Tribological and surface analysis of 38 mm alumina-as-cast Co-Cr-Mo total hip arthroplasties.

There is currently much discussion over the use of ceramic femoral components against metal acetabular cups, for use in total hip arthroplasty. The current study investigates six hot isostatically pressed alumina femoral heads of 38 mm diameter articulating against six as-cast Co-Cr-Mo metallic acetabular cups. Standard walking-cycle simulator wear testing was carried out to 5 x 10(6) cycles using the Durham Mark II hip wear simulator, and wear was determined gravimetrically. In addition, surface topography, using a non-contacting profilometer, an atomic force microscope, and an optical microscope, was monitored throughout the wear test. The wear of the ceramic heads was found to be undetectable using the current gravimetric method; however, a change in the surface topography was seen, as grain removal on the pole was observed through atomic force microscopy analysis. A biphasic wear pattern was found for the metallic cups, with low wear rates of 1.04 +/- 0.293 mm3/10(6) cycles (mean, +/- 95 per cent confidence interval) and 0.0209 +/- 0.004 mm3/10(6) cycles (mean, +/- 95 per cent confidence interval) for running-in and steady state wear phases respectively. Frictional measurement revealed that the joints were tending towards full fluid-film lubrication in parts of the walking cycle. The results show that the combination of hot isostatically pressed alumina and as-cast Co-Cr-Mo is a promising alternative for total hip arthroplasties.