Effect of cement pressure and bone strength on polymethylmethacrylate fixation

The effect of the quality of the bone and of the cement pressurization magnitude and duration on the fixation achieved with polymethylmethacrylate (PMMA) bone cement is studied in vitro. Seventy-one cementbone interface specimens, prepared under various conditions of pressurization of low-viscosity bone cement, are tested in tension. The load at failure and the maximum cement penetration are measured to assess the fixation achieved, and the quality of the bone is assessed by determining the compressive strength of each of the bone specimens. Statistical analysis of the data indicates that the pressure magnitude is the most influential of the factors considered in the cement penetration behavior and in the development of failure load capacity. The duration of the pressure does not appear to be a significant factor. The cement penetration is a decreasing function of the bone strength, reflecting a decrease in the porosity and an increase in the area fraction. Although not directly measured in these tests, these latter bone properties are indirectly measured by the bone compressive strength. The effect of increasing bone strength on the failure load is nonlinear. The development of adequate failure load capacity is the result of a balance between the cement penetration allowed by the porosity of the bone and the inherent strength of the cancellous bone itself. Weak bone, although adequately penetrated by cement, cannot provide strong fixation. Stronger, denser bone limits cement penetration, but pressurization enhances development of failure load capacity through more complete infusion and interlocking of the cement in the available pore space. The strength of the fixation achievable for any bone is limited by the intrinsic strength of the bone. An optimal depth of cement penetration of 4 mm and an optimal bone area fraction of 0.20 are suggested for the most effective fixation.     

Effects of mixing techniques on vancomycin-impregnated polymethylmethacrylate

The use of antibiotic-impregnated polymethylmethacrylate in joint arthroplasty is widespread. The Food and Drug Administration has approved commercially prepared antibiotic bone cement, but in a climate of increasingly drug-resistant bacteria, orthopedic surgeons often hand-mix their own. A recent study reported the effects on drug elution of different mixing methods designed to decrease antibiotic particle size and distribute those particles more uniformly. Theoretically, these mixing techniques could also improve antibiotic cement strength; however, the actual effects of these techniques on cement strength are undefined. In the present study, 3 different methods of mixing vancomycin with bone cement were compared. We conclude that the addition of vancomycin to polymethylmethacrylate at commonly accepted concentrations does substantially decrease cement strength and that more complex mixing techniques do not improve cement strength significantly.     

Prechilling and vacuum mixing not suitable for all bone cements: Handling characteristics and exotherms of bone cements

Nine bone cements were tested for handling characteristics, intrusion, doughing time, setting time, and exothermic temperature. Comparative studies were made of manual mixing and vacuum mixing of cement components stored at room temperature or chilled to 5 degrees C. Vacuum mixing of cement packages stored at room temperature was inapplicable except for the low-viscosity brands, as the cements became too viscous to mold test specimens. Prechilling and vacuum mixing prolonged the setting time and preserved a lower viscosity during the handling period. Palacos R and Palacos G were most suitable for this method, whereas a considerable increase in exothermic temperature was experienced with the other brands. The method might, however, be considered for Zimmer and Cerafix also, as the exotherm was of the same magnitude as for Palacos brands.     

Response of fractured osteoporotic bone to polymethylmethacrylate after vertebroplasty: case report

BACKGROUND CONTEXT: Polymethylmethacrylate (PMMA) is the most commonly used bone cement for vertebroplasties to treat osteoporotic vertebral compression fractures (VCFs). Several studies have described the reaction of normal bone to PMMA, but it is still unclear how fractured osteoporotic bone responds to PMMA. PURPOSE: To describe the response of fractured osteoporotic bone to PMMA after vertebroplasty. STUDY DESIGN/SETTING: Case report. METHODS: A 69-year-old woman with a previous vertebroplasty at T8 to treat an osteoporotic VCF was admitted to the hospital after she developed lower extremity motor weakness, diffuse hypoesthesia and decreased rectal tone. Magnetic resonance imaging studies of the thoracic spine showed that she had severe spinal cord compression at the level of T8 and T9, as well as akyphotic deformity. A corpectomy of T8 and T9 was performed as part of a spinal cord decompression procedure. Tissue from vertebral body T8, intervertebral discs T7-T8 and T8-T9 and the PMMA implant were then submitted for histologic evaluation.RESULTS: Vertebral body T8 demonstrated viable bone trabeculae, osteoid. fibrosis, granulation tissue and multinucleated giant cells containing PMMA. Scattered necrotic bone fragments were identified throughout the vertebral body, most evident near the PMMA. PMMA leakage into the T7-T8 disc was identified without significant disc inflammation or necrosis. CONCLUSION: Fractured osteoporotic bone is capable of undergoing a reparative healing response after vertebroplasty using PMMA.     

