Highly crosslinked polyethylenes in hip replacements: Improved wear performance or paradox?

The lubrication and wear of artificial joints are important issues for their longevity. Bone loss caused by the biological response (osteolysis) to the wear debris leads to implant loosening and eventual failure of the device. Various studies have shown that the size, shape, and the number of particles are important factors in the osteolytic response to wear debris. It has been demonstrated that both submicron-size particles and long fibrils can stimulate macrophage responses. This paper examines the clinical and laboratory data on highly crosslinked polyethylene (XLPE) regarding implant wear and particulate debris. In simulator studies, total hip replacements have shown greatly reduced wear with XLPE cups compared with conventional polyethylene (PE) and short-term clinical studies of XLPE have now also shown reduced levels of wear. However, simulator studies have also demonstrated that adverse wear conditions can partially or completely negate the wear advantage of XLPE. Additionally, it has been shown that the XLPE debris particles are smaller than conventional PE. In a paradoxical manner, the decreased wear rate of XLPE should decrease the osteolytic potential, but the decreased debris size may have the potential to increase the biological activity. Therefore, the long-term clinical performance of XLPE is not clear at this time. Long-term clinical follow-ups will be needed to determine the actual benefit of XLPE in patients.