Influence of simulator kinematics on the wear of metal-on-metal hip prostheses

There is now considerable interest in metal-on-metal bearings for hip prost heses. Extremely low wear rates (0.1 mm(3)/10(6) cycles) have been reported in some simulator studies, while in vivo studies, although still very low, have shown wear rates of the order of 1 mm(3)/10(6) cycles. The aim of thi s study was to compare wear rates of metal-on-metal bearings in two hip sim ulators with different kinematic inputs. In the simulator with three indepe ndent input motions which produced an open elliptical wear path with a low level of eccentricity, the wear rates were very low as recorded previously in other simulators. In the simulator with two input motions which produced an open elliptical wear path with greater eccentricity the wear rate was a t least ten times higher and closer to clinical values. The motion and kine matic conditions in the contact are critical determinants of wear in metal- on-metal bearings.