Designing for Crosslinked UHMWPE Implants: Clinical Consequences of Stress Concentrations

Ultrahigh molecular weight polyethylene (UHMWPE) remains the polymer bearing of choice for total joint replacements (TJR) [1]. However, the long-term performance of this polymer has been limited by in vivo wear: UHMWPE wear debris generated in the joint space can travel into the periprosthetic bone, initiating osteolysis and implant loosening [2]. Crosslinked UHMWPE (through ionizing radiation) has demonstrated increased wear resistance [3], but at the cost of reduced fatigue crack propagation and fracture resistance [4]. Additionally, radiation processes can release free radicals which, when not eliminated through thermal treatment, can increase UHMWPE susceptibility to oxidation and mechanical embrittlement [5]. Such tradeoffs present clinical concerns when implant designs incorporate stress concentrations that experience elevated stresses under loading. These compromises are evaluated through the failure analysis of several crosslinked UHMWPE retrievals that fractured in vivo.