Randomized controlled trial comparing 9 different hip resurfacing designs with a follow-up of 5 years

Damien Van Quickenborne, Catherine Van Der Straeten, Koen De Smet


Background: A randomized controlled trial (RCT) comparing nine different hip resurfacing designs was set up at an independent hip resurfacing center to assess the possible differences between the designs. There was one operating surgeon. All surgeries were performed between 2007 and 2011.
Methods: The RCT was set-up to include 180 patients scheduled for a unilateral hip resurfacing arthroplasty (HRA) who had no other metal implants and normal renal function, randomized to receive 1 of 9 different HRA designs (20 per group). Surgical data (instrumentation), clinical and radiographic outcome and metal ion levels in whole blood and serum chromium (Cr) and cobalt (Co) at preoperative, 3, 6, 12, 24 and 60 months intervals were compared.
Results: During the course of the study three designs were discontinued: the ASR after withdrawal from the market and the DUROM and MITCH because of cup fixation problems. Patients already recruited and operated were kept in the study for follow-up. The other groups were ACCIS, ADEPT, BHR, Conserve Plus, Conserve Plus Aclass, and RECAP. A total of 129 patients were included in the RCT. There was no significant difference in gender between the HRA groups (P=0.435). There were more men (61.1%) included than women (38.9%). There were 9 revisions (7%) at a mean of 31.3 months (range, 11–60 months). Harris Hip Scores had a range of 86–100 (mean 98) with a median of 100 over 5 years. There was a high correlation between the whole blood and serum levels for Cr and Co (P<0.001). In all groups except ACCIS, Cr and Co ion concentrations increased from baseline (preoperative) till the 1-year follow-up (running-in phase) and subsequently levelled off (steady-state). Outliers occurred more often in the RECAP and ASR groups.
Conclusions: Clinical and radiographical follow-up showed little differences. Overall the revision ratio, at a minimum of 8 years of follow-up was 7%. Thus, in our series, the implants of 9 different hip resurfacing designs, including the ones that were withdrawn from the market, have globally performed well with <1% failure per year. In general, metal ion levels below the proposed acceptable limits were found with all HRA designs. The difference in ion levels between the resurfacing designs may reflect differences in clearance, metallurgy and coverage angle. Outliers occurred more often with designs with a smaller coverage angle. The lower ion levels with the DUROM design are probably related to its highest coverage angle and its metallurgy.