Postoperative dislocation after Charnley low-friction arthroplasty.

The dislocation rate after the Charnley arthroplasty with the 22 mm diameter femoral head was 0.8% in 3,820 arthroplasties performed before 1971. Over this era the annual rate ranged from 0.5% to 1.4% without any apparent explanation. Following the routine use of a low position for the socket in the acetabulum and the Long Posterior Wall design of socket, the dislocation rate fell to 0.4% over 4,706 arthroplasties and the annual dislocation rate over 4 years ranged between 0.5% and 0.2%.