The effect of the design of the femoral component on the conformity of the patellofemoral joint in total knee replacement

One of the most controversial issues in total knee replacement is whether or not to resurface the patella. In order to determine the effects of different designs of femoral component on the conformity of the patellofemoral joint, five different knee prostheses were investigated. These were Low Contact Stress, the Miller-Galante II, the NexGen, the Porous-Coated Anatomic, and the Total Condylar prostheses. Three-dimensional models of the prostheses and a native patella were developed and assessed by computer. The conformity of the curvature of the five different prosthetic femoral components to their corresponding patellar implants and to the native patella at different angles of flexion was assessed by measuring the angles of intersection of tangential lines. The Total Condylar prosthesis had the lowest conformity with the native patella (mean 8.58 degrees ; 0.14 degrees to 29.9 degrees ) and with its own patellar component (mean 11.36 degrees ; 0.55 degrees to 39.19 degrees ). In the other four prostheses, the conformity was better (mean 2.25 degrees ; 0.02 degrees to 10.52 degrees ) when articulated with the corresponding patellar component. The Porous-Coated Anatomic femoral component showed better conformity (mean 6.51 degrees ; 0.07 degrees to 9.89 degrees ) than the Miller-Galante II prosthesis (mean 11.20 degrees ; 5.80 degrees to 16.72 degrees ) when tested with the native patella. Although the Nexgen prosthesis had less conformity with the native patella at a low angle of flexion, this improved at mid (mean 3.57 degrees ; 1.40 degrees to 4.56 degrees ) or high angles of flexion (mean 4.54 degrees ; 0.91 degrees to 9.39 degrees ), respectively. The Low Contact Stress femoral component had the best conformity with the native patella (mean 2.39 degrees ; 0.04 degrees to 4.56 degrees ). There was no significant difference (p > 0.208) between the conformity when tested with the native patella or its own patellar component at any angle of flexion. The geometry of the anterior flange of a femoral component affects the conformity of the patellofemoral joint when articulating with the native patella. A more anatomical design of femoral component is preferable if the surgeon decides not to resurface the patella at the time of operation.     

氧化锆大颗粒诱导兔膝关节周围组织无菌性炎症及其机制

目的 观察氧化锆大颗粒对兔膝关节周围组织无菌性炎症的作用并探讨其机制.方法 取日本大耳白兔15只,随机分为氧化锆颗粒组、超高分子量聚乙烯(UHMWPE)颗粒组和对照组,每组5只.兔右侧膝关节腔及关节内侧组织分别注入浓度为0.1％ (V/V)、直径为58.87 μm的氧化锆颗粒混悬液、UHMWPE颗粒混悬液,对照组只注入等量磷酸盐缓冲液(PBS).实验第24周取膝关节周围组织,行病理组织学检查,酶联免疫吸附试验(ELISA)检测标本组织匀浆中白细胞介素(IL) -1β、IL-6、肿瘤坏死因子(TNF)-α水平.结果 UHMWPE颗粒组可见颗粒周围有大量巨噬细胞、多核巨细胞与成纤维细胞包裹;氧化锆颗粒组细胞数较对照组增加,但明显少于UHMWPE颗粒组.UHMWPE颗粒组IL-1β、IL.-6、TNF-o水平均明显高于氧化锆颗粒组(P＜0.05).氧化锆颗粒组IL-1β、IL-6、TNF-α水平明显高于对照组(P＜0.05).结论 氧化锆颗粒诱导兔膝关节无菌性炎症作用弱于UHMWPE颗粒,其机制与炎性因子IL-1β、IL-6、TNF-α有关.     

