POLYETHYLENE WEAR PERFORMANCE OF OXIDIZED ZIRCONIUM AND COBALT-CHROMIUM KNEE COMPONENTS UNDER ABRASIVE CONDITIONS

The surfaces of retrieved cobalt-chromium (CoCr) total knee arthroplasty femoral components show evidence of roughening ( Fig. 1 ) 1-3. In vitro studies have shown that scratches on the hard counterface, particularly those at an angle to the direction of motion, can increase wear of ultra-high molecular weight polyethylene 4-10. An alternative material, oxidized zirconium (OxZr), was developed to provide an improvement over CoCr in resistance to roughening, frictional behavior, and biocompatibility 11-16. Previous knee simulator testing under clean conditions (without intentional addition of abrasives) demonstrated that articulation with OxZr femoral components resulted in rates of wear of the ultra-high molecular weight polyethylene that were more than sixfold lower than those obtained with CoCr femoral components 17. Because femoral components roughen clinically in a way that can increase wear of the ultra-high molecular weight polyethylene insert, simulator testing under abrasive conditions also was needed to better characterize the performance of the femoral component material. Previously, adding abrasives into the test media during simulation did not produce relevant conditions, so a technique was developed to roughen the surface of the femoral components by tumbling them with alumina powder and plastic cones before simulator testing 18. In the present study, we compared the wear performance of CoCr and OxZr in an anatomic knee simulator under these abrasive conditions. Fig. 1: Hard particles scratch cobalt-chromium surfaces under clinical conditions, plowing up adjacent peaks that can increase abrasive wear of polyethylene, as seen on this interferometer image of a retrieved clinical specimen 1,2. The wear performance of three cast CoCr (ASTM F75) and three OxZr (Oxinium) femoral components were compared. Femoral components were tumbled with 25 μm alumina powder and plastic cone media in a centrifugal finishing barrel 18. The inserts …