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。     

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。     

金属对金属人工髋关节的磨损预测

目的发展复杂动态载荷与瞬态运动条件下的球面共型接触硬对硬人工髋关节的磨损预测模型,并用于典型的金属对金属人工髋关节在复杂三维生理运动条件下的磨损预测研究。方法建立有限元模型用于接触力学问题求解,采用固定-跟踪法(fixed-tracked method)完成具有三维欧拉运动的人工髋关节双侧界面动态磨损几何再现及相应的接触与磨损问题模拟的数值交换。结果磨损预测表明,磨损导致金属对金属人工髋关节接触界面几何由球面向非球面过渡,接触区域随磨损周期而增大,接触压力变化趋于平缓、最大接触压力逐渐减小。结论本研究所发展的三维复杂动态、具有双侧界面几何磨损变化的人工髋关节磨损预测模型,能够很好地进行金属对金属髋关节磨损数值预测模拟实验,为认识人工髋关节磨损机理提供了新的方法。     

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。     

髋臼发育不良性髋关节的三维有限元非线性接触压力分析

目的 从生物力学角度探讨髋臼覆盖程度(CE角)在髋臼发育不良引起的髋关节继发性骨关节炎中的作用。方法 建立正常、髋臼发育不良及髋臼过渡覆盖的髋关节三维有限元模型,应用非线性接触压力分析方法,观察髋臼发育不良性髋关节的关节软骨接触压力及软骨下骨应力分布。结果在所有的模型中,接触压力及应力均发生在股骨头最上部及与其相对应的髋臼顶穹部。在髋臼发育不良的模型中,另有过度不正常的接触压力发生在髋臼的后上缘区域。随着CE角的减小,接触压力和峰应力明显增高,接触面积下降。当CE角大于30°,压力分布类型及接触压力和峰应力改变不明显。结论髋臼覆盖程度降低所导致的生物力学改变在髋关节继发性骨关节炎中起重要作用。     

髋臼几何形态对髋关节接触力学行为的影响

目的研究髋臼解剖几何形态对髋关节接触力学特性的影响。方法建立人体天然髋关节的解剖学模型以及具有不同髋臼外形的简化模型,利用有限元分析方法研究步态载荷作用下髋关节的接触力学行为。结果 (1)解剖学模型产生的接触主要在髋臼的中上部,沿身体前后方向分布,峰值接触应力出现在髋臼前上部。(2)与解剖学模型相比,旋转椭球形髋臼产生了类似的接触分布,而球形和旋转蚶线形髋臼产生的接触主要在髋臼中部,沿上下方向;(3)旋转椭球形髋臼具有最大的接触面积和最小的峰值接触压力和Von-Mises应力;(4)球形髋臼和旋转蚶线形髋臼具有类似的接触力学特征。结论与球形和旋转蚶线形相比,旋转椭球形能够更好地描述髋臼的解剖形态及其接触力学行为。     

人工股骨头置换后的髋臼磨损

目的:探讨不同类型人工股骨头的临床应用特征、术后髋臼磨损及其影响因素和处理对策。方法:应用万方数据库和中国期刊全文数据库(CNKI),以"人工股骨头置换;全髋关节置换;髋臼磨损;临床意义;翻修技巧"等为检索词,检索1998/2010时限内与人工股骨头置换术后髋臼磨损有关的文献。排除重复研究或较陈旧文献。结果:依据纳入排除标准共保留文献24篇。临床常用的人工股骨头按材料类型不同分为金属合金股骨头与陶瓷材料股骨头。金属合金股骨头价格低廉,耐腐蚀,易于置入,但并发症严重;陶瓷股骨头安全性及有效性较高,但经济投入较高,不易临床推广。从临床效果来看,陶瓷股骨头引起髋臼磨损的发生率要远远低于金属合金类。髋臼磨损的影响因素涉及生物材料、假体设计、手术技巧等方面,全髋关节翻修为髋臼磨损的最后对策,需注意翻修技巧等。结论:陶瓷材料人工股骨头更适宜应用于人工股骨头置换术,其术后髋臼磨损的发生率较低。全髋关节翻修为髋臼磨损的最终治疗方案,其近、中期效果良好,长期效果有待进一步临床随访。     