The effects of conformity and load in total knee replacement

The effects of different conformity ratios and loads on the ultrahigh molecular weight polyethylene stress levels acting on knee implants were examined using a nonlinear, finite element analysis. The contact condition between a rigid cylinder with a radius of 30 mm and a polyethylene plate was modeled. Nonlinear behavior of polyethylene was assumed. The polyethylene plate was constructed with varying radii, with a minimal thickness of 6 mm and with a width of 40 mm. The ratio of the cylinder radius to the radius of the polyethylene plate was defined as the conformity ratio; a conformity ratio of 0 represented a flat tibial inlay, whereas the highest ratio modeled of 0.99 was nearly conforming. The conformity ratios modeled were 0, 0.2, 0.4, 0.6, 0.7, 0.8, 0.9, 0.95, and 0.99. The loads applied were 1000 N, 2000 N, 3000 N, 4000 N, 5000 N, and 6000 N. The effects of different conformity ratios and loads on the contact area (mm2), the compressive surface stress (MPa), the shear stress (MPa), and the von Mises stress (MPa) were investigated. It was found that all of these parameters were affected by changes to the conformity ratio and to a lesser extent by load changes. That is, increasing the load from 3000 N to 6000 N resulted in a surface and shear stress increase lower than the increase in stress caused by the small change of the conformity ratio from 0.99 to 0.95. The effect of an increasing conformity ratio on the reduction in stress was more pronounced for conformity ratios above 0.8. In addition, the effect of a load increase for a flat tibial inlay was two times greater than for one with near full conformity.     

Analysis of polyethylene thickness of tibial components in total knee replacement

BACKGROUND: Excessive wear of the polyethylene bearing surfaces of tibial components has become an important factor in early failure of total knee arthroplasty. Inadequate thickness of the polyethylene insert is one cause of excessive wear, and various minimum thicknesses have been recommended in order to reduce contact stresses within the polyethylene. However, the true thicknesses of modular polyethylene tibial inserts typically are not stated accurately by the manufacturers in their product information. The purpose of this study was to determine whether the information about the thickness of tibial inserts supplied by the manufacturers is adequate. METHODS: Five of the thinnest available polyethylene tibial inserts from five different manufacturers were selected. The minimum thickness of each was measured with use of a Sigma electronic micrometer comparator to an accuracy of +/-0.005 mm. RESULTS: The stated thicknesses of the polyethylene tibial inserts were 8, 9, and 10 mm, values that differed markedly from the actual minimum thicknesses, which ranged from 5.5722 to 6.2048 mm (mean values). CONCLUSION: The thickness of polyethylene tibial inserts has been implicated as a potential cause of excessive wear and early failure of total knee replacements. This paper highlights the fact that the information supplied by the manufacturers is inaccurate and potentially misleading; in one case, the true thickness was much less than the recommended minimum thickness. We recommend that the minimum thickness of the tibial components as well as the combined thickness of the polyethylene insert and the metal tibial tray be specified in the product information and on the packaged insert.     

聚乙烯磨损颗粒的大小对人工关节松动的影响

目的　探讨超高分子聚乙烯磨损颗粒 (UHMWPE)的大小对人工关节松动的影响。方法　从翻修髋关节术所获得组织中提取超高分子聚乙烯磨损颗粒 (平均直径 9.41、5 .96、0 .5 6、0 .3 3 μm ) ,将其与Ceridust 3 615 R○ 颗粒 (模型颗粒 ) (平均直径 14 .2 7、6.3 9、1.74、1.0 1、0 .5 4和 0 .2 8μm)分别刺激人单核 /巨噬细胞 ,并检测培养上清液中的骨溶解介质。 结果　随着UHMWPE颗粒直径的减少 ,其刺激单核 /巨噬细胞分泌白细胞介素 1β ,白细胞介素 6和细胞坏死因子α的作用明显增强 ,而Ceridust 3 615 R○ 颗粒的大小对单核 /巨噬细胞的刺激作用影响不明显。结论　单核 /巨噬细胞对UHMWPE磨损颗粒与Ceridust 3 615 R○ 颗粒的反应明显不同 ,运用模型颗粒研究人工关节松动的机制仍须谨慎。     

Position of the prosthesis components in total ankle replacement and the effect on motion at the replaced joint

Purpose  

In some cases of total ankle replacement, perfect alignment of the prosthetic components is not achieved. This study analyses the extent to which component positioning is critical for the final range of motion.     

