SIMULATED KNEE WEAR WITH COBALT-CHROMIUM AND OXIDIZED ZIRCONIUM KNEE FEMORAL COMPONENTS

A knee simulator that mimics the plowing/rolling wear mechanisms of th e knee was used to compare wear properties of cobalt chromium and oxid ized zirconium femoral components. The simulator flexes and extends th e knee so that the femoral component travels from 0 degrees to 30 degr ees while applying axial loads from 130 to 1300 lb. Three oxidized zir conium and 3 cobalt chromium femoral components were tested with 10-mm tibial polyethylene components. The oxidized zirconium femoral compon ents caused significantly less ultra high molecular weight polyethylen e wear than cobalt chromium femoral components. Tibial inserts that we re articulated against the cobalt chromium components had evidence of scratching, burnishing, and delamination, but none of the surfaces tha t were articulated against oxidized zirconium components had evidence of delamination. Cobalt chromium surface roughness significantly incre ased during the 2,000,000 cycle test, but oxidized zirconium surface r oughness was not affected. Polyethylene wear was correlated to a signi ficant degree with the surface roughness of the femoral components. Th e improved wear characteristics of the ceramic articular surfaces can be explained by the wettability of the ceramic surface, which minimize d adhesive wear, and the resistance of the hard, ceramic surface to ro ughening.