Type of motion and lubricant in wear simulation of polyethylene acetabularcup

The wear of ultra-high molecular weight polyethylene, the most commonly use d bearing material in prosthetic joints, is often substantial, posing a sig nificant clinical problem. For a long time, there has been a need for simpl e but still realistic wear test devices for prosthetic joint materials. The wear factors produced by earlier reciprocating and unidirectionally rotati ng wear test devices for polyethylene are typically two orders of magnitude too low, both in water and in serum lubrication. Wear is negligible even u nder multidirectional motion in water. A twelve-station, circularly transla ting pin-on-disc (CTPOD) device and a modification of the established biaxi al rocking motion hip joint simulator were built. With these simple and ine xpensive devices, and with the established three-axis hip joint simulator, realistic wear simulation was achieved. This was due to serum lubrication a nd to the fact that the direction of sliding constantly changed relative to the polyethylene specimen. The type and magnitude of load was found to be less important. The CTPOD tests showed that the subsurface brittle region, which results from gamma irradiation sterilization of polyethylene in air, has poor wear resistance. Phospholipid and say protein lubrication resulted in unrealistic wear. The introduction of devices like CTPOD may boost wear studies, rendering them feasible without heavy investment.