Conventional ultra-high molecular weight polyethylene: a gold standard of sorts

Data from a series of four recent studies showed that conventional polyethylene liners sterilized by gamma irradiation in air and coupled with second-generation acetabular components outperformed first-generation components with consistent average wear behavior below 0.1 mm/yr. It was found that liners sterilized by gamma irradiation in air outperformed liners sterilized by gas plasma, indicating that cross-linking induced by gamma irradiation sterilization, even if the component is radiated in an oxygen environment, is essential for keeping wear rates low. No negative clinical effects were found on wear for conventional polyethylene sterilized by gamma irradiation in air with a shelf life up to 3 years (r2 = 0.04, P = 0.60). Finally, 16-year temporal wear patterns for gamma irradiation in air sterilized components demonstrated no significant changes in wear rates over time, indicating that gamma irradiation sterilized liners with short shelf lives will not likely experience late increases in wear because of continued in vivo oxidation of the polyethylene. From these studies it was determined that standardized radiographic methods, optimal radiographs, serial measurements, and minimum 4-year follow-up are essential for reliable wear data. More specifically, it was concluded that a conventional ultra-high molecular weight polyethylene liner gamma irradiation sterilized in air with a shelf life less than 3 years, coupled with a second-generation cup, performs well in vivo and is unlikely to experience late increases in wear. Because no comparable in vivo data will be available for new cross-linked polyethylene materials for several years, conventional gamma irradiated polyethylene can be considered the industry's current gold standard for wear performance comparisons.