Antibiotic-free antimicrobial poly (methyl methacrylate) bone cements: A state-of-the-art review

Prosthetic joint infection (PJI) is the most serious complication following total joint arthroplasty, this being because it is associated with, among other things, high morbidity and low quality of life, is difficult to prevent, and is very challenging to treat/manage. The many shortcomings of antibiotic-loaded poly (methyl methacrylate) (PMMA) bone cement (ALBC) as an agent for preventing and treating/ managing PJI are well-known. One is that microorganisms responsible for most PJI cases, such as methicillin-resistant S. aureus, have developed or are developing resistance to gentamicin sulfate, which is the antibiotic in the vast majority of approved ALBC brands. This has led to many research efforts to develop cements that do not contain gentamicin (or, for that matter, any antibiotic) but demonstrate excellent antimicrobial efficacy. There is a sizeable body of literature on these so-called “antibiotic-free antimicrobial” PMMA bone cements (AFAMBCs). The present work is a comprehensive and critical review of this body. In addition to summaries of key trends in results of characterization studies of AFAMBCs, the attractive features and shortcomings of the literature are highlighted. Shortcomings provide motivation for future work, with some ideas being formulation of a new generation of AFAMBCs by, example, adding a nanostructured material and/or an extract from a natural product to the powder and/or liquid of the basis cement, respectively.     

The effect of intramedullary polymethylmethacrylate on healing of intercalary cortical allografts in a canine model.

The purpose of this study was to evaluate the effect of intramedullary polymethylmethacrylate (PMMA) bone cement on the healing of intercalary allografts. Thirteen adult beagles had bilateral intercalary femoral allografts implanted. The medullary canal of one randomly assigned allograft in each dog was filled with PMMA. Healing was followed clinically and femora were evaluated radiographically, biomechanically, histologically, and histomorphometrically 9 months after surgery. There was an increased percent of eroded surface at the endosteal area of the center region of grafts containing PMMA and there was an increased percent osteoblast surface in this area in grafts not containing PMMA. There was an increased percent eroded surface at the periosteal area in the center region in grafts not containing PMMA and there was an increased percent osteoblast surface at the periosteal area in the graft adjacent to the host junction in grafts containing PMMA. There was no significant difference between PMMA-treated and untreated allografts in any other parameters measured. The results from this study suggest that, although the pattern of incorporation is altered, intramedullary PMMA does not appear to effect allograft healing adversely.     

Polymethylmethacrylate bone cements and additives: A review of the literature

Polymethylmethacrylate (PMMA) bone cement technology has progressed from industrial Plexiglass administration in the 1950s to the recent advent of nanoparticle additives. Additives have been trialed to address problems with modern bone cements such as the loosening of prosthesis, high post-operative infection rates, and inflammatory reduction in interface integrity. This review aims to assess current additives used in PMMA bone cements and offer an insight regarding future directions for this biomaterial. Low index (< 15%) vitamin E and low index (< 5 g) antibiotic impregnated additives significantly address infection and inflammatory problems, with only modest reductions in mechanical strength. Chitosan (15% w/w PMMA) and silver (1% w/w PMMA) nanoparticles have strong antibacterial activity with no significant reduction in mechanical strength. Future work on PMMA bone cements should focus on trialing combinations of these additives as this may enhance favourable properties.     

