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

Abstract

The potential for bone and poly(methyl methacrylate) (PMMA) debris to initiate wear on ASTM-F75 and ASTM-F799 CoCrMo alloys articulating against ultrahigh molecular weight polyethylene (UHMWPE) was investigated. Third-body wear particles of bone and PMMA bone cement (with and without the radiopacifier, barium sulfate) were introduced between CoCrMo and UHMWPE in a reciprocating sliding wear test. A scanning electron microscope and a white light interference surface profilometer were used to study the surface damage and quantify the surface roughnesses of the worn alloys. The CoCrMo alloys, which 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 or PMMA debris. Severe scratches were generated within 2700 cycles (94.5-m sliding distance) on the alloy's surface. Ploughing was the major wear mechanism. Carbides in the F75 alloy surface appeared to be unaffected by the debris. A quantitative study was performed on the surface roughness (average roughness, R(a), and root mean square roughness, RMS) of the alloy after wear 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 the specimens tested with the PMMA and bone particles were significantly rougher 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 caused by defects and impurities in the UHMWPE.