The effect of kinematic conditions on the wear of ultra-high molecular weight polyethylene (UHMWPE) in orthopaedic bearing applications

It is known that wear mechanisms differ between the ultra-high molecular we ight polyethylene (UHMWPE) components of total hip replacement (THR) and to tal knee replacement (TKR). The difference in relative contact position or 'kinematic conditions of contact' between the metal and polymer components is thought to contribute to the contrast in observed wear mechanisms. A reciprocating wear tester was used to evaluate three basic kinematic cont act conditions: sliding, in which the relative contact position on the poly mer remains stationary; gliding, where the contact position on the polymer reciprocates: and rolling, where the contact position on the polymer varies and the relative velocities of both components are equal. All static load tests used cast Co-Cr alloy and irradiated Chirulen(R) UHMW PE in a 37 degreesC environment lubricated with bovine serum albumin. UHMWP E test sample wear was measured gravimetrically at intervals of 600 000 cyc les. The results indicated a difference in wear factor (volume lost due to wear per unit load per unit sliding distance) between the three groups with varying relative motion. The study indicates that screening tests which ev aluate wear properties of new materials for total joint replacement should reflect the different kinematic contact conditions.