Wear mechanisms of UHMWPE in total joint replacements

Abstract

The wear of ultra-high molecular weight polyethylene (UHMWPE) has become a major focus regarding the long-term clinical performance of total joint replacements. Clinical retrieval analysis has revealed the existence of two distinct wear mechanisms that are operational in both total hip and total knee replacements. While the majority of the wear debris produced from the acetabular component is less than a micron in size and often particulate or fibrous in shape, much larger thin flakelike wear debris is produced from the tibial component. Two theoretical wear models that are based on the scale of intimate asperity interactions are proposed to account for the observed differences in hip and knee wear. Cyclic plastic strain accumulation is identified as the common cause for wear debris generation in both hip and knee replacements. In the case of acetabular cup wear, the scale of plastic deformation is limited to the sites of intimate micro-asperity contacts and the wear rate is defined by a critical strain criterion. In the case of tibial component wear, however, plastic deformation spreads into the subsurface to the site of macro-asperity contacts, and material can be removed by subsurface cracking and delamination. In both cases, the wear rate is strongly affected by the ultimate tensile strength and breaking elongation of the UHMWPE material.