Second-generation Annealed Highly Cross-linked Polyethylene Exhibits Low Wear

Abstract

Compared with conventional polyethylene, first-generation highly cross-linked polyethylenes have low wear, but controversy exists regarding their reduced mechanical strength and/or retained free radicals. Second-generation highly cross-linked polyethylenes have been developed to reduce wear, maintain mechanical strength, and have oxidative resistance, but it is unclear whether they do so. The primary objective of this study therefore was to determine if a second-generation annealed material has low linear wear at 5years followup. Secondary objectives were to evaluate for overall survivorship, implant fixation, osteolysis, and effect of socket inclination on wear. In a multicenter prospective study, we radiographically evaluated 155 patients (167 hips) at 3years, 124 patients (132 hips) at 4years, and 46 patients (51 hips) at 5years. The linear head penetration rate was measured at 6weeks, 1year, and yearly through 5years. The head penetration per year after the first year of bedding-in was 0.024mm per year at 3years, 0.020mm per year at 4years, and 0.008mm per year at 5years. The average wear rate over 5years was 0.015mm per year and represents a 58% improvement over a first-generation annealed highly cross-linked polyethylene. The Kaplan-Meier survivorship (revision for any reason) was 97.8%. We revised no hip for bearing surface failure and observed no osteolysis. Socket inclination did not affect linear wear. These data suggest the linear wear rate for a second-generation annealed highly cross-linked polyethylene is no greater than that for historic controls of first-generation highly cross-linked polyethylenes, and no untoward complications were encountered with this new material. Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.