The effect of prophylaxis for thrombosis on heterotopic ossification following total hip joint replacement

The effect of prophylaxis for thrombosis on heterotopic ossification was investigated using 216 total hip joint endoprostheses implanted between 1976 and 1978. During this period a random comparative study of low dose heparin and oxyphenbutazone/acetylsalycilic acid was carried out. The rate of ossification in the 216 hip joints was 17.6%, and was about average for the values specified in literature on this subject. Heterotopic ossification occurred in 30.1% of the 103 hip joints treated with heparin, whilst the rate of ossification in the 113 hip joints treated with oxyphenbutazone/acetylsalycilic acid was only 6.2%. This represents a statistically significant difference in disfavour of prophylaxis with heparin.     

The effect of prophylaxis for thrombosis on heterotopic ossification following total hip joint replacement

Summary The effect of prophylaxis for thrombosis on heterotopic ossification was investigated using 216 total hip joint endoprostheses implanted between 1976 and 1978. During this period a random comparative study of low dose heparin and oxyphenbutazone / acetylsalycilic acid was carried out. The rate of ossification in the 216 hip joints was 17.6%, and was about average for the values specified in literature on this subject. Heterotopic ossification occurred in 30.1% of the 103 hip joints treated with heparin, whilst the rate of ossification in the 113 hip joints treated with oxyphenbutazone / acetylsalycilic acid was only 6.2%. This represents a statistically significant difference in disfavour of prophylaxis with heparin.

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Zusammenfassung Der Einflu? der Thromboseprophylaxe auf periartikul?re Verkn?cherungen wurde bei 216 Hüfttotalendoprothesen der Jahre 1976–1978 untersucht. In diesem Zeitraum lief eine randomisierte, vergleichende Studie zwischen low dose-Heparin und Oxyphenbutazon / Acetylsalycils?ure. Die Verkn?cherungsrate der 216 Hüftgelenke betrug 17,6% und lag somit im Durchschnitt der in der Literatur angebenen Werte. Bei den 103 mit Heparin behandelten Hüftgelenken traten in 30.1% der F?lle periartikulare Verkn?cherungen auf, w?hrend die Verkalkungsrate bei den 113 Hüftgelenken mit Oxyphenbutazon / Acetylsalycils?ure-Prophylaxe nur 6,2% betrug. Dies ist ein statistisch signifikanter Unterschied zuungunsten der Heparinprophylaxe.

     

Influence of glenohumeral conformity on glenoid stresses after total shoulder arthroplasty

Glenohumeral conformity has been reported to be one of the most critical implant-related features that may affect the occurrence of glenoid loosening. This study evaluated the mechanical effects of this parameter with a 3-dimensional finite element model of a prosthetic shoulder, which included the scapula, the humerus, and the rotator cuff muscles. Aequalis humeral and glenoid components were implanted numerically according to manufacturer's recommendations for 2 different orientations of the glenoid component (0 degrees and 15 degrees of retroversion). Different values of glenohumeral conformity (1-15 mm of radial mismatch) were tested by a progressive flattening of the glenoid surface. Free and countered rotation movements were simulated. Glenohumeral contact pressure, cement stress, shear stress, and micromotions at the bone-cement interface were calculated. At 0 degrees of retroversion, conformity had only a slight effect, whereas at 15 degrees of retroversion, all quantities increased by more than 200% and exceeded critical values above 10 mm of mismatch.     

The effect of ultra-high molecular weight polyethylene wear debris on MG63 osteosarcoma cells in vitro

