HIGHLY CROSS-LINKED POLYETHYLENE IN TOTAL HIP REPLACEMENT: PROS AND CONS

Abstract

Summary: Highly crosslinked polyethylenes have now been in use for more than 5 years clinically. To date, clinical studies have supported the in vitro studies demonstrating a statically significant reduction in wear. There remains some ongoing concerns as it relates to the mechanical properties of the polyethylene which may limit its use in certain situations. In general unsupported polyethylene should be avoided as there is a risk for fracture regardless of whether the material is highly crosslinked or not.

Abstract: Highly crosslinked polyethylenes have been developed by several manufacturers and have been released to the market. In vitro studies have demonstrated several important factors. First, there is a relationship between radiation dose and wear reduction. As the radiation dose increases, the wear of the material decreases. This begins to plateau at approximately 10 mrads rounds of radiation. Secondly, studies that are available suggest that highly crosslinked polyethylenes are relatively insensitive to femoral head size. This potentially allows the surgeon to use large femoral heads increasing hip stability and reducing postoperative dissipation while at the same time not comprising wear. Thirdly, radiation negatively affects the mechanical properties of the material. However, it is important to remember that all materials implanted meets industry guidelines for polyethylene and its mechanical properties. There have been several clinical studies looking at different highly crosslinked polyethylenes. It’s important to remember that these materials are manufactured using different techniques and may perform differently over time. Thus, ongoing studies evaluating the different products that have been released to the market are important and need to be continued as it’s quite possible that all materials may not behave the same. The good news is that to date, all clinical studies have demonstrated statically significant improvement in wear over a relatively short time period. There have been some fractures of polyethylene liners. Analysis of these cases suggests that these fractures are more related to implant position and loading of unsupported polyethylene than they are related to the mechanical properties of the material.