that dissolves in its monomer (which is notthe case for all polymers), the prepolymerized beads swell and some of them dissolvecompletely during mixing. This dissolution results in a substantialincrease in the viscosity of the mixture; however, at this stage theviscosity is still relatively low, compared with the later phases ofpolymerization. At the end of the mixing phase, the mixture is ahomogenous mass and the cement is sticky and has a consistencysimilar to toothpaste.
  11. 11. 2 ) Waiting Phase.The mixing phase is followed by a waiting period toallow further swelling of the beads and to permitpolymerization to proceed. This leads to an increase inthe viscosity of the mixture. During this phase, the cement turns into sticky dough. This dough is subsequently tested with gloved fingersevery 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.”
  12. 12. 3 ) Working Phase.The beginning of the working phase occurs when the cement is no longer sticky, but isof sufficiently low viscosity to enable the surgeon to apply the cement. During thisperiod, polymerization continues and the viscosity continues to increase; in addition,the reaction exotherm associated with polymerization leads to the generation of heatin the cement. In turn, this heat causes thermal expansion of the cement, while thereis a competing volumetric shrinkage of the cement as the monomer converts to thedenser polymer. During the working phase, the viscosity of the cement must be closelymonitored because with a very low viscosity, the cement would not be able towithstandbleeding pressure. This would result in blood lamination in the cement, which causesthe cement to weaken. This phase is completed when the cement does not joinwithout folds during continuous kneading by hand; at this point, an implant can nolonger be inserted (Figure ). Therefore, the prosthesis must be implanted before theend of the working phase.
  13. 13. Working Phase: Testing the Cement
  14. 14. 4) Hardening or Setting phase. The last phase is the hardening or the setting period, inwhich the polymerization stops and the cement cures to ahard consistency. As noted, the prostheses must be inplace prior to this phase. The temperature of the cementcontinues to be elevated, but then slowly decreases tobody temperature. During this phase, the cementcontinues to undergo both volumetric and thermalshrinkage as it cools to body temperature. The cement isready for implantation when two cement balls aretouched to each other and they stick together; if they donot stick together, the cement is in the curing stage andshould not be used to implant the prosthesis. Ifimplantation is completed with the cement in the curingstage, it could result in the cement delaminating orseparating from the bone and/or the prosthesis.
  15. 15. In general, all bone cements have definatedoughing, working, and setting time:•Dough time:starts from beginning of mixing and ends at the point when the cement willnot stick to unpowdered surgical gloves.This occurs approximately 2-3 minutes after the beginning of mixing for mostPMMA cements.•Working time:this is the time from the end of dough time until the cement is too stiff tomanipulate, usually about 5-8 minutes.•Setting time: from the beginning of mixing until the time at which the exothermic reactionheats the cement to a temperature that is exactly halfway between the ambient and maximum temperature (i.e., 50% of its maximum value) and is the dough + working times; usuallyabout 8-10 minutes.
  16. 16. Factors that AffectBone 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.•The ambient temperature. The higher the temperature, the shorter the phases;the colder the temperature, the longer the phases.•The mixing process. Mixing cement too quickly or too aggressively can hasten the polymerization reaction;this will generate an increased amount of energy 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.
  17. 17. Bone Cement Additives These additives include nanoparticles of magnesium oxide (MgO) and barium sulfate (BaSO4) 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. Antibiotic : 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.
  18. 18. antibiotics commonly used asadditives for PMMA bone cementinclude vancomycin, gentamycin,and meropenem, in addition totobramycin. Also, successful non-antibiotic bactericides that havebeen used as bone ce-mentadditives include quaternaryammonium compounds such asbenzalconium chloride and cetylpyridinium chloride.35
  19. 19. Mixing Techniques :Bone cement mixing technique classifications are briefly described below.As always, with any cement mixing system, it is important to followthe manufacturer’s instructions for use.•Bag or hand mixing. Cement mixing techniques originally began as bag or hand mixingn this method, the liquid was injected into a powder bag andmixed 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 stainlessbowl and then mixed with a spatula. This produced a cement of unpredictable quality, with high porosity,due to air-filledspaces between the particles;air trapped between lumps of mixing material just before the 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 ). Subsequently, the closed bowl technique was developed to reduce personnel exposure to the harmfulnoxious PMMA fumes. This technique was the early paddle mixing system,which evacuated the fumes by connection to the standard wall suction.