BACKGROUND: Focal osteolysis due to ultra-high molecular weight polyethylene wear debris involves effects on both bone resorption and bone formation. METHODS: The response of MG63 osteoblast-like osteosarcoma cells to ultra-high molecular weight polyethylene wear debris isolated by enzymatic digestion of granulomatous tissue obtained from the sites of failed total hip arthroplasties was examined. Scanning electron microscopy, particle-size analysis, and Fourier transform infrared spectroscopy were used to characterize the number, morphology, size distribution, and chemical composition of the particles. Cell response was assessed by adding particles at varying dilutions to confluent cultures and measuring changes in cell proliferation (number of cells and [3H]-thymidine incorporation), osteoblast function (alkaline-phosphatase-specific activity and osteocalcin production), matrix production (collagen production and proteoglycan sulfation), and local cytokine production (prostaglandin-E2 production). RESULTS: The mean size of the particles was 0.60 micrometer, and 95 percent of the particles had a size of less than 1.5 micrometers. The number of particles per gram of tissue ranged from 1.39 to 3.38x10(9). Three of the four batches of particles were endotoxin-free. Exposure of the cells to particles of wear debris significantly increased the number of cells (p<0.05) and the [3H]-thymidine incorporation (p<0.05) in a dose-dependent manner. In contrast, the addition of particles decreased alkaline-phosphatase-specific activity and osteocalcin production. Collagen production and proteoglycan sulfation were also decreased, while prostaglandin-E2 synthesis was increased by the addition of particles. CONCLUSIONS: Ultra-high molecular weight polyethylene particles isolated from human tissue stimulated osteoblast proliferation and prostaglandin-E2 production and inhibited cell differentiation and matrix production. These results indicate that particles of wear debris inhibit cell functions associated with bone formation and that osteoblasts may produce factors in response to wear debris that influence neighboring cells, such as osteoclasts and macrophages. CLINICAL RELEVANCE: Particles of wear debris, especially ultra-high molecular weight polyethylene, have been implicated in the loosening of implants and the development of osteolysis. The present study shows that particles of ultra-high molecular weight polyethylene isolated from human tissue inhibit osteoblast functions associated with bone formation. In addition, particles of wear debris induced osteoblasts to secrete factors capable of influencing neighboring cells, such as osteoclasts and macrophages. These results suggest that osteoblasts may play a role in the cascade of events leading to granuloma formation, osteolysis, and failure of orthopaedic implants.     

Thrombosis prophylaxis with low molecular weight heparin in total hip replacement

In a randomized prospective trial, the efficacy of low molecular weight heparin (LMWH) (Fragmin) and dextran 70 (Macrodex) in preventing deep vein thrombosis (DVT) in the legs was evaluated in 98 consecutive patients undergoing elective total hip replacement. The patients were randomly allocated to receive either 2500 anti-factor Xa units LMWH twice daily for 7 days, with the first dose given 2 h before surgery; or 500 ml dextran 70 twice during the day of operation, followed by a single infusion of 500 ml on the first and again on the third postoperative day. DVT was assessed by 125I-fibrinogen test for 2 weeks postoperatively, a positive test being followed by phlebography. DVT developed in 22 (45 per cent) of 49 patients receiving dextran 70 and in 10 (20 per cent) of 49 patients in the LMWH group (P less than 0.01). LMWH was thus statistically significantly better than dextran 70 in preventing DVT in the legs. It was not firmly established whether this benefit was also valid in the high ileofemoral region. Two patients with non-fatal pulmonary embolism were found in each group. Per- and postoperative blood loss and blood transfusion requirements were significantly lower in the LMWH group.     

The effects of lower-extremity total joint replacement for arthritis on obesity

Total hip or knee replacement patients who are overweight or obese often consider their disabling joint disease a cause for their increased weight. This prospective study investigated weight change in 100 patients after successful total joint replacement to determine whether surgical treatment of hip or knee arthritis leads to weight reduction. Postoperatively, both hip and knee replacement patients gained weight, with no difference in weight gain between hip and knee replacement patients. Younger hip patients gained a significant amount of weight. Patients a with normal body mass index and obese patients did not lose weight, while overweight patients gained a significant amount of weight after surgery. These findings demonstrate successful treatment of lower-extremity arthritis does not lead to weight loss, and obesity should be treated as an independent disease that is not the result of inactivity from arthritis.     

