Wear Rates of XLPE Nearly 50% Lower Than Previously Thought After Adjusting for Initial Creep: An RCT Comparing 4 Bearing Combinations

BACKGROUND: The ideal bearing combination for total hip arthroplasty (THA) remains debatable. Highly cross-linked polyethylene (XLPE) is widely used, but long-term wear rates are not fully known, nor is how much the initial “creep,” if any, affects overall wear. Additionally, the use of oxidized zirconium (OxZir) is purported to lower polyethylene wear rates, but this has not been proven. We present the 10-year data of a cohort of patients who underwent THA. Patients were prospectively randomized to 1 of 4 bearing combinations: a conventional ultra-high molecular weight polyethylene (UHMWPE) or XLPE acetabular liner coupled with either a cobalt-chromium (CoCr) or OxZir femoral head. The aims of the study were to (1) assess the extent to which creep affected overall wear rates and (2) assess wear rates between OxZir and CoCr with polyethylene. METHODS: A total of 92 hips (92 patients) between the ages of 22 and 65 years (mean, 52.2 ± 9.3 years) were randomized to 4 groups. At 10 years, 70 (76%) of the hips were available for analysis; patients who had undergone revision, had died, or were lost to follow-up were excluded from final analysis. Radiographic analysis was performed using a validated digital assessment program to determine linear, volumetric, and directional wear of the polyethylene for all 4 bearing couples. Radiographic assessments were performed immediately postoperatively, at 6 and 12 weeks, and then annually for a minimum of 10 years. RESULTS: XLPE had significantly lower wear rates than UHMWPE. Once creep was eliminated, annual and overall wear rates were nearly 50% lower than have been previously reported. This was proportionally more important in the XLPE group than in the UHMWPE group. There was a nonsignificant trend toward a lower wear rate with OxZir heads. CONCLUSIONS: Creep plays a notably more important role than first thought. Once creep was eliminated, the overall wear rate was even lower than previously assumed. This has important implications for the overall survivorship of hip arthroplasty implants. LEVEL OF EVIDENCE: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.