Effects of fine microstructures and precipitates of laser-sintered Co-28Cr-6Mo alloy femoral components on wear rate of UHMWPE inserts in a knee joint simulator.

To develop a new manufacturing process for total knee arthroplasty (TKA) femoral components, we investigated the effects of fine microstructures and precipitates on the wear rate of ultrahigh-molecular-weight polyethylene (UHMWPE) inserts against a laser-sintered Co-28Cr-6Mo alloy femoral component measured using a knee joint simulator. The tensile and fatigue strengths of the laser-sintered Co-28Cr-6Mo alloy were higher than those of cast Co-28Cr-6Mo and aged Zr-2.5Nb alloys. The laser-sintered Co-28Cr-6Mo alloy had finer microstructures and precipitates of the pi (π)-phase [(Cr, Mo)12Co8(C, N)4; lattice constants: a = b = c = 0.636 nm] in the grains and grain boundaries. The volumetric wear rate (7.16 ± 1.9 mm3/million cycles) of conventional UHMWPE (CPE, non-highly crosslinked) against a laser-sintered Co-28Cr-6Mo femoral component was lower than that of previously reported CPE inserts with Genesis Ⅱ TKA devices. Since the effect of precipitates of the π-phase on the increase in the wear rate was negligible, laser sintering is a promising new manufacturing technology for femoral components.