Treatment of grade III osteonecrosis of the femoral head with a Charnley/Bicentric hemiarthroplasty.

Thirty-eight hips with Charnley/Bicentric hemiarthroplasties were reviewed. Preoperatively all hips had a Grade III osteonecrosis (Arlet & Ficat) of the femoral head. Follow-up ranged from 42 to 72 months with a mean of 56 months. The mean age was 36 years (range 16-52 years). Three hips with gross loosening of the femoral prosthesis were revised to a cementless total hip replacement: a further two hips exhibited radiological changes indicative of loosening and pending failure. In one hip with progressive loss of joint space and secondary degenerative changes the Bicentric cup was revised to a cemented Charnley component. Acetabular migration was not encountered. Six of 38 hips (15.8%) were thus considered failures. The mean total movement from full abduction to full adduction at the cup-acetabular articulation was 21 degrees, compared to 14 degrees at the inner component articulation. The results of cemented femoral components are predictably unfavourable in this young age group. However, the double articulation of the bipolar cup offers an acceptable method of treatment for this grade of osteonecrosis in the medium term.