POLYETHYLENE-ZIRCONE TOTAL HIP ARTHROPLASTY: RESULTS AFTER AT LEAST TWO YEARS

Abstract

Purpose: New surfaces have been developed to reduce polyethylene wear. The zircone ceramic surface appears to have a theoretical advantage due to its interesting tribologic properties. The purpose of this prospective study was to assess clinical and radiological outcome at a minimal two years follow-up in a consecutive series of total hip arthroplasties using the polyethylene zircone junction.

Material and methods: La series included 56 total hip arthroplasties performed in 49 patients (30 women and 19 men), mean age 52.2 ± 12 years (25–76). Primary degenerative hip disease was the aetiology in 43% of the cases, dysplasia in 27%. The femoral component was made of 316L steel with a 11°25 Morse cone for 27 hips and a 5°40 cone for 29 hips. The femoral head measured 22.2 mm and was made of polycrystaline zircone ceramic stabilised in the tragonal form with yttrium (Y-TZP). All the arthroplasties were performed via transtrochanteric access using cemented Charnley-Kerboull implants. Clinical outcome was assessed with the Merle-d’Aubigné score. Classical landmarks on the AP pelvis views were used to assess implant migration. Cup wear was measured using the Livermore method. Actuarial survival curves were plotted.

Results: Mean follow-up was 32 months (24–48). None of the patients were lost to follow-up. The mean functional score at last follow-up was 17.8±0.2 (16–18) versus 12.2±2.6 before arthroplasty (Student t test for paired variables, p < 0.0001). No cases of migration of the femoral or acetabular component were observed. Acetabular wear was always less than the precision of the measurement method. Osteolytic lesions were however observed as endosteal defects in the Merkel region measuring less than 1 cm2, observed in 18 out of the 56 hips (32%). These osteolytic lesions generally appeared between the first and second year and did not appear to progress.

Discussion: Osteolysis in the Merkel region appeared early for one third of the hips, despite the absence of cup polyethylene wear. It would be reasonable to be prudent when using zirone ceramic heads. We are continuing our close follow-up of this group of patients. In addition, measurements of wear and migration are being made using the EBRA method.