Alumina hip joints characterized by run‐in wear and steady‐state wear to 14 million cycles in hip‐simulator model

The biphasic wear performance (run‐in; steady‐state phase) of 28‐mm alumina‐alumina hip implants was studied by hip simulator methods using bovine serum as the lubricant. The Biolox™ implants were run to 5.7 million cycles and Bioceram™ implants to 14.4 million cycles (Mc). Wear with all‐alumina total hip replacements (THR) first showed a high wear rate of the order 1.2 mm 3 /Mc, lasting approximately 0.17 Mc. Overall to 0.7 Mc, the run‐in phase appeared curvilinear but could be described by a linear phase averaging 0.3 mm 3 /Mc. From 0.7 to 1 Mc duration, the wear trend transitioned into a steady‐state phase. Wear rates from 1 to 14 Mc were of the order 0.02 mm 3 /Mc. Surface contamination from the serum lubricant resulted in cyclic weight fluctuations of the order 0.2 mg. The transition from average run‐in to steady‐state phase represented a wear reduction of 13‐fold. Comparing the steady‐state wear value to that in standard 28‐mm UHMWPE CUPS approaching 75 mm 3 /year, there was clearly a three‐orders‐of‐magnitude wear superiority in favor of ceramic cups. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 523–532, 2004