351 patients (701 knees) with osteoarthritis underwent simultaneous bilateral total knee replacement (TKR), in which each knee was randomized to receive an oxidised zirconium (OxZr) or a cobalt-chrome (CoCr) femoral component. After a mean of 7.5 years, there was no significant difference between the two groups for mean weight, size, and shape of the aspirated wear particles. The two groups also did not differ in pain, function ratings, range of movement, and satisfaction with treatment. Since the OxZr component costs more than the CoCr component, it can be concluded that the CoCr femoral component is most suitable for patients with osteoarthritis undergoing TKR following this mid-term assessment.