RANDOMISED CONTROLLED TRIAL COMPARING THE PENETRATION RATES OF ZIRCONIA AND STAINLESS STEEL FEMORAL HEADS ON POLYETHYLENE IN TOTAL HIP ARTHROPLASTY

Abstract

Introduction and Aims: Zirconia heads were introduced into hip replacement surgery with in vitro reports of lower wear on polyethylene compared with metal. Over 400,000 zirconia heads have been implanted worldwide and yet clinical studies have varied in their results. The aim of this study was to compare the radiological wear rate of zirconia and stainless steel heads on polyethylene.

Method: Between March 1998 and August 2001, 186 patients having a hip replacement by one of the two authors were entered into a randomised trial to receive either a 26mm stainless steel head, a 28mm stainless steel head or a 28mm zirconia head. In all patients a posterior approach and a cemented Exeter femoral stem were used. One surgeon used a cementless cup in patients under 65. All other patients received an all-polyethylene cemented cup. An upper age limit of 75 was chosen to hopefully allow at least 10 years follow-up. The penetration of the heads into the polyethylene was then assessed by the modified Livermore technique.

Results: Sixty-seven hips were randomised to receive a 26mm metal head, 58 a 28mm metal head and 61 a 28mm ‘HIPed’ zirconia head. The average radiological follow-up was 48 months. The penetration rate on the all-polyethylene cup for the 26mm metal head was 0.06mm/yr. This was equivalent to a previous study using the same components. This compared with a penetration rate of the 28mm metal head of 0.07mm/yr and the 28mm zirconia head of 0.13mm/yr. There was considerable variation in the latter, which is consistent with the theory that some zirconia heads may undergo phase transformation that in turn increases the surface roughness.

Conclusion: Although we have only a short follow-up, this study already shows a statistically significant difference in the penetration rates produced by zirconia femoral heads on polyethylene when compared with stainless steel heads. This agrees with several other clinical studies, but to our knowledge is the first reported randomised trial.