Optimum Design of Knee Prostheses with High Performance Similar to Natural Knee Joints

本研究的目的是发展一种优化设计的方法，使膝关节假体具有与自然膝关节相似的高性能。我们的主要目标是建立膝关节假体中的流体膜形成。膝关节接触条件的三维分析首先，由于我们的膝关节假体模型具有与自然关节相似的几何形状，因此，我们将基于CAD理论的三维几何分析应用于自然膝关节。利用该数学表达式得到了弯曲关节面在屈曲和伸展状态下的接触点和承载特性，并采用二次三维光弹性冻结法研究了伸展状态下的接触应力分布。结果表明，关节软骨和半月板能显著降低软骨下骨的接触应力.膝关节模拟试验为评价膝关节假体在行走状态下的液膜形成情况，研制了膝关节模拟装置，并用于测量股骨和胫骨部件之间的接触电阻和摩擦力。在一个膝关节假体与弹性胫骨组件，弹性流体动力学膜相当大的形成，即使在加载的立场阶段，而在一个假体与聚乙烯胫骨之一，轻微的流体膜形成后，观察到脚跟罢工，除了在摆动阶段。在前者中，膜厚度在站立阶段期间减小，并且通常在脚趾离地之前的峰值载荷处变得最小，并且在摆动阶段期间恢复到先前的水平。实验结果表明，在适当的润滑条件下，具有柔顺性人工软骨的膝关节假体能够改善流体膜的形成。

The object of this research is to develop the approaches for the optimum design for knee prostheses with high performance similar to natural knee joints. What we are aiming principally at is to establish fluid film formation in knee prostheses.The following methods were carried out.1. Three-dimensional analysis for the contact conditions in knee jointsFirsty, the three-dimensional geometric analysis based on the CAD theory was applied to natural knee joints, since our trial knee prosthesis model has similar geometry to the natural joint. The contact points and load-carrying characteristics in the flexed and extended conditions were obtained by using this mathematical expression for curved articular surfaces.Secondary, three-dimensional photoelastic freezing method was applied to investigate the contact stress distribution in the extended position. It was shown that the articular cartilage and meniscus remarkably reduced the contact stresses in the subchondral bones.2. Knee joint simulator testTo evaluate the fluid film formation in knee prostheses under walking condition, the knee joint simulator was developed and used for the measurement of electric contact resistance and friction between femoral and tibial components. In a knee prosthesis with an elastomeric tibial component, elastohydrodynamic film was considerably formed even during the loading stance phase, whereas in a prosthesis with a polyethylene tibial one, slight fluid film formation was observed only immediately after the heel strike except during the swing phase. In the former, the film thickness decreases during the stance phase and generally becomes minimum at the peak load just before the toe off, and recovers to the previous level during the swing phase. It is suggested from the experimental results that the knee prosthesis with complient artificial cartilage is capable of improving the fluid film formation with adequate lubricants.