UHMWPE wear against roughened oxidized zirconium and CoCr femoral knee components during force-controlled simulation

Increased femoral knee component surface roughness is clinically and experimentally correlated with increased ultra-high molecular weight polyethylene (UHMWPE) wear rates. Ceramic-surfaced femoral components have increased scratch resistant surfaces, which offer the potential to reduce UHMWPE wear rates. In this study, oxidized zirconium (OxZr) and cobalt chromium (CoCr) femoral components were first subjected to a standardized roughening protocol. An in vitro total knee replacement (TKR) wear study was then conducted using conventional UHMWPE to quantify the effect of femoral surface roughening on TKR kinematic, kinetic and wear performance over time. An Instron/Stanmore force-controlled knee simulator was used to conduct a 5 million cycle wear simulation using ISO-14243 walking cycles. During the pre-test roughening procedure, the OxZr component surfaces resisted third body scratching better than the CoCr component surfaces. During wear testing, the roughened OxZr femoral components generated 82% less wear when compared to the roughened CoCr femoral components. Significant reductions in TKR ranges of motion were found over time despite linear wear rates. This study demonstrates the potential of OxZr femoral knee components for reducing polyethylene wear in vivo when under potentially abrasive conditions and offers new insights into the effects of wear on TKR kinematics over time.