Anatomical changes in the pelvis after modified Chiari pelvic osteotomy.

Abstract

Although plain X-ray analysis is able to reveal anatomical changes in the frontal plane of the pelvis after Chiari pelvic osteotomy involving medial displacement (medialization) in the distal fragment and lateral displacement (lateralization) in the proximal fragment, changes in the horizontal or sagittal plane can not be discerned. Here, I have investigated three dimensional changes in the pelvis using CT in 22 patients before and after Chiari pelvic osteotomy. The various changes were investigated. Medialization in the distal fragment (average 0.4 cm) occurred in the 14 cases and to a slight extent in the other 8 cases. Also anterior or posterior displacement, and anterior rotation occurred in the distal fragment. Lateralization in the proximal fragment (average 0.8 cm) occurred in 19 cases and to a slight extent in the other 3 cases. Furthermore, the acetabular coverage over the femoral head, assessed by superimposing the acetabular region over the femoral head, improved by about 30% of the anterior half of femoral head and by about 20% of the posterior half of femoral head. It is suggested that the acetabular coverage over the femoral head is most affected by lateralization in the proximal fragment.