HIGHLY CROSSLINKED VERSUS REGULAR POLYETHYLENE: A PROSPECTIVE RANDOMIZED STUDY WITH TWO YEARS MINIMUM FOLOW-UP USING THE MARTELL METHOD

Abstract

Purpose of the study: The purpose of this propsective randomized study was to evaluate wear resistance of cemented polyethylene cups with the same design but regular or crosslinked polyethylene.

Material and methods: This series included 144 first-intention arthroplasties implanted between July 2000 and July 2002 in 137 patients (92 females, 45 males), mean age 66.2 years (range 16–88 years). The same femoral piece ws used in all patients with a 22.2 mm head. The cup was made of highly crosslinked polyethylene (Durasul™, Zimmer) for 83 hips and regular polyethylene (Duration™, Stryker) for 61 hips). The main outcome criterion was penetration of the femoral head into the cup at two years minimum follow-up (associating true wear and creep) measured with the Martell method modified by the cup manufacturer’s recommendations. Influence of patient-related factors and surgery-related factors was assessed. Non-parametric statistical tests were applied.

Results: The two groups of patients were not significantly different preoperatively. Two patients in the Durasul™ group died at 14 and 31 months follow-up. Median follow-up for the 137 survivors (142 hips) was 28.8 months (range 3–48.8 months) in the Durasul™ group and 24.8 months (ragne 0–47.9) in the Duration™ group. Among these 142 hips, 66 in the Durasul™ group and 51 in the Duration ™ group were reviewed clinically and radiographically with at least two years follow-up. The median penetration was 0.104 mm/yr in the Durasul™ group and 0.242 mm/yr in the Duration™ group (Mann-Whitney test, p=0.01, power 78%). There was a highly significant negative correlation between follow-up time and wear in the Duration™ group (Spearman r = −0.4, p=0.005) but no significant correlation in the Dursul™ group (Spearman r = −0.2, p=0.06).

Discussion and conclusion: The results of this series indicate a notable reduction in wear for highly cross-linked polyethylene cups, with no specific material-related complication. Mid-term results would however be necessary to validate these findings.