8-YEAR PROSPECTIVE RANDOMIZED COMPARISON BETWEEN A CROSSLINKED AND CONVENTIONAL POLYETHYLENE IN TOTAL HIP ARTHROPLASTY.

Abstract

Introduction: Simulator wear studies of crosslinked polyethylene (PE) show promising results but long-term clinical investigations addressing concerns about in-vivo aging, PE deterioration, late wear and osteolysis are scarce. This study reports the longest published follow-up comparing conventional to crosslinked PE.

Methods: Crosslinked PE (Stryker Duration: 3MRad gamma irradiation in N2, post-irradiation annealed) was compared to conventional PE (3MRad gamma irradiation in air) in a MTS hip simulator and a prospective randomized clinical study involving 48 THA patients (Stryker ABG-II stem and cup, 28mm ball diameter) with a mean follow-up of 8 (7–9) years. Patients were followed-up annually using the HHS, radiographs and wear measurements applying a digital Livermore method.

Results: Forty patients (23 conventional, 17 Duration) were left for analysis (five premature deaths, 3 loss to follow-up). Both groups were statistically non-different (p> 0.1) regarding age (63.9 years), gender, BMI, stem size, cup size, cup inclination and liner thickness leaving the insert material as the only variable. Pre-op HHS (39.7) and post-op HHS (93.7) were also not different.

At 8-years the wear rate was significantly (p< 0.01) lower for Duration [0.088 ± 0.03 mm/yr (0.02–0.14)] than conventional PE [0.142 ± 0.07 mm/yr (0.05–0.31)]. This reduction (−38%) compared well to the simulator (−45%) and did not change over time (−33% at 5-years). Radiolucencies and signs of osteolysis were also less in the Duration group (n.s.).

Discussion: In-vivo wear reduction by crosslinked PE is similar as predicted by the simulator and does not seem to deteriorate over time. Concerns over higher levels of residual free radicals after annealing instead of remelting do not seem justified. The lower wear correlated with reduced radiographic signs of osteolysis which may result in superior survival at longer follow-up.