  20. 20. Centrifugation after mixing. Immediate centrifugation of thecement mixture after the mixing process reduces the size of any entrappedair bubbles and, therefore, the porosity of the bone cement by spinning thepowder and liquid together. This reduction in porosity has been shown toincrease 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: ●Chill the liquid monomer to negate the shortening effect of centrifugation on setting time. ●Mix the powder and the chilled liquid together. ●Introduce the resulting low-viscosity cement mixture into a cement syringe. ●Place the syringe in the centrifuge. ●Spin at high speed for a short period of time.
  21. 21. •Vacuum mixing (see Figure) Vacuum mixing wasthe 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 cementdelivery. 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.
  22. 22. With any type of vacuum mixing system,the components are added and mixed while the system is closed,following the same general procedure: ●Wet the powder with the monomer. ●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. ●The cement is then hand-packed or transferred to a cartridge with a spatula and a funnel.
  23. 23. •High vacuum mixing. The next development in the cementmixing 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 airfrom the cement by utilizing an ideal surface area andensuring inclusion of all powder and liquid.The combination of a closed vacuum system andcarbon of a filterevacuates the harmful fumes.Also, this type of system allows forautomatic transfer of cement into the cartridge while under vacuum.•Cartridge mixing and delivery (see Figure ).The latest advancement in bone cement mixing technique is a simple,universal power mixer that quickly mixes and then mechanically injectsall 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 filterreduces harmful fumes.
  24. 24. Figure –Cartridge Cement Mixing and Delivery
  25. 25. Application Techniques :The methods for applicationof bone cement include: hand packing, injection, and gun pressurization; these are outlined below briefly•Hand packing. The original method of cement application was hand packing, where the femoral canal was packed either by the hand or fingerThe. proximal end was packed with cement by pressing with the fingersor 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 fingersor thumbs;this pressurization forces the cement into the bone interstices.•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.
  26. 26. Factors that Weaken Bone Cement :• First, intrusion of foreign materials can weaken the cement.Often the word “contamination” is used to describe the presenceof unwanted matter in bone cement; however, in theperioperative setting, typically the word “contamination” isassociated 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 theintegrity of the hardened cement. Either a prolonged or areduced setting time depends on the type and the volume ofunwanted material that is introduced• The second factor that can affect the longevity of theattachment achieved by bone cement is the viscosity of thepolymerizing mix at the time it is introduced into the bone. • Optimum viscosity helps the cement penetrate the bone for good attachment of the prosthesis.
  27. 27. The specific hazards associated withbone cement andsafety precautions are described below : Health Hazards 1 ) Occupational hazards for surgical team OR staff : • Excessive exposure to vapors can produce eye or respiratory tract irritation • 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. • Soft contact lenses are very permeable and should not be worn where methyl methacrylate is being mixed, because the lenses are subject to pitting and penetration by the vapors.
  28. 28. 2 ) Health hazards for patients :transitory hypotension,cardiac arrest,cerebrovascular accident,pulmonary embolus,thrombophlebitis, and hypersensitivity reactions; while uncommon, cardiac arrestand death have occurred after application of bone cementBone cement implantation syndrome (BCIS) is a well-recognized complex ofsudden physiologic changes that occur within minutes of the implantationof methyl methacrylate bone cement to secure a prosthetic component into the bone
  29. 29. Signs and symptoms ofbone cement implantation syndromemay 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• sudden death
  30. 30. Factors that increase a patient’s risk for BCIS include: ● Elderly patients with underlying:• cardiovascular disease and who are undergoing cemented arthroplasty for re-pair of a fracture• severe osteoporosis• malignancies especially involving the femur• pulmonary disease• Patients with intertrochanteric or pathologic fractures• 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 (e.g., mm or larger) requiring insertion of a long-stem femoral component
  31. 31. Measures to Reduce the Risk of BCIS :• using invasive hemodynamic monitoring when pre-existing cardiopulmonary problems exist and during cementing• maintaining a high level of arterial oxygenation and increasing inspired oxygen concentrationby 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
  32. 32. • 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 introducing the prosthesis stem slowly into the cemented femoral canal, thereby reducing pressurization
  33. 33. Emergency First Aid Procedures :Emergency firstaid procedures for exposure to PMMA bone cement include:59•In the event of an emergency, institute firstaid procedures andsend for firstaid 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 flushthe contaminated skin with water. If methyl methacrylate soaks through the clothing,remove the clothing immediately and flushthe 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 artificialrespiration. 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.
  34. 34. • Swallowing – when methyl methacrylate has been swallowed, get medicalattention 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 fingeror 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.
  35. 35. THANK YOU