In Vivo Oxidation of γ-Barrier–Sterilized Ultra–High-Molecular-Weight Polyethylene Bearings

γ-Barrier packaging is shown to be effective in preventing oxidation of polyethylene during shelf storage and in addressing the problem of early fatigue failure seen in γ-air–sterilized bearings with long shelf-storage before implantation. The series of γ-barrier retrievals studied suggests that oxidation occurs in the body via the same mechanism as seen in γ-air–sterilized bearings. A critical oxidation level is identified above which polyethylene bearings are susceptible to fatigue damage after sufficient cycles of use. Although critical oxidation was not reached in the majority of the retrieved γ-barrier bearings studied, in vivo oxidation appears to follow an exponential increase with time. The result of in vivo oxidation is expected to be loss of mechanical properties, and susceptibility of polyethylene bearings to eventual fatigue failure.