金属对金属髋关节动态边缘接触力学行为

目的研究球面共型接触人工髋关节在股骨头动态位移条件下的边缘接触力学行为。方法基于所发展的有限元球面网格数据模型,动态模拟分析金属对金属人工髋关节在给定生理位移工况条件下的接触行为和可能诱发的边缘接触现象。结果数值模拟表明,随着动态位移载荷的增加,关节接触面压力合力的垂直分力和水平分力都有上升趋势;在边缘接触过程中压力合力的垂直分力比非边缘接触情况变化趋势要缓慢,但相应的水平分力增大趋势更显著。此外,边缘接触与非边缘接触对应的接触压力分布形态与接触区域也各不相同。结论金属对金属人工关节髋臼相对股骨头过大的倾斜状态极易引起边缘接触,动态边缘接触情况下,将导致股骨头向髋臼内侧产生相对滑动及附加磨损的可能,这对临床人工髋关节磨损评估与关节制造发展提供了分析依据。     

非球面人工髋关节接触力学

目的由于受制造技术的局限性、可能的设计优化考虑以及临床应用的磨损等因素影响,人工髋关节轴承表面表现为非球面几何特征,可以利用有限元分析方法对非球面人工髋关节的接触力学行为进行研究。方法对球面网格数据模型进行非球关节面重建,研究不同取向椭球面股骨头对球面髋臼几何特征的非球面金属对金属人工髋关节的接触力学表现。结果非球面股骨头接触区域中心位置的平均曲率半径在一定范围内增大时,能有效降低相应关节接触面上的最大接触压力,同时接触面积有所增加;在同样载荷下,髋臼相对股骨头不同倾斜状态对非球面股骨头的接触压力峰值和面积影响较小,但压力分布有所不同。结论良好地控制人工髋关节的非球表面特征,有利于改善人工髋关节最大接触压力幅值大小和接触区域分布。所发展的非球面人工髋关节接触模型及数值模拟过程能够有效地运行,这为非球面关节动态接触及磨损预测问题研究提供了条件。     

金属对金属人工髋关节边缘接触效应

目的 研究金属对金属人工髋关节不同行走姿态下的接触力学行为,特别是大幅度运动可能导致的边缘接触效应。方法 建立球面共型接触的髋关节有限元模型,通过改变髋臼相对股骨头的倾斜状态和对股骨头施加恒定竖直方向载荷相结合,等效模拟分析人工髋关节不同行走姿态下的接触状态。结果 髋臼相对股骨头倾角在小于约60°范围内增加时,其对应的最大接触压力呈下降趋势,接触面积有所增大;当倾角超过80°范围时,关节接触区域因靠近髋臼边缘,最大接触压力位置由初始接触点向髋臼倾斜方向移动了约6°~9°的位置,用以满足压力分布合力与外载荷的平衡,接触压力和分布范围有所增加。结论 髋臼相对股骨头较大倾斜状态极易引起不同的边缘接触现象,置换人体髋关节产生的边缘接触问题需要引起临床外科和关节制造上的重视。     

材料匹配与人工髋关节接触性能分析

目的 研究当前临床常用的不同材料匹配的典型人工髋关节接触力学性能。方法 建立球基共型接触人工髋关节的有限元模型;通过施加恒定竖直方向载荷,等效模拟关节正常行走情况下的接触力学,分析材料匹配球面的接触性能及评估相应的磨损预测。结果 获得具有诸如金属对金属（MOM）、金属对陶瓷(MOC)、陶瓷对陶瓷(COC)、陶瓷对聚合物(COP)、金属对聚合物(MOP)5种材料组配条件下的人工髋关节接触性能数值分析;结果显示其接触应力由大到小排列分别为COC、MOC、MOM、COP和MOP;而接触面积由大到小排列分别为MOP、COP、MOM、MOC和COC。结论 高弹性模量和低泊松比的材料匹配的人工髋关节变形量较小,但会导致局部应力较大;将低弹性模量和高泊松比的柔性材料聚乙烯作为髋臼,则不会出现较大的接触应力集中,但变形量较大,且出现边缘受力情况。另一方面,MOM和MOC材料匹配的人工髋关节具有较低的接触磨损性能,对临床上人工髋关节选材提供参考价值。     