Residual stresses in ultra-high molecular weight polyethylene loaded cyclically by a rigid moving indenter in nonconforming geometries

The characterization of stress and deformation fields that incorporate moving cyclic loads and nonlinear material response in ultra-high molecular weight polyethylene components for total knee replacements is required to quantify mechanisms of surface damage. A simulation of stresses in polyethylene components for total knee replacement subjected to cyclic moving loads was performed with use of nonlinear finite element analysis. Convergence to a steady-state cycle of stress and deformation was observed within five cycles of loading. Differential plastic deformation under the surface of the polyethylene led to horizontal residual stresses that were tensile at the surface and compressive in the subsurface. The magnitudes of the residual J stresses indicate their importance in surface failure mechanisms. Horizontal residual tensile stresses at the surface are consistent with the initiation and propagation of surface cracks that could cause pitting in polyethylene. Horizontal residual compressive stresses under the surface could cause such cracks to arrest or turn and thus limit damage to a region just beneath the surface. The results emphasize the importance of incorporating nonlinear effects to simulate long-term stress fields associated with surface damage in polyethylene.     

The instability of wrist joint and total wrist replacement

Total wrist arthroplasty are not used as widely as total knee and hip replacement. The functional hands are requiring surgeons to design a durable and functional satisfying prosthesis. This article will list the main reasons that cause the failure of the prosthesis. Some remarkable and representative prostheses are listed to show the devolvement of total wrist prosthesis and their individual special innovations to fix the problems. And the second part we will discuss the part that biomechanical elements act in the total wrist replacement (TWA). Summarize and find out what the real problem is and how we can find a way to fix it.     

The influence of material and design on total knee replacement wear

It is difficult for surgeons to make the decision on which design or material to use given the different options available. Marketing claims and direct-to-consumer advertising certainly complicate this further. One company may claim a higher percentage of wear reduction with their bearing surfaces compared with those of another manufacturer. If the percentage of wear reduction is lower, it is unclear as to whether this creates a more effective technology for reducing wear in the clinical situation. The relative contribution and relationship of design and materials to wear performance must be considered before making that important judgment. To examine the overall influence of implant design on wear reduction, a knee simulator study was undertaken. This simulator study compared the Oxinium Genesis II system with the Triathlon Conventional and Triathlon X3 knee systems under physiologic stair-climb loading and motion profiles. This allows a similar comparison of material effect within one design but also a global comparison across designs. Test results show the Triathlon Conventional and Triathlon X3 knee systems have superior wear resistance compared with that of the Genesis II Oxinium system under stair-climbing simulation. This finding indicates that implant design plays a more significant role in knee wear reduction than material. Although material technology may improve a given knee system's ability to wear, design geometry has a first-order effect and should be addressed before materials. This study represents an effort to differentiate design effect from two different approaches to material enhancement. The results of this study support the predominance of design in knee replacement wear performance. Ultimately, only clinical evidence such as published studies or outcomes reported in the available joint registries will establish whether any material or design can achieve a 30-year outcome.     

The effect of early bladder catheterization on the incidence of urinary complications after total joint replacement

A prospective, randomized study was performed in 54 female total arthroplasty patients to determine whether straight catheterization in the recovery room might reduce the incidence of postoperative urinary infection, urinary retention, and urinary catheterization. Thirty-one patients were straight catheterized in the recovery room; 23 were not. Overall, 13% of the patients developed a urinary tract infection postoperatively, 60% of the patients required at least one catheterization, and 13% of the patients required a Foley catheter. No beneficial effect of straight catheterization in the recovery room after arthroplasty was demonstrated.     

关于假体的设计与材料

关节假体目前面临最大的问题之一在于术后假体的松动,而导致松动最主要的原因是关节面磨损所产生的骨溶解效应.对于膝关节假体而言,一般的超高分子量聚乙烯(ultra-high molecuar weight polyethylene,UHMWPE)是目前胫骨衬垫的主要材料.众所周知,聚乙烯磨损颗粒是导致骨吸收的最重要因子,这就提出所谓交联聚乙烯,以用于减少磨损.与此同时,有研究指出,传统聚乙烯与交联聚乙烯所产生的磨损颗粒在尺寸及体积上呈现不同的结果[1,2].