Computer tomography evaluation of the hip joint after Chiari osteotomy.

Background. The goal of our study was to evaluate hip joints after Chiari osteotomy in computer tomography images, and to specify the field of coverage of the femoral head by the acetabulum. Material and methods. We evaluated treatment outcome in 27 patients who were treated at the Clinic of Orthopedics at the Poznan University of Medical Sciences during the period from 1965 to 1990. A Chiari osteotomy was performed on all patients for hip decentration or hip subluxation after developmental dysplasia. During the follow-up examination we evaluated the hips using CT scans taken at the greatest diameter of the femoral head and at the acetabulum level. Results. A wide area of femoral head coverage was most characteristic in the horizontal plane of the hip; the mean degree of femoral head coverage was 89.92%, which exceeded normal by 20%. On the computer tomograms taken at the greatest diameter of the femoral head the measurements were done with using the sector angles of Anada: anterior (ASA), posterior (PSA), and horizontal (HAS), as well as the anteversion angle (AA). The sector angles of Anada were within the normal range in most of these patients. Conclusions. When conducted correctly, Chiari osteotomy considerably improves femoral head coverage in the transverse plane.