一种使用非球面髋臼的金属-金属髋关节假体的时变弹流润滑分析

目的 金属－金属人工髋关节的高效润滑特性只需在主承载区上有适宜的匹配性,其优点是增加边缘区间隙。通过改变假体表面的曲率半径,得到变化的间隙。Alpharabola就是这种表面的具体结构之一。本文的研究目的是观察采用Alpharabola杯的新型假体在实际步态条件下的弹性流体动力润滑（EHL）性能。方法 建立新型髋关节假体的EHL模型,根据ISO规定的动载运动条件来表示人体步态。利用多重网格技术,求解球坐标系下的雷诺方程、膜厚方程和载荷平衡方程以获得完整数值解。结果 在一个收敛步态周期中,分析润滑膜轮廓和压力分布详细变化。观察参数?对中心膜厚、最小膜厚和中心压力的准稳态和非稳态解的影响,并比较相同?下非稳态解和准稳态解。在非稳态条件和准稳态条件下,比较Alpharabola髋关节假体和球形髋关节假体润滑性能。结论 结果发现,在实际步态条件下,挤压膜效应和非球形髋臼表面能显著提高润滑性能,即估计的润滑膜厚增加且最大流体压力减少。这说明金属－金属Alpharabola髋关节假体比球形髋关节假体能显著地增强流体润滑。 关键词：非稳态弹性流体动力润滑;金属－金属髋关节假体;非球形支承表面;Alpharabola髋臼表面     

大直径金属/金属股骨头人工全髋关节置换治疗股骨头缺血坏死**☆

背景：与以往大直径股骨头的高磨损率和高髋臼松动率相比,新一代大直径金属对金属全髋关节有着更长的使用寿命和低磨损,低脱位率等优点。 目的：评价应用大直径金属/金属股骨头人工全髋关节置换术治疗股骨头缺血坏死的临床疗效。 方法：回顾性分析26例股骨头缺血坏死患者实施单侧大直径金属/金属股骨头人工全髋关节置换资料。 结果与结论：所有患者均获得随访,在随访期内影像学显示假体位置良好,无假体松动,脱位等并发症。Harris评分由置换前49.5分改善为置换后92.5分,优良率为96%,总体满意率为96%。置换前后及随访时未发生假体松动、脱位、感染等不良反应。说明大直径金属/金属股骨头全髋关节置换治疗股骨头缺血坏死可获得较好的疗效,短期内无明显肾功能变化。     

Cam型髋关节撞击综合征关节软骨接触力学的有限元分析

目的 通过有限元方法探讨不同严重程度的Cam型髋关节撞击综合征(femoroacetabular impingement,FAI)关节软骨接触力学的变化。方法 建立正常髋关节及不同α角的 Cam型FAI髋关节三维有限元模型,计算行走、坐下、起立等日常活动下的关节软骨接触压力和应力。结果 完整步态周期加载过程中,不同α角的Cam型FAI软骨接触压力分布与正常髋关节接近,无高接触压力和Von Mises应力集中区域;坐下、起立加载过程中,Cam型FAI软骨接触压力均大于正常髋关节,且随α角的增加而增大,其接触区域主要位于髋臼缘前上方,局部出现过高压力和Von Mises应力集中。结论 Cam型FAI软骨接触力学变化的关键影响因素是运动方式,关节软骨过高的接触压力和Von Mises应力,可能是其引起软骨退变并最终导致骨性关节炎的力学原因。     

