A Comparison of the Fixation Stability of the Osteotomy Fragment of the Bernese Periacetabular Osteotomy of Ganz with Tonnis' Modification of Steel's Triple Innominate Osteotomy

Introduction Periacetabular osteotomies are performed for improvement of femoral head coverage in a variety of clinical scenarios. A number of osteotomies are in clinical use today, and they differ in surgical technique, amount of coverage attainable, and biomechanical strength. The use of the triple innominate osteotomy in North America was popularized by Steel. In Tonnis' modification of the osteotomy, the level of the ischial cut is above the level of the sacrospinous attachment to the ischium. Tonnis believes that freeing the acetabular fragment from its attachments to the pelvic floor ligaments allows increased mobility of the osteotomized fragment. The Bernese periacetabular osteotomy has also been well described in the literature and enjoys widespread clinical use. This procedure, first described by Ganz, allows rotation of the acetabular fragment free from its attachment to the pelvic floor ligaments and preserves a portion of the posterior column. It is theorized that this allows minimal intraoperative fixation and early postoperative weightbearing. This osteotomy violates the triradiate cartilage, however, and cannot be performed in skeletally immature individuals, making the triple innominate osteotomy a necessary surgical alternative. We believe that there is little difference in the biomechanical stability between these two osteotomies.