Wear, oxidation and mechanical properties of a sequentially irradiated and annealed UHMWPE in total joint replacement

Ultra high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in joint replacement prostheses for over 40 years. Recently, highly crosslinked UHMWPE (HXPE) materials were introduced based on the finding that crosslinking reduces wear. These first generation HXPE materials were produced by irradiation followed by heating below the melting temperature (annealing) or above the melting temperature (remelting). Both classes of HXPE material have demonstrated greatly reduced wear. However, remelted HXPE materials have reduced fatigue strength while annealed HXPE materials may oxidize when exposed to oxygen. A second generation HXPE material was produced using a sequential irradiation and annealing process (SXL). SXL materials have crosslinking levels equivalent to those of first generation HXPE materials, have fatigue and mechanical strength characteristics of first generation annealed HXPE material and have an oxidation resistance equivalent to that of virgin (unprocessed) UHMWPE. This combination of properties makes SXL HXPE a preferred material for bearing surfaces of joint prostheses.