Different Loading and Motion Applied on Hip Simulators Affects the Lubrication of Metal-on-Metal Hip Implants

The transient elastohydrodynamic lubrication for metal-on-metal (MOM) total hip replacement was numerically solved under three gait loading and motion patterns, according to Leeds Mk I hip simulator, Leeds ProSim and ISO standard, respectively. The Reynolds equation for pressure calculation was solved in spherical coordinate system using the multi-grid method and the elastic deformation of both acetabular cup and femoral head was obtained by spherical FFT technique. Full numerical solutions of EHL were obtained including the pressure and film thickness distribution, for MOM hip replacement under the three gait patterns. Large variations in the film thickness were observed for different patterns, especially when the three dimensional load applied on. For example, the film thickness was significantly increased using Leeds Mk I pattern. This may result in large difference of hip simulator wear testing.