The compressive properties of bone cements containing large doses of antibiotics

The addition of large amounts of antibiotics to bone cement provides a convenient local delivery, but may influence the compressive properties of the cement. Flucloxacillin and vancomycin were added to Simplex P (Stryker, Limerick, Ireland) and VersaBond (Smith & Nephew) cements. Tripling the antibiotic dose from 2 to 6 g had little effect on the static compressive properties 24 hours after curing. After 4 weeks in phosphate-buffered saline, there was marked decrease in properties with the addition of antibiotics. Compressive strength of cements with 6 g of antibiotic was reduced to near or below the ASTM and ISO minimum of 70 MPa after 4 weeks in phosphate-buffered saline. Microcomputer tomography revealed increased porosity and clumping of the radiopacifier with the addition of antibiotics.     

松质骨螺钉骨水泥强化的生物力学和组织学研究

目的通过动物实验观察不同骨水泥强化松质骨螺钉的生物力学和组织学变化动态,为骨质疏松骨折患者内固定提供理论基础。方法在10只杂种犬胫骨近端制作松质骨螺钉植入的动物模型,分别采用碳酸化羟基磷灰石水泥(CHC)和聚甲基丙烯酸甲酯(PMMA)强化,分别于术后5d、4、8、12和16周处死动物,观察螺钉拔出的生物力学和组织学变化。结果CHC强化的螺钉拔出力随手术后时间的延长而逐渐升高,16周时达到(512.5 14.5)N,而PMMA强化组螺钉拔出力则随手术后时间的延长而逐渐降低。CHC-骨界面结合紧密,并且随时间延长出现CHC降解和骨长入,而PMMA-骨界面形成一层纤维组织。结论CHC强化能够提高松质骨螺钉植入体内的稳定性,并且随植入时间延长而逐渐升高。     

多孔载因子CPC促进骨缺损愈合的实验研究

[目的]探讨磷酸钙骨水泥复合rhBMP-2/明胶微球复合材料在治疗骨缺损时的降解、成骨性能。[方法]制备携载rhBMP-2的明胶微球(GMs),与磷酸钙骨水泥(CPC)复合,制备出rhBMP-2/GMs/CPC复合人工骨。取30只新西兰大白兔,在前臂桡骨中段制造人工骨缺损,随机分成3组,分别植入rhBMP-2/GMs/CPC/复合物(A组)、GMs/CPC(B组)、rhBMP-2/CPC(C组),术后6、12周分别进行X线检测、骨密度测定,术后12周处死动物,分别行生物力学测定,脱钙切片、HE染色,不脱钙切片进行荧光显微镜下观察双标间距,计算平均矿化率。[结果]与GMs/CPC、rhBMP-2/CPC组比较,复合材料植入后不同时间点的材料降解及成骨均高于对照组。12周A组标本生物力学实验测定结果表明指标接近正常,与B、C组比较有统计学差异。骨密度12周、新骨矿化率提示有统计学差异。[结论]rhBMP-2/GMs/CPC微球系统复合材料在体内易降解,具有良好成骨活性,是良好的骨修复材料。     

An articulated antibiotic spacer used for infected total knee arthroplasty: a comparative in vitro elution study of Simplex and Palacos bone cements.

For the staged management of infected total knee arthroplasty (TKA), antibiotic laden polymethylmethacrylate (PMMA) spacers have been recommended. Antibiotic-impregnated PMMA spacers target drug delivery, achieving high local levels while limiting the potential for host toxicity associated with parenteral antimicrobial therapy. This study examined the elution characteristics of an articulating PMMA TKA spacer that has been useful clinically. Tobramycin and vancomycin are both active against many organisms leading to joint infections. We used various combined antibiotic concentrations (maintaining a relative ratio of 55% tobramycin to 45% vancomycin w/w), and then assayed the elution profile of the TKA spacer in vitro. Additionally, the elution qualities of two brands of bone cement, Simplex and Palacos, were compared. Briefly, three groups of PMMA spacers, impregnated with different antibiotic loads, were fashioned from a mold replicating a femoral TKA component. The entire spacer surface area was immersed in sterile phosphate buffered saline (PBS) in a 1:6 ratio of grams of cement to milliliters of PBS and incubated at 37 degrees C for 24 h. After 24 h, aliquot eluates were taken, the PBS discarded, and replaced with fresh, sterile PBS. PBS was changed daily and an aliquot was taken at least weekly for nine weeks. Eluate samples were stored at -70 degrees C until assayed. Each spacer eluate sample's antibiotic concentration was determined by disc diffusion bioassay against Bacillus subtilis. Mean zone inhibition diameters were extrapolated from the standard curve to yield micrograms per milliliter of antibiotic in PBS. In all groups the Palacos spacers demonstrated higher elution levels, above the MIC for the organism used, for a longer period of time than those made with Simplex. Based on the observed elution profiles, antibiotic-impregnated Palacos bone cement may offer a more effective vehicle for local drug delivery during staged treatment of infected TKA.     

