Cushion form bearings for total knee joint replacement. Part 1: Design,friction and lubrication.

Cushion knee prostheses have been designed and constructed that produce approximately equal initial contact areas and theoretical film thicknesses compared with a conventional UHMWPE (ultra-high molecular weight polyethylene) joint. These compliant bearings had a flat tibial component which imposed fewer biomechanical constraints and allowed a greater range of movement. Friction experiments have been carried out on a pendulum simulator apparatus. The results showed that the cushion knee joints operated just within the mixed lubrication regime, but that they benefited from a substantial measure of fluid film lubrication. Microelastohydrodynamic lubrication was effective in preserving low friction and thin but effective lubricating films.