Medial translation of the hip joint center associated with the Bernese periacetabular osteotomy.

This study assessed medial translation of the hip joint achieved by the Bernese periacetabular osteotomy (PAO) in correcting residual acetabular dysplasia deformities. 86 hips in 75 patients with an average age of 25 years (range, 12-50) were treated for symptomatic acetabular dysplasia with a periacetabular osteotomy. Radiographic analysis was performed to assess correction of the acetabular deformity with specific attention to the horizontal position of the hip joint center. All hips were followed until bony union of the iliac osteotomy and the average follow-up was 28 months. The lateral center edge angle improved an average 31.6 degrees (-0.4 degrees preoperative, 31.2 degrees at follow-up). The anterior center edge angle improved 39.3 degrees (-4.5 degrees to 34.8 degrees). The acetabular roof obliquity improved an average 21.8 degrees (25.1 degrees to 3.3 degrees). Preoperatively, the average distance from the medial aspect of the femoral head to the ilioischial line was 17.6 mm. This distance was decreased to an average 7.8 mm postoperatively. This change resulted in an average medial translation of the hip joint center of 9.8 mm, (range -6 to 31mm). Overall, some degree of medial translation of the hip joint center was obtained in 79 (92%) of the hips. Four (5%) were maintained in the same horizontal position, and 3 (3%) had slight lateral repositioning. For the hips translated medially, the average change was 10.0 mm, and 72% of all hips had an optimal correction with the distance between the medial aspect of the femoral head and the ilioischial line being between 0 and 10 mm. This study demonstrates that in addition to optimizing femoral head coverage, a major and distinct advantage of the periacetabular osteotomy is reproducible and consistent medial translation of the hip joint center.