陶瓷对陶瓷人工髋关节的磨擦界面特征

背景：陶瓷对陶瓷人工髋关节假体在临床上已有一定的应用,在表面磨擦、磨损和润滑方面占有优势,具有很大的研发潜力。 目的：评价陶瓷对陶瓷人工髋关节表面磨擦、磨损和润滑特性。 方法：将金属对超高分子量聚乙烯、金属对金属以及陶瓷对陶瓷人工髋关节假体的磨损界面研究进行分析,了解氧化铝陶瓷材料的结构特点、制备工艺以及磨损参数,并分析陶瓷对陶瓷人工髋关节置换治疗的效果,与其它假体材料进行对比。 结果与结论：①金属对超高分子量聚乙烯人工髋关节抗磨损性能差,使磨损颗粒进入关节和周围组织,造成骨溶解和松动。②金属对金属人工髋关节的磨损性能较金属对超高分子量聚乙烯假体有很大改善,骨溶解的发生率非常少,但由于磨损颗粒可散布于体内各脏器和体液中,使用时要注意避免发生过敏反应和毒性。③体外试验和体内试验证明陶瓷对陶瓷人工髋关节具有良好的摩擦、磨损、润滑性能,临床治疗长期随访结果显示陶瓷对陶瓷人工髋关节假体置换后无磨损颗粒,不会发生骨溶解。对于年龄较小,并且对髋关节活动度有较高要求的患者,陶瓷对陶瓷人工髋关节是治疗的首选。随着陶瓷对陶瓷人工髋关节假体设计和材料学的发展,通过改进假体的机械学特性,提高摩擦界面的耐磨性能和润滑机制,陶瓷对陶瓷人工髋关节假体的远期临床疗效将更加满意。     

氧化锆金属及在人工关节中的应用

金属-超高分子量聚乙烯（UHMWPE）近半个世纪来一直是人工关节的标准配伍，被广泛地应用于人工髋关节、人工膝关节、人工肩关节、人工踝关节等。然而，随着人们期望寿命的增加、对生活质量要求的提高，这一假体配伍越来越成为制约人工关节置换术后远期效果进一步改善的重要因素。其根本原因是：这一“硬-软”配对的人工关节中，UHMWPE的磨损无法完全避免。磨损不仅限制了假体的使用寿命，而且所产生的碎屑触发了最终导致骨溶解的生物反应。两者的结果都与人工关节置换术后使用期限的有限直接相关。[第一段]     

人工髋关节超高分子量聚乙烯磨粒分析的现状及趋势

简要介绍了目前国内外分析人工髋关节磨粒的技术,评述了在各种实验方法条件下生成的人工髋关节超高分子量聚乙烯(ultra-high molecular weight polyethylene,UHMWPE)磨粒的种类及特性、人工髋关节的磨损机制以及影响其磨损机制的因素,阐述了建立人工髋关节磨粒图谱的重要作用及意义,并对未来的研究重点进行了展望。应加强磨粒形貌特性与人工髋关节磨损机制之间的相互关系研究,以及在考虑生物化学环境和力学作用等因素协同作用条件下建立合适的人工髋关节磨损预测模型的研究。这对于人工关节置换的临床应用研究以及生物摩擦学的深入发展都具有重要的理论价值和现实意义。     

Lubrication and friction prediction in metal-on-metal hip implants

A general methodology of mixed lubrication analysis and friction prediction for a conforming spherical bearing in hip implants was developed, with particular reference to a typical metal-on-metal hip replacement. Experimental measurement of frictional torque for a similar implant was carried out to validate the theoretical prediction. A ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup under cyclic operating conditions of representative load and motion. The mixed lubrication model presented in this study was first applied to identify the contact characteristics on the bearing surfaces, consisting of both fluid-film and boundary lubricated regions. The boundary lubricated contact was assumed to occur when the predicted fluid film thickness was less than a typical boundary protein layer absorbed on the bearing surfaces. Subsequently, the friction was predicted from the fluid-film lubricated region with viscous shearing due to both Couette and Poiseuille flows and the boundary protein layer contact region with a constant coefficient of friction. The predicted frictional torque of the typical metal-on-metal hip joint implant was compared with the experimental measurement conducted in a functional hip simulator and a reasonably good agreement was found. The mixed lubrication regime was found to be dominant for the conditions considered. Although the percentage of the boundary lubricated region was quite small, the corresponding contribution to friction was quite large and the resultant friction factor was quite high.     

