Therapeutic study, Level III (retrospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Background Highly cross-linked polyethylene (HXLPE), created by disrupting the molecular structure of polyethylene, then through the application of heat, encourages creation of new cross-links in the process, resulting in a material with improved wear resistance. The impetuses for this new technology were the unsatisfactory wear properties and subsequent osteolysis of noncross-linked polyethylene. A 72% reduction in wear using highly crosslinked polyethylenes (HXLPE) compared with conventional polyethylene at 5 years was described previously. The longest term followup studies on HXLPE range from 2 to 6 years. Questions/purposes We therefore addressed the following questions: (1) Does the improvement in wear observed at the earlier followup continue to 7 to 10 years? (2) What is the incidence of osteolysis in this group of patients and in the control group? Methods We retrospectively reviewed 38 prospectively followed patients who had 42 hips with an annealed HXLPE who were followed a minimum of 7 years (average, 8.6 years; SD = 1; range, 7-10.3 years). Wear and osteolysis were compared with those of a control group of 39 patients (40 hips) from a US Investigational Device Exemption (IDE) prospective, randomized study begun in 1996 with conventional polyethylene and followed for a minimum of 6 years (average, 7.5 years; SD = 1.1; range, 6-10.2 years). Linear head penetration was measured from AP radiographs at early, 1-year, 5-year, and most recent followups. Results At the average followup, annual linear wear was 0.031 mm (SD = 0.014) for the HXLPE and 0.141 mm (SD = 0.080) for the control group, a 78% reduction. No mechanical failure of the polyethylene was noted in either group. Incidence of osteolysis was 50% in the control group (all lesions confined to proximal Gruen Zones 1 and 7) compared with no cases in the investigational group. Conclusions We observed an improvement in wear and no mechanical failures with this annealed material.

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BackgroundPolyethylene wear-induced osteolysis is a major cause of implant loosening in total hip arthroplasty. New crosslinked polyethylenes are presumed to give lower wear rates, but no long-term clinical results are available yet.Patients and methods We compared basic material characteristics and MTS hip joint simulator wear rates of a crosslinked polyethylene (Duration) to those of conventional polyethylene. In a randomized double-blind 5-year clinical follow-up study, 133 hips (67 conventional, 66 Duration) in 127 patients were followed-up for an average of 5 (3-6) years. Wear rates were measured using a computer-based edge detection method. The radiographic appearances of wear-related phenomena were recorded.Results The Duration polyethylene showed a significantly lower in-vitro wear rate in the simulator study (mean 22 (SD 2.3) vs. 40 (SD 1.5) mm3/106 cycles). Also, the in-vivo wear was lower for Duration (mean 0.083 (SD 0.056) mm/year) than for conventional polyethylene (mean 0.123 (SD 0.082) mm/year). All radiographic signs of osteolysis were less frequent in the Duration group.Interpretation Our study has given a substantial body of evidence-from lower wear rates, less frequent signs of osteolysis, and higher survival rates after a mean follow-up of 5 years-that Duration provides better clinical outcomes than conventional polyethylene.