Abstract
The aim of this study was to measure polyethylene wear in uncemented metal-backed cups and compare it with cemented ultra-high molecular weight (UHMW) polyethylene cups in a controlled double-blind study.
The study group was made up of 91 patients aged 50 to 70 years undergoing THR for unilateral OA of the hip between February 1995 and July 2002. The male to female ratio was 40:60. In all patients, a cemented stem and 28-mm ceramic head was inserted, using a third-generation cementing technique and UHMW polyethylene. Patients were randomly allocated to receive either a cemented or uncemented acetabular cup. Eight patients were lost to follow-up.
Cemented cups were used in 28 patients (mean age 64 years). The mean thickness of the polyethylene was 9.6 mm (7.5 to 12.5). The mean liner thickness in the metal-backed cups was 8.9 mm (7 to 12.2). In measuring wear, baseline 3-month postoperative radiographs were compared with the most recent follow-up radiographs and Martell software was used.
The polyethylene in metal-backed cups had a mean wear rate of 0.49 mm at 4.7 years, with a mean annual wear rate of 0.12 mm. The cemented polyethylene cups had a mean wear rate of 0.45 mm at 5.3 years, with a mean annual wear rate of 0.11 mm.
The study is ongoing. Currently we conclude that there is no significant difference in the annual wear rate of polyethylene in uncemented metal-backed cups and cemented cups.
Secretary: Dr H.J.S. Colyn, Editor: Professor M.B.E. Sweet. Correspondence should be addressed to SAOA, Box 47363, Parklands, Johannesburg, 2121, South Africa.