Finite element simulation of cement‐bone interface micromechanics: A comparison to experimental results

Recently, experiments were performed to determine the micromechanical behavior of the cement‐bone interface under tension‐compression loading conditions. These experiments were simulated using finite element analysis (FEA) to test whether the micromechanical response of the interface could be captured in micromodels. Models were created of experimental specimens based upon microcomputed tomography data, including the complex interdigitated bone‐cement morphology and simulated frictional contact at the interface. The models were subjected to a fully reversed tension‐compression load, mimicking the experimental protocol. Similar to what was found experimentally, the simulated interface was stiffer in compression than in tension, and the majority of displacement was localized to the cement‐bone interface. A weak correlation was found between the FEA‐predicted stiffness and the stiffness found experimentally, with average errors of 8 and 30% in tension and compression, respectively. The hysteresis behavior found experimentally was partially reproduced in the simulation by including friction at the cement‐bone interface. Furthermore, stress analysis suggested that cement was more at risk of fatigue failure than bone, concurring with the experimental observation that more cracks were formed in the cement than in the bone. The current study provides information that may help explain the load transfer mechanisms taking place at the cement‐bone interface. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1312–1318, 2009     

Ablation of polymethylmethacrylate by Ho:YAG,Nd:YAG,and Erb:YAG lasers

Ho:YAG, Nd:YAG, and Erb:YAG laser ablation of Polymethylmethacrylate (PMMA) was investigated under in vitro and simulated clinical conditions. Ablation rates were measured for all lasers and after ablation, macroscopic and microscopic appearance of the ablation site was investigated. The mean ablation rates of the Erb:YAG, Ho:YAG, and Nd:YAG laser increased from 8 μm per pulse at 100 mJ to 44 μm per pulse at 300 mJ from 100 μm per pulse at 200 mJ to 222 μm per pulse at 800 mJ and from 28 μm per pulse at 100 mJ to 189 μm per pulse at 800 mJ, respectively. Macroscopic investigation exhibited melting of bone cement for the Ho:YAG and Nd:YAG lasers and pulse-to-pulse vaporization for the Erb:YAG laser. The width of thermal alteration, however, was comparable for all lasers used. Removal of cement from bone specimens under simulated clinical conditions showed good detachment of cement when the fiber was used parallel; in case of perpendicular use, remainders of cement and carbonization of bone could be observed upon histological investigation. © 1993 Wiley-Liss, Inc.     

三种骨水泥应用于椎体成形术的生物力学比较

目的:评价硫酸钙(CSC)、磷酸钙(CPC)与聚甲基丙烯酸酯(PMMA)3种骨水泥用于椎体成形术的生物力学性能。方法:将16具小牛胸腰段(T11～L1)标本分为4组,A、B、C组制成T12爆裂骨折模型,D组为无骨折对照组,测量爆裂骨折前、后和复位并分别注射CSC(A组)、CPC(B组)、PMMA(C组)行椎体成形术后椎体前缘高度,达到骨水泥完全填充时的骨水泥注射量;生物力学检测4组标本的极限抗压强度及刚度。结果:12具标本均形成胸腰椎爆裂骨折模型,平均撞击能量66.2J;CSC、CPC、PMMA注射量分别为4.35±0.80ml、3.72±0.73ml及3.95±0.63ml,3组间无显著性差异(P>0.05);3种骨水泥均能有效充填爆裂椎体复位后残留的骨缺损及恢复伤椎高度(P<0.01);A、B、C及D组的极限抗压强度分别为1659±154N、1011±142N、2821±897N及2439±525N,C组能完全恢复椎体的抗压强度,A、B组可部分恢复,但A组优于B组(P<0.01);4组标本的刚度分别为140±40N/mm、148±33N/mm、236±97N/mm及224±38N/mm,A组刚度低于D组(68.0%,P<0.05),但与B、C组无显著性差异(P>0.05)。结论:3种不同成分骨水泥中,PMMA的强度最高,CSC次之,CPC的强度最差,刚度方面三者间无明显差别;CSC用于椎体成形术能满足对椎体填充材料的生物力学要求,可作为椎体成形术中填充材料的选择之一。     

