Polyethylene wear of the cup in total hip replacement with Muller reinforcement ring

Abstract

Introduction: Polyethylene (PE) wear contributes to the process of aseptic loosening and is seen asthe one important reason for late failureafter total hip replacement(THR). THR with Muller reinforcement ring (ARR) have showed favourable mid-term survival results, but we found no studies investigating PE wear in combination with ARR. Objectives: The aim of the study was to investigate PE wear in THR with ARR followed ≥10 years. Methods and materials: We performed 321 consecutive primary arthroplasties with ARR in 291 patients, between 1984 and 2002. For long-term wear and radiological analysis THR patients with ARR and cemented PE cup with at least 10 years radiological follow-up were included, leaving 133 THR implanted in 123 patients. For wear analysis linear and volumetric wear were measured. The analysis of age, gender, body mass index, head material, and head size in relation to volumetric wear was conducted using multiple regression analysis. Radiological assessment included evaluation of osteolysis, migration, and loosening. Results: For wear and radiological analysis we included 43 males and 80 females with a mean age of 65 years (31-86, SD 10) and a mean follow-up of 13 years (10-23, SD 3.6). Out of 133 ARR, 9 were classified as loose and out of those 4 had osteolysis. Mean PE linear wear rate for all hips was 0.06 mm/year (SD 0.51), volumetric - 37 mm3/year (SD 25.5). The loose ARR had a mean wear rate of 0.07 mm/year (SD 0.04), volumetric - 52 mm3/year (SD 32.3). The highest wear rates were found for hips requiring acetabular component revision (mean 0.09 mm/year, SD 0.04, mean 64 mm3/year, SD 38.1). Only larger head size diameter independently of head material affected increased volumetric wear in multiple regression analysis, p<0.001. Conclusions: We conclude that THA hips with ARR followed >10 years showed favourable wear rates as compared to conventional cups, larger head diameter being the only factor affecting greater volumetric wear.