Third-body wear of cobalt-chromium-molybdenum implant alloys initiated by bone and poly(methyl methacrylate) particles

The potential for bone and poly(methyl methacrylate) (PMMA) debris to initi ate wear on ASTM-F75 and ASTM-F799 CoCrMo alloys articulating against ultra high molecular weight polyethylene (UHMWPE) was investigated. Third-body we ar particles of bone and PMMA bone cement (with and without the radiopacifi er, barium sulfate) were introduced between CoCrMo and UHMWPE in a reciproc ating sliding wear test. A scanning electron microscope and a white light i nterference surface profilometer were used to study the surface damage and quantify the surface roughnesses of the worn alloys. The CoCrMo alloys, whi ch are widely used as the femoral components in total artificial knees and hips, showed surface damage as the result of wear in the presence of bone o r PMMA debris. Severe scratches were generated within 2700 cycles (94.5-m s liding distance) on the alloy's surface. Ploughing was the major wear mecha nism. Carbides in the F75 alloy surface appeared to be unaffected by the de bris. A quantitative study was performed on the surface roughness (average roughness, R-a, and root mean square roughness, RMS) of the alloy after wea r testing. A nonparametric Wilcoxon rank sum test of wear severity (R-a and RMS) was performed based on the surface roughness data. The surfaces of th e specimens tested with the PMMA and bone particles were significantly roug her than those of the controls (p < 0.01). Small scratches also occurred on some of the control specimen surfaces and may have been second-body wear c aused by defects and impurities in the UHMWPE. (C) 2000 John Wiley & Sons, Inc.