Fenestrated pedicle screws for cement-augmented purchase in patients with bone softening: a review of 21 cases

Background  

This prospective mixed cohort study was designed to evaluate the middle- to long-term purchase of cement-augmented pedicular screws in patients with poor bone quality. The growing number of surgical procedures performed in the spine has highlighted the problem of screws loosening in patients with poor bone stock due to osteoporosis and/or tumors. Different methods of increasing screw purchase have been reported in the literature, including polymethylmethacrylate (PMMA) augmentation.     

Antimicrobial efficacy of gentamicin-loaded acrylic bone cements with fusidic acid or clindamycin added.

The increasing gentamicin resistance among bacteria in septic joint arthroplasty has stimulated interest in adding a second antibiotic into gentamicin-loaded bone cement. A first aim of this in vitro study is to investigate whether addition of fusidic acid or clindamycin to gentamicin-loaded bone cement has an additional antimicrobial effect against a collection of 38 clinical isolates, including 16 gentamicin-resistant strains. A modified Kirby-Bauer test, involving measurement of the inhibition zone around antibiotic-loaded bone cement discs on agar plates, was used to investigate whether adding a second antibiotic has an additional antimicrobial effect. Second, a selected number of strains was used to study their survival in an interfacial gap made in the different bone cements to mimic the gap between bone and cement as existing near a prosthesis. Gentamicin-loaded bone cement had an antimicrobial activity against 58% of the 38 bacterial strains included in this study, while 68% of the strains were affected by bone cement loaded with a combination of gentamicin and clindamycin. Bone cement loaded with the combination of gentamicin and fusidic acid had antimicrobial activity against 87% of the bacterial strains. In the prosthesis-related gap model, there was a clear trend toward less bacterial survival for gentamicin-loaded bone cement after adding clindamycin or fusidic acid. Addition of clindamycin or fusidic acid into gentamicin-loaded bone cement yields an additional antimicrobial effect. The combination gentamicin and fusidic acid was effective against a higher number of clinical isolates than the combination of gentamicin with clindamycin, including gentamicin-resistant strains.     

An in vitro comparison of tibial tray cementation using gun pressurization or pulsed lavage

Purpose

Aseptic loosening of the tibial component remains a limitation to the highly successful procedure of total knee arthroplasty (TKA). Pulsed lavage improves bone cement penetration and interface strength in tibial tray cementation. This study tested whether pressurized cement application with a cement gun can compensate the use of jet lavage for bone surface preparation.

Methods

Tibial components were implanted in six pairs of cadaveric tibiae. On one side, pulsed lavage of the tibial bone was combined with finger packing of bone cement; on the other side, syringe lavage and gun cementing was used. Cement penetration into the bone was determined from computed tomography scans, and Interface strength was determined by pull-out testing.

Results

Cement penetration was greater (p = 0.004) and interface strength was higher (p = 0.028) in the pulsed lavage group.

Conclusion

Pressurization of cement by gun application could not compensate for the omission of pulsed lavage. Thus, pulsed lavage should be considered a crucial factor in TKA to improve implant fixation, which cannot be compensated for by cement application technique.     

