Anatomic basis of Tonnis' triple pelvic osteotomy for acetabular dysplasia

Dysplasia of the hip in adults can be treated by a pelvic osteotomy. In order to assess pelvic anatomy in relation to surgical approach and osteotomy sites, 12 cadaver hips were studied. A triple pelvic osteotomy as described by Tonnis [6] through ilium, pubis and ischium was performed, followed by an intrapelvic and anterior and posterior dissection of the hip. At the ischium, the pudendal and inferior gluteal neurovascular bundles are most at risk medially and proximally respectively. Much less in danger is the sciatic n. as it runs 1 to 3 cm lateral to the osteotomy site. At the pubis osteotomy the femoral v. lies close on the bone and is prone to damage. The artery lies further off the bone. The ilium osteotomy starts just proximal to the anterior inferior iliac spine and exits posteriorly at the sciatic notch. Here the sciatic n. and the superior gluteal neurovascular bundle may be damaged. The practical surgical implications of these three osteotomies are discussed, especially with respect to the requirement of meticulous subperiostal dissection and accurate placement of retractors.