A comparison of polyethylene wear in hips with cobalt-chrome or zirconia heads - A prospective. Randomised study

We have reviewed 70 patients with bilateral simultaneous total hip arthropl asties to determine the rate of failure and to compare polyethylene wear an d osteolysis between an implant with a cobalt-chrome head and Hylamer liner with that of a zirconia head and Hylamer liner. The mean thickness of the polyethylene liner was 11.0 mm (8.8 to 12.2) in the hip with a zirconia hea d and 10.7 mm (8.8 to 12.2) in that with a cobalt-chrome head. At follow-up at 6.4 years no acetabular or femoral component had been revis ed for aseptic loosening and no acetabular or femoral component was loose a ccording to radiological criteria in both the cemented and cementless group s. The mean rate of linear wear and annual wear rate were highest in the 22 mm zirconia femoral head (1.25 mm (sn 1.05) and 0.21 mm (SD 0.18), respect ively) and lowest in the 22 mm cobalt-chrome femoral head (0.70 mm (SD 0.39 ) and 0.12 mm (SD 0.07), respectively). The mean volumetric wear was highes t in the 28 mm zirconia femoral head (730.79 mm(3)) and lowest in the 22 mm cobalt-chrome femoral head (264.67 mm(3)), but if the results were compare d by size of the femoral head and type of material there was no statistical difference (p > 0.05), Sequential measurements of annual wear showed that the zirconia femoral head had a relatively higher rate of penetration than the cobalt-chrome head over the first three years; thereafter the rate of w ear was reduced and compared favourably with that of cobalt-chrome heads. There was a statistically significant relationship between the wear of the polyethylene liner and the age of the patient, male gender and the degree o f abduction angle of the cup, but not diagnosis, weight, hip score, range o f movement, or amount of anteversion. Osteolysis was identified on both sid es of the acetabulum in six patients (9%). Of 12 hips with acetabular osteo lysis, six had a 28 mm cobalt-chrome femoral head and the remaining six a 2 8 mm zirconia head. Osteolysis was observed in zones 1A and 7A of the femur in two hips (3%) with a 28 mm zirconia head (cemented hip) and in four (6% ) with a 28 mm cobalt-chrome femoral head (cementless hip). Our findings suggest that although the performance of a zirconia femoral he ad with a Hylamer liner was not statistically different from that of a coba lt-chrome femoral head and Hylamer liner, there was a trend for the zirconi a head to be worse than the cobalt-chrome femoral head.