Highly cross-linked formulations of ultrahigh-molecular-weight polyethylene (XLPE) offer exceptional wear resistance for total joint arthroplasty but are offset with a reduction in postyield and fatigue fracture properties in comparison to conventional ultrahigh-molecular-weight polyethylene (UHMWPE). Oxidation resistance is also an important property for the longevity of total joint replacements (TJRs) as formulations of UHMWPE or XLPE utilizing radiation methods are susceptible to free radical generation and subsequent embrittlement. The balance of oxidation, wear, and fracture properties is an enduring concern for orthopedic polymers used as the bearing surface in total joint arthroplasty. Optimization of material properties is further challenged in designs that make use of locking mechanisms, notches, or other stress concentrations that can render the polymer susceptible to fracture due to elevated local stresses. Clinical complications involving impingements, dislocations, or other biomechanical overloads can exacerbate stresses and negate benefits of improved wear resistance provided by XLPE. This work examines trade-offs that factor into the use of XLPE in TJR implants.

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.