Plasticity-induced damage layer is a precursor to wear in radiation-cross-linked UHMWPE acetabular components for total hip replacement

The mechanism for the improved wear resistance of cross-linked ultra-high-m olecular-weight polyethylene (UHMWPE) remains unclear. This study investiga ted the effect of cross-linking achieved by gamma irradiation in nitrogen o n the tribologic, mechanical, and morphologic properties of UHMWPE. The goa l of this study was to relate UHMWPE properties to the wear mechanism in ac etabular-bearing inserts. Wear simulation of acetabular liners was followed by detailed characterization of the mechanical behavior and crystalline mo rphology at the articulating surface. The wear rate was determined to be di rectly related to the ductility, toughness, and strain-hardening behavior o f the UHMWPE. The concept of a plasticity-induced damage layer is introduce d to explain the near-surface orientation of the crystalline lamellae obser ved in the wear-tested acetabular liners. Cross-linking reduces abrasive we ar of acetabular components by substantially reducing-but not eliminating-t he plasticity-induced damage layer that precedes abrasive wear.