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Effectiveness of Ceramic Femoral Components on Reduction in Tibial Polyethylene Wear: A Simulator Study

We investigated the surface properties and wear performances of a standard cobalt-chromium (Co-Cr) alloy and 2 kinds of ceramic femoral components (alumina and zirconia) in tibial polyethylene inserts tested in a knee simulator. Hardness, wettability (lubricity), and presimulator and postsimulator test roughness values of the component surfaces were measured for each material. The simulator was run up to 5.0 million cycles using gait kinematics to determine the wear rate of the tibial polyethylene against each group. Vickers hardness values of the femoral components made of Co-Cr, alumina, and zirconia averaged 339 ± 14.8, 1869 ± 40.6, and 1382 ± 15.8, respectively. Contact angles with distilled water (in degrees) of the femoral components made of Co-Cr, alumina, and zirconia averaged 76.9 ± 3.2, 34.9 ± 1.5, and 73.5 ± 0.8, respectively. The aggregate volumetric wear rate for the Co-Cr femoral components was 3.35 ± 1.33 mm3 per million cycle; those of the alumina and zirconia femoral components were 0.15 ± 0.08 and 0.57 ± 0.18 mm3/M, respectively. Differences between the wear rate of the Co-Cr and ceramic femoral components were statistically significant (n = 3; P < 0.01). The posttest roughness values of ceramic femoral condyles were significantly smaller than that of the Co-Cr condyles. The reduction in the tibial polyethylene wear was likely attributable to the greater wettability and resistance to roughening of the ceramic components.