Use of bipolar hip arthroplasty in states of acetabular deficiency

Bipolar hip arthroplasty was performed on 557 hips from December 1980 to June 1988. The clinical results and serial roentgenograms of 37 hips with acetabular deficiency, treated by arthroplasty from December 1980 to June 1983, were followed for a minimum of five years. The longest follow-up period was seven years and six months after the operation. The clinical score was assessed by the hip rating score of the Japanese Orthopaedic Association, which assigns a maximum of 100 points. The preoperative clinical score ranged from 24 to 56 points (mean, 42.2 points). The postoperative score improved to a range of 71-100 points (mean, 82.7 points). Of 37 hips examined, 31 hips were pain-free. As measured from the serial roentgenograms after the operation, the overall distance of central migration of the prosthesis in 37 hips was 0-5 mm, with an average of 1.4 mm, two years after the operation. At the five-year follow-up evaluation, 27 of 37 hips showed no additional central migration. The overall distance of superior migration of the prosthesis in 37 hips was from 0 to 8 mm, with an average of 2.6 mm, two years after the operation. Additional superior migration was noticed in 18 of 37 hips (48.6%) at the time of this five-year follow-up evaluation.