高粘度骨水泥与低粘度骨水泥椎体成形术治疗骨质疏松性椎体压缩性骨折的疗效比较

目的 比较在椎体成形术中，高粘度骨水泥和低粘度骨水泥治疗骨质疏松性椎体压缩性骨折的临床疗效差异。方法 回顾性分析83例骨质疏松性椎体压缩性骨折患者，接受椎体成形术后的病例资料。其中采用低粘度骨水泥椎体成形术患者43例；采用高粘度骨水泥椎体成形术患者40例。记录单个椎体手术时间、骨水泥渗漏发生率，术后并发症发生率。利用视觉模拟评分及功能障碍指数评分对两组进行术前及术后一天、术后三个月疼痛及功能评价。通过X线片对术前、术后椎体各部进行测量，统计椎体高度变化。结果 83例患者均得到随访，通过对两组的各项指标比较，在术前视觉模拟评分和术前骨折压缩率上无明显统计学差异。在手术时间上高粘度组较低粘度骨水泥组明显缩短（t=22.32，P=0.000）。高粘度骨水泥组和低粘度骨水泥组的术后一日、术后三个月视觉模拟评分、功能障碍指数评分较术前明显降低，组内差异有高度显著性（P=0.000），组间无明显差异。高粘度组骨水泥渗漏率较低粘度骨水泥组明显降低，差异有统计学意义（P=0.0494）。椎体成形术后高粘度骨水泥组椎体高度恢复优于低粘度骨水泥组，差异有显著统计学意义（P=0.000）。结论 椎体成形术中使用不同类型的骨水泥都能有效的缓解病人疼痛，改善生活质量。与低粘度骨水泥相比，高粘度骨水泥有着较低的骨水泥渗漏率，同时缩短了手术时间和减少放射性的暴露。高粘度骨水泥在治疗骨质疏松性椎体压缩性骨折方面有一定的优势。     

高黏度与低黏度骨水泥应用于经皮椎体后凸成形术的疗效比较

目的比较高黏度与低黏度骨水泥在经皮椎体后凸成形术(PKP)中应用的临床疗效。方法对60例骨质疏松性椎体压缩性骨折患者行PKP治疗。采用随机抽签法分为对照组和实验组,每组30例,对照组使用低黏度骨水泥,实验组使用高黏度骨水泥。比较两组患者疼痛VAS评分、ODI、生活质量SF-36评分、伤椎高度恢复及骨水泥渗漏率、术后骨水泥肺栓塞发生率情况。结果术后实验组:VAS评分1.7分±0.8分,ODI 22.6分±3.6分,SF-36评分85.5分±12.1分,Cobb角15.2°±2.1°,椎体高度19.9 mm±0.9 mm;术后对照组:VAS评分2.6分±1.3分,ODI 28.3分±4.5分,SF-36评分70.3分±11.2分,Cobb角19.7°±2.4°,椎体高度18.5 mm±0.6 mm;以上各项两组比较差异均有统计学意义(P0.05)。实验组骨水泥渗漏及术后近期肺栓塞发生率均低于对照组(P0.05)。结论在PKP治疗椎体压缩性骨折中,采用高黏度骨水泥临床疗效好,并发症少。     

Nanocrystalline hydroxyapatite facilitates bone apposition to polymethylmethacrylate: Histological investigation using a sheep model

Polymethylmethacrylate (PMMA) is the most commonly used bone void filler for vertebral augmentation in osteoporotic fracture. It provides mechanical stability and immediate pain relief; however, PMMA is not osteointegrated and is separated from the surrounding bone tissue by a thin fibrous layer. The aim of this study was to investigate the effect of nanocrystalline hydroxyapatite (HA) on osteointegration of PMMA in a sheep model. A composite material, consisting of PMMA and nanocrystalline HA (70:30, v/v), was implanted in one distal femur, with pure PMMA in the other femur as a control. Three and 6 months after implantation, the distal femora were histologically investigated. All composite implants exhibited a tight junction to the surrounding bone tissue, with minimal bone ingrowth into the outer surface of the implant. In comparison, with use of the control implants, we observed an overall bone resorption around pure PMMA, with fibrous connective tissue encapsulating the implant. These results suggest that nanocrystalline HA enables osteointegration of PMMA in bone tissue, which might alter the biomechanical characteristics of the osteoporotic vertebral body after augmentation. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1290–1295, 2012