2006 Otto Aufranc Award Paper: significance of in vivo degradation for polyethylene in total hip arthroplasty.

Our research group developed an implant retrieval program to study in vivo degradation of polyethylene. We now have evidence to support our hypothesis that degradation of radiation-sterilized polyethylene occurs in the body for not only historical gamma air sterilized liners, but also for conventional gamma inert sterilized (ArCom) and annealed highly crosslinked polyethylene (Crossfire) liners as well. Our research has also led to the discovery that the most severe manifestations of in vivo oxidation typically occur in regions of the liner experiencing minimal wear, such as the rim of the component, where the body fluids (containing oxidizing species) have access to the polyethylene. Our data from historical, ArCom, and Crossfire retrievals all point to a similar scenario in which the femoral head limits the in vivo oxidation of polyethylene at the bearing surface. Consequently, provided rim impingement does not occur, and the polyethylene locking mechanisms remain relatively isolated from oxidizing fluid, in vivo oxidation does not seem to be clinically important in the first 10 years of implantation for conventional gamma sterilized polyethylene. We conclude that in vivo degradation should be included among the list of potential long-term failure modes for modular polyethylene components for total hip arthroplasty.