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Materials and Methods:Three component assemblies of LEGION cruciate retaining (CR) OxZr femoral components,7.5-XLPE tibial inserts were tested on an AMTI knee simulator under displacement control at 1Hz frequency as described previously. 2 The tibial inserts were manufactured from compressionmolded GUR 1020 UHMWPE, radiation crosslinked to 7.5 Mrad dose, remelted to extinguishfree radicals, and sterilized by EtO. The wear test was conducted for 45 Mcycle, which wasconsidered to be a conservative estimate for the amount of cycles that would occur during 30years of typical in-vivo use based on the relationship between patient age and the number ofloading cycles as reported in the literature. 6-8Results:The predominant wear feature on the 7.5-XLPE inserts was burnishing. There were no signs offatigue wear or delamination. The mean volumetric wear rate (± SD) of the 7.5-XLPE insertsarticulating against OxZr femoral components for 45 Mcycle was 0.58±0.17 mm 3 /Mcycle.In a previous wear test under substantially identical conditions for 5 Mcycle simulatingapproximately 3 years of use, the mean volumetric wear rate of CoCr and virgin UHMWPE(CPE) couples was 23.4±2.4 mm 3 /Mcycle. 2 The mean volumetric wear rate of the OxZr/7.5-XLPE couples was approximately 98% lower compared to the CoCr/CPE couples (p