Contact mechanics studies of an ellipsoidal contact bearing surface of metal-on-metal hip prostheses under micro-lateralization

The morphology of the contact bearing surfaces plays an important role in the contact mechanics and potential wear of metal-on-metal (MOM) hip prostheses. An ellipsoidal bearing surface was proposed for MOM hip implants and the corresponding contact mechanics were studied by using the finite element method (FEM) under both standard and micro-lateralization conditions. When under micro-lateralization, the maximum contact pressure decreased from 927.3 MPa to 203.0 MPa, with increased ellipticity ratio medial-laterally. And the contact region was found to shift from the rim of the cup to the inner region compared to the spherical design. Under standard conditions, an increasing trend of the maximum contact pressure for the acetabular component was predicted as the major radius of the ellipsoidal bearing surface was increased. Nevertheless, the maximum contact pressure reached an asymptotic value when the ellipticity ratio was increased to 1.04. Therefore it is critical to optimize the ellipticity ratio in order to reduce the contact pressure under micro-lateralization condition and yet not to cause a markedly increased contact pressure under normal condition. Additionally, the maximum contact pressure in the ellipsoidal bearing surface remained relatively constant with the increased micro-lateralization. It is concluded that an ellipsoidal bearing surface morphology may be a promising alternative by offering better contact mechanisms when micro-lateralization should occur and attributing to minimized wear.     

Effect of 3D physiological loading and motion on elastohydrodynamic lubrication of metal-on-metal total hip replacements

An elastohydrodynamic lubrication (EHL) simulation of a metal-on-metal (MOM) total hip implant was presented, considering both steady state and transient physiological loading and motion gait cycle in all three directions. The governing equations were solved numerically by the multi-grid method and fast Fourier transform in spherical coordinates, and full numerical solutions were presented included the pressure and film thickness distribution. Despite small variations in the magnitude of 3D resultant load, the horizontal anterior–posterior (AP) and medial–lateral (ML) load components were found to translate the contact area substantially in the corresponding direction and consequently to result in significant squeeze-film actions. For a cup positioned anatomically at 45°, the variation of the resultant load was shown unlikely to cause the edge contact. The contact area was found within the cup dimensions of 70–130° and 90–150° in the AP and ML direction respectively even under the largest translations. Under walking conditions, the horizontal load components had a significant impact on the lubrication film due to the squeeze-film effect. The time-dependent film thickness was increased by the horizontal translation and decreased during the reverse of this translation caused by the multi-direction of the AP load during walking. The minimum film thickness of 12–20 nm was found at 0.4 s and around the location at (95, 125)°. During the whole walking cycle both the average and centre film thickness were found obviously increased to a range of 40–65 nm, compared with the range of 25–55 nm under one load (vertical) and one motion (flexion–extension) condition, which suggested the lubrication in the current MOM hip implant was improved under 3D physiological loading and motion. This study suggested the lubrication performance especially the film thickness distribution should vary greatly under different operating conditions and the time and location that potential wear may occur was very sensitive to specific loading and motion conditions. This may provide some explanation to the large variations in wear from hip simulators and clinical studies, and also stress the importance of using more realistic loading and motion conditions in the tribological study of MOM hip prostheses.     

Multibody dynamic simulation of knee contact mechanics

Multibody dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to knee joint degeneration and restoration. Current three-dimensional multibody knee models are either quasi-static with deformable contact or dynamic with rigid contact. This study proposes a computationally efficient methodology for combining multibody dynamic simulation methods with a deformable contact knee model. The methodology requires preparation of the articular surface geometry, development of efficient methods to calculate distances between contact surfaces, implementation of an efficient contact solver that accounts for the unique characteristics of human joints, and specification of an application programming interface for integration with any multibody dynamic simulation environment. The current implementation accommodates natural or artificial tibiofemoral joint models, small or large strain contact models, and linear or nonlinear material models. Applications are presented for static analysis (via dynamic simulation) of a natural knee model created from MRI and CT data and dynamic simulation of an artificial knee model produced from manufacturer's CAD data. Small and large strain natural knee static analyses required 1 min of CPU time and predicted similar contact conditions except for peak pressure, which was higher for the large strain model. Linear and nonlinear artificial knee dynamic simulations required 10 min of CPU time and predicted similar contact force and torque but different contact pressures, which were lower for the nonlinear model due to increased contact area. This methodology provides an important step toward the realization of dynamic musculoskeletal models that can predict in vivo knee joint motion and loading simultaneously.     

金属对金属大直径髋关节假体置换5年：21例全部随访评价

背景：金属对金属全髋假体因其具有良好的活动度因而被广泛应用于人工全髋关节置换。 目的：探讨金属对金属大直径髋关节假体置换中期临床效果。 方法：选择2004-04/2005-06在河北省大城县第二医院骨科行金属对金属髋关节假体置换的21例中青年患者,均在腰硬联合麻醉下完成金属对金属大直径髋关节假体置换,由同一医生通过门诊复查、电话以及信函等方式进行随访,统计置换后5年患者患侧髋关节Harris关节评分、关节活动度和所发生的并发症。 结果与结论：5年随访时21髋的髋关节Harris评分平均(94.3±1.6)分,均达到优水平,患侧关节屈曲(111.2±14.3)°、外展(40.3±3.4)°、内收(23.5±2.4)°、外旋(54.8±3.7)°、内旋(20.9±2.1)°,且未发现关节脱位者,1髋出现轻度骨溶解(4.8%),2髋出现植入物松动,2髋出现髋关节周围疼痛,且均发生在置换后6个月以后,持续超过5年以上。说明金属对金属大直径全髋关节置换后患者中期稳定性好,关节活动功能恢复效果佳,且疼痛发生率低,尤其是对于中青年患者,具有较好的临床应用价值。     

Wear evaluation of cobalt-chromium alloy for use in a metal-on-metal hip prosthesis

Wear of the polyethylene in total joint prostheses has been a source of morbidity and early device failure, which has been extensively reported in the last 20 years. Although research continues to attempt to reduce the wear of polyethylene joint-bearing surfaces by modifications in polymer processing, there is a renewed interest in the use of metal-on-metal bearing couples for hip prostheses. Wear testing of total hip replacement systems involving the couple of metal or ceramic heads on polymeric acetabular components has been performed and reported, but, until recently, there has been little data published for pin-on-disk or hip-simulator wear studies involving the combination of a metallic femoral head component with an acetabular cup composed of the same or a dissimilar metal. This study investigated the in vitro wear resistance of two cobalt/chromium/molybdenum alloys, which differed primarily in the carbon content, as potential alloys for use in a metal-on-metal hip-bearing couple. The results of pin-on-disk testing showed that the alloy with the higher (0.25%) carbon content was more wear resistant, and this alloy was therefore chosen for testing in a hip-simulator system, which modeled the loads and motions that might be exerted clinically. Comparison of the results of metal-on-polyethylene samples to metal-on-metal samples showed that the volumetric wear of the metal-on-polyethylene bearing couple after 5,000,000 cycles was 110-180 times that for the metal-bearing couple. Polyethylene and metal particles retrieved from either the lubricant for pin-on-disk testing or hip simulator testing were characterized and compared with particles retrieved from periprosthetic tissues by other researchers, and found to be similar. Based upon the results of this study, metal-on-metal hip prostheses manufactured from the high carbon cobalt/chromium alloy that was investigated hold sufficient promise to justify human clinical trials.