Chiari骨盆截骨术中外展肌张力对股骨头软骨生物力学影响的三维有限元分析

目的　探讨Chiari骨盆截骨术中外展肌力负荷对股骨头软骨的生物力学影响。方法　建立Chiari骨盆截骨术的髋关节三维有限元模型，应用非线性接触压力分析方法，观察不同的外展肌力负荷条件下关节软骨接触压力及软骨下骨应力分布。结果　Chiari术后关节软骨的接触压力和股骨头软骨下骨应力明显降低，接触面积明显增加。随着外展肌力负荷的降低，接触压力的重新分布更加明显。对应于原髋臼软骨的压力逐渐降低，新髋臼软骨的压力逐渐升高。股骨头软骨下骨应力也进一步降低。而术后关节软骨的接触面积改变不大。结论　外展肌力负荷所引起的生物力学改变在Chiari骨盆截骨术中起重要作用。     

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。     

构建Cam型髋关节撞击综合征有限元模型及力学分析

背景:Cam型髋关节撞击综合征可使关节承受力学过载并最终导致髋关节骨关节炎,然而其诱发骨关节炎的相关力学机制仍不清楚。目的:运用三维有限元的方法,分析Cam型髋关节撞击综合征的关节内力学环境,进一步了解其病理力学特点。方法:采用正常髋关节CT数据,利用Mimics和Hypermesh软件准确构建正常髋关节和Cam型髋关节撞击综合征三维有限元模型。在LS-DYNA软件中,模拟坐下、起立时的力学加载条件,对正常髋关节和Cam型髋关节撞击综合征髋关节的软骨接触力学进行分析。结果与结论:基于CT数据准确构建了包含关节软骨的正常髋关节和Cam型髋关节撞击综合征髋关节三维有限元力学分析模型。坐下、起立加载过程中,正常髋关节在最大屈髋位时峰值接触压力分别为4.43,4.59 MPa;而Cam型髋关节撞击综合征髋关节分别为14.96,14.86 MPa,髋臼缘前上方出现过高压力和应力集中。提示髋臼软骨过高的接触压力可能是Cam型髋关节撞击综合征导致骨关节炎的力学机制。     

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.     

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.     

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     

The contact mechanics and occurrence of edge loading in modular metal-on-polyethylene total hip replacement during daily activities

The occurrence of edge loading in hip joint replacement has been associated with many factors such as prosthetic design, component malposition and activities of daily living. The present study aimed to quantify the occurrence of edge loading/contact at the articulating surface and to evaluate the effect of cup angles and edge loading on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR) during different daily activities. A three-dimensional finite element model was developed based on a modular MoP bearing system. Different cup inclination and anteversion angles were modelled and six daily activities were considered. The results showed that edge loading was predicted during normal walking, ascending and descending stairs activities under steep cup inclination conditions (≥55°) while no edge loading was observed during standing up, sitting down and knee bending activities. The duration of edge loading increased with increased cup inclination angles and was affected by the cup anteversion angles. Edge loading caused elevated contact pressure at the articulating surface and substantially increased equivalent plastic strain of the polyethylene liner. The present study suggested that correct positioning the component to avoid edge loading that may occur during daily activities is important for MoP THR in clinical practice.     

The effect of cup inclination and wear on the contact mechanics and cement fixation for ultra high molecular weight polyethylene total hip replacements

The present study aimed to investigate individual and combined influences of the cup inclination and wear on the contact mechanics and fixation of a Charnley hip replacement using finite element method. The effects of cup inclination and penetration on the contact mechanics of articulating bearings as well as the stress within the cement and at the bone-cement interface were examined. The maximum contact pressure and the von Mises stress on the cup were reduced by ~30% and ~20% respectively when even a small penetration occurred. However, no large differences were found between different cup penetration depths with regards to either the contact pressure or the von Mises stress. The von Mises stress at the bone-cement interface was predicted almost unaltered with an increased cup inclination angle to 55° for a cup penetration to 4mm. These predictions suggest that the contact mechanics and the cement stress are insensitive to the cup inclination and wear under these normal conditions investigated, therefore explaining the robustness of the Charnley hip implant. An increase in the cup inclination angle to 65°, coupled with a maximum penetration of 4mm, resulted in a large increase in the maximum von Mises stress at the bone-cement interface.     

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.     

髋关节表面置换改良杯的生物力学评价

髋关节表面置换术远期的松动率比全髋关节置换术高,且头杯的松动率较臼杯为高。但髋关节表面置换术具备一些全髋关节假体置换术所没有的优点,如:能保留健康的股骨颈,且尚有全髋关节假体置换术的余地。我们设计了新型的三翼头杯和杆栓杯,简称TC和BC。其中心杆使头杯与残存股骨颈一体化,使假体与残存骨质成为完整受力体系,均匀分散杯下应力。实验采用压力应变值和最大破坏扭矩来评价新头杯与传统头杯的力学稳定性。结果显示,TC综合力学性能最佳,有希望为临床提供一个较理想的头杯。