Pre- and postoperative three-dimensional computed tomography analysis of triple innominate osteotomy for hip dysplasia.

Traditional methods of analysis and surgical techniques for hip dysplasia concentrate on frontal-plane analysis of the hip. More recent studies on imaging and operative correction of hip dysplasia recommend three-dimensional (3D) analysis, and some have mentioned but not emphasized the importance of transverse-plane acetabular anatomy (anteversion/retroversion). In this study we found that failure to analyze and understand transverse-plane acetabular anatomy can contribute to complications after triple innominate osteotomy (TIO). A subset of seven patients (eight hips) who were treated with TIO for deficient acetabular coverage resulting from hip dysplasia or Legg-Calvé-Perthes disease had both pre- and postoperative 3D computed tomography (CT) studies. Most of the postoperative studies were obtained to analyze complications (external limb rotation, nonunion). Analysis of the 3D CT studies showed a change in the position of the acetabular fragment after osteotomy into greater adduction, anterior rotation (extension), and external rotation, improving femoral head coverage. All of the hips had increased external rotation of the acetabulum after TIO. Excessive external rotation (>10 degrees) was noted in five hips, and these included two hips with pubic osteotomy nonunion, two with ischial nonunion, and one with marked external rotation of the lower limb. External rotation of the acetabular fragment during redirectional pelvic osteotomy can result in (a) excessive external rotation of the lower limb, (b) decreased posterior coverage, (c) increased gaps at the pubic and/or ischial osteotomy sites with resultant higher rates of nonunion, and (d) lateralization of the joint center. The surgical technique for TIO should be designed to avoid excessive external rotation of the acetabular fragment.