Surgical advances in periacetabular osteotomy for treatment of hip dysplasia in adults.

Introduction: Hip dysplasia is characterized by an excessively oblique and shallow acetabulum with insufficient coverage of the femoral head. It is a known cause of pain and the development of early osteoarthritis in young adults. The periacetabular osteotomy is the joint-preserving treatment of choice in young adults with symptomatic hip dysplasia. The surgical aim of this extensive procedure is to reorient the acetabulum to improve coverage and eliminate the pathological hip joint mechanics. Intraoperative assessment of the achieved acetabular reorientation is therefore crucial. The "classic" surgical approaches for the periacetabular osteotomy inflict extensive trauma to the tissues and some involve detachment of muscles. The type of surgical approach may affect the occurrence of complications, duration of surgery, intraoperative blood loss, transfusion requirements, and length of hospital stay. The aims of the PhD thesis were I) to assess the outcome of a new, minimally invasive transsartorial approach for periacetabular osteotomy; II) to compare the minimally invasive approach with the previously used "classic" ilioinguinal approach; and III) to assess the reliability of a novel device for intraoperative assessment of the achieved acetabular reorientation.

Methods: Three studies underly this PhD thesis. In studies I and II, the experience with the minimally invasive and ilioinguinal approaches was retrospectively assessed by database inquiry and evaluation of radiographic material. Data regarding patient demographics, patient history, intraoperative measures and complications was recorded in a validated database. Center-edge and acetabular index angles were measured in preoperative and postoperative pelvic radiographs to assess preoperative dysplasia and the achieved acetabular reorientation. The well-defined study groups consisted of 94 and 263 periacetabular osteotomies in studies I and II, respectively. In study III, intraoperative angle measurements were carried out prospectively in 35 periacetabular osteotomies. The obtained measures (center-edge and acetabular index angles) were compared with those of postoperative pelvic radiographs. Furthermore, a cadaver study was conducted to evaluate intra- and interobserver variability of the device and to assess whether pelvic positioning influenced the variability of measurements. The applied methodology was critically reviewed.

Results: Study I--The minimally invasive approach had the following outcome. The mean duration of surgery was 73 min and the median intraoperative blood loss was 250 ml. Blood transfusion was required following 3% of the procedures. There were no cases of moderate or severe technical and neurovascular complications, and the achieved center-edge and acetabular index angles suggest that optimal reorientation can be achieved. Hip joint survival with total hip arthroplasty as the end point was 98% at 4.3 years. Study II--When compared with the outcome of the ilioinguinal approach, the procedures performed by using the minimally invasive approach had a statistically significant shorter duration of surgery, less intraoperative blood loss and hemoglobin reduction, and fewer transfusion requirements. The achieved reorientation was comparable between groups. There were no cases of moderate or severe complications in the minimally invasive group and three cases (3%) of arterial thrombosis in the ilioinguinal group. At follow-up 4.9 years after hip joint surgery, survival rates were 97% in the minimally invasive group and 93% in the ilioinguinal group. Study III--Intraoperatively obtained angle measures differed less than +/- 5 degrees from measurements on postoperative pelvic radiographs, and the intra- and interobserver variability of the device was confined well within +/-5 degrees. Positioning did not influence the variation of angle measurements beyond intraobserver variability of the device.

Interpretation: The new minimally invasive transsartorial approach appears to be a safe technique, allowing optimal acetabular reorientation, and seems to minimize tissue trauma. In addition, short-term hip joint survival rate is encouraging. The outcome compares favorably with that of the ilioinguinal approach, and the results support continued use of the minimally invasive approach for periacetabular osteotomy. Optimal reorientation of the acetabulum is crucial in periacetabular osteotomy. The novel measuring device is a potentially helpful tool for intraoperative assessment of center-edge and acetabular index angels. It is simple to use and facilitates repeated reliable angle measurements during acetabular reorientation, making intraoperative radