Aspherical Femoral Head with Highly Cross-Linked Ultra-High Molecular Weight Polyethylene Surface Cracking

Hip simulator and early clinical studies of highly cross-linked ultra-high molecular weight polyethylene have demonstrated less wear and less femoral head penetration when compared with conventional ultra-high molecular weight polyethylene1-6. However, cross-linking also alters some of the mechanical properties of ultra-high molecular weight polyethylene, including its ultimate tensile strength, strain to failure, fracture toughness, and fatigue crack propagation resistance7-9. Analyses of early retrieved highly cross-linked components have shown initiation of surface cracking, which is possibly related to the decrease in ductility caused by cross-linking10. A reduction in ductility, fracture, and fatigue properties is the hallmark of material embrittlement. Accordingly, newer so-called second-generation highly cross-linked polyethylenes have been developed in an effort to better retain the desirable mechanical properties of conventional ultra-high molecular weight polyethylene as well as the benefits of cross-linking11.