[Selectively upward placement of acetabular implants in patients with anatomically abnormal acetabulum during total...

To investigate the method and effectiveness of selectively upward placement of acetabular implants in patients with anatomically abnormal acetabulum during total hip arthroplasty (THA).

Twenty-six cases (26 hips) of anatomically abnormal acetabulum received THA between January 2005 and December 2010, including 22 cases of developmental dysplasia of the hip, 3 cases of osteonecrosis of the femoral head, and 1 case of post-traumatic arthritis. There were 5 males and 21 females with an average age of 52.3 years (range, 35-67 years). The left hip was involved in 11 cases and the right hip in 15 cases. The preoperative Harris score was 45.85 +/- 10.04. The anteroposterior X-ray films and CT scan of the pelvis, anteroposterior and lateral X-ray films of the femur, and TraumaCad analysis were performed routinely before operation. The principles of acetabular implants were that more than 70% of the bone-implant interface was covered, and the upward distance of acetabular implant was less than 15 mm.

Acetabular implants were placed within 5 mm from the anatomical rotation center in 11 cases. The upward distance of acetabular implant was 5-10 mm in 8 cases and was 10-15 mm in 7 cases. No bone fracture or nerve injury was observed intraoperatively. All incisions healed by first intention, and no infection or lower limb deep venous thrombosis occurred. One case had dislocation at 3 days after operation, and was cured after reduction and conservative treatment. The follow-up time ranged from 15 to 71 months (mean, 34 months). The Harris score was 91.42 +/- 3.59, showing significant difference when compared with preoperative score (t = 20.099, P = 0.000). The Harris scores were 92.09 +/- 4.04 in patients having less than 5 mm upward distance, 91.25 +/- 2.82 in patients having 5-10 mm upward distance, and 90.57 +/- 3.95 in patients having 10-15 mm upward distance, showing no significant difference (F = 0.377, P = 0.690). No loosening or subsidence of the implant was observed by X-ray film during the follow-up.

The acetabular implants should be placed as close to anatomical rotation center as possible according to the principle. However, appropriate upward distance of the acetabular implants (< or = 15 mm) could be acceptable to meet 70% coverage of bone-implant interface and the implant stability. A satisfactory mid-term effectiveness can be obtained, but long-term effectiveness should be further investigated.