Wear phenomena in knee prostheses and their finite element analyses

The wear phenomenon of ultra-high molecular weight polyethylene (UHMWPE) in knee and hip prostheses is one of the major restriction factors on the longevity of these implants. Despite quite a number of studies on the wear of UHMWPE, the wear mechanism is not clear yet. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. In this study, observation of wear characteristics of UHMWPE tibial inserts in retrieved knee prostheses, elasto-plastic contact analyses of simplified artificial knee joint models using finite element method (FEM), elasto-plastic contact analysis of a UHMWPE tibial insert based on geometrical measurement from a retrieved knee prosthesis were performed to investigate the factors influencing the wear of UHMWPE. The results of this study suggest that lack of polyethylene thickness, cold flow into screw holes, high contact stresses, low degree of conformity, presence of fusion defects in polyethylene, metallic third-body wear particles, maximum plastic strain below the surface, and slip ratio in knee prosthesis have a significant effect on the wear of UHMWPE. These are therefore significant factors influencing the wear mechanism of UHMWPE.