COMPARATIVE STUDY OF WEAR IN TWO 22-MM TOTAL HIP ARTHROPLASTY HEADS: ZIRCON/PE AND METAL/PE

Abstract

Purpose: Since 1962, when Sir John Charnley implanted the first total arthroplasty, long-term studies have demonstrated the excellent survival of these implants with greater than 85% survival at 25 years (John Older, Mike Wroblewski, ACORA group in 1995). Polyethylene wear is the main obstacle to long-term survival of the Charnley total hip arthroplasty. New friction surfaces have been proposed to reduce wear, notable the ceramic/ceramic junction proposed by Pierre Boutin since 1970 with the ceramic/polyethylene derivative. The alumine ceramic head cannot be greater than 22.225 cm due to the risk of fracture, leading to the zircone head. D. Goutallier and his school recently demonstrated (1999) that the use of zircone can increase wear with early development of osteolysis and acetabular loosening. For this reason, we compared wear between two series of prostheses using the 22.2 zircone/polyethylene combination versus the metal/polyethylene combination.

Material and methods: Two series of 37 patients were compared for wear. The first series included 41 hips with a zircone/polyethelene combination using a 22.2 cm head. The second series of 38 hips used a metal/polyethylene combination and 22.2 cm heads. The femoral components were the same in the two series with an 8/10 Morse cone. Mean follow-up in the two series was 38 months. All patients underwent surgery in 1997 for the zircone/polyethylene implants and in 1995 for the metal/polyethylene implants. Mean age in the zircone/polyethylene series was 58 years and in the metal/polyethylene series 66. The Postel Merle d’Aubigné (PMA) score at review was 16.6 for the zircone/polyethylene series and 17.7 for the metal/polyethylene series. Manual measurements of wear were made using the Livermore method with determination of the centre of the head according to Cherrot and Kerboull, doubled with computer-assisted interobserver radiological measurements.

Results: At three years, 31.5% of the metal/polyethylene implants were devoid of any signs of wear compared with 29.2% in the zircone/polyethylene implants. Mean wear was 0.19 per year for the metal/polyethylene implants versus 0.12 per year for the zircone/polyethylene implants. Overall wear on the AP view at last follow-up was 0.62 mm for the metal/polyethylene implants and 0.40 mm for the zircone/polyethylene implants at three years. This difference was significant p < à.005).

Discussion: We did not find any greater wear with the zircone/polyethylene combination compared with metal/polyethylene as was also demonstrated by D. Goutallier. M. Wroblewski (2000) demonstrated in a study with 10 years follow-up that wear was twice as great the first two years with a 22.225 diameter head using the alumine ceramic/polyethylene combination (0.1 mm per year), then stabilised. This was probably due to a stabilisation period. We are probably currently in this stabilisation period with the zircone/polyethylene implants.