Contact Mechanics in the Artificial Knee Joint

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) is the material generally used for the articular plate contact surface in artificial knee joints. However, the wear of this material becomes a serious problem during the extended life of the joint. To understand the wear mechanism of the plate during walking and to improve its wear life, the cyclic contact behavior of the plate was analyzed using the constitutive equation for cyclic plasticity, because the UHMWPE is an inelastic material and the plate is subjected to cyclic contact deformation during walking. In this analysis, the two-dimensional plane strain model was employed and the contact behavior of femoral and tibial components was simulated by translating the contact stress distribution, which was calculated from elastoplastic indentation analysis of two components. The posterior cruciate ligament (PCL) retention-type artificial knee joint as the basic analytical model and two other modified contact surface models were analyzed to investigate the effect of the shape of the contact surface on the wear behavior of the plate. As a result, it is clarified that the effect of the stress history, to which the UHMWPE has been subjected, on the wear mechanism of the UHMWPE is significant, that the wear of the plate should occur from both the surface and the subsurface of the plate, and that the wear behavior of the plate is closely related to the shape of the contact surface. The optimal design of the contact surface of the plate is considered using this analysis.