FIVE YEAR OUTCOME OF CHARNLEY TOTAL HIP ARTHROPLASTY WITH A ZINCONIA-POLYETHYLENE BEARING

Abstract

Purpose of the study: Long-term outcome of Charn-ley total hip arthroplasty (THA) (more than 30 years follow-up) has demonstrated that the longevity of these prostheses is inversely proportional to polyethylene wear and head penetration into the cup. In order to limit wear phenomena, we have used since 1997 a Charnley THA with a 22.225 mm zirconia (Zr) head (Prozyr®, Saint-Gobain Desmarquet). The goal was to reduce wear and improve implant longevity.

Material and methods: We reviewed at minimum five years follow-up 62 patients with 69 THA with a standard Zr/PE bearing. These patients had undergone surgery in 1997–1999, the cup or the high-density PE insert were furnished by Centerpulse Zimmer. The measurement method correlated the Livermore technique with determination of the center of the head using the Chevrot and Kerboull method and interobserver radiological measurements made on digitalized images after magnification.

Results: At mean six years follow-up, the Postel-Merle-d’Aubigné score was 17.6 and overall anteroposterior wear at mast follow-up was 0.76 mm (0.73 mm with the Acoplot PE cup and 0.78 mm with the hybrid THA with an isofit cup). Mean wear for this series of implants was thus 0.12 mm/year. There were no fractures of the Zr heads. The rate of osteolysis was 10% with very minimal osteolysis defects, general in the Merckel spine. Wear on the same implant in a previous series operated on in 1997 was 0.40 mm at three years, i.e. also 0.12 mm/year.

Discussion: Wear was not greater with the Zr/PE bearing than usually observed with a 22.225 metal-backed PE bearing. This is in contradiction with observations by J. Allain and D. Goutallier in 1999 and with the publication by P. Piriou (SOFCOT 2003). Furthermore, we did not observe, like Hamadouche (SOFCOT 2001) major osteolytic lesions. On the other hand, we did not observe, as was shown by Wroblewsk, any decrease in the rate of penetration of the head into the PE insert. Using the same 22.225 Prozyr bearing with conventional PE and a cemented head, Wbroblewski showed in 2004 that at mean 4.3 years follow-up (range 0–8 years) mean penetration was 0.03 mm/yr.

Conclusion: Today, at five years follow-up, we have found that with a Charnley THA wear is the same with the Zr/PE as with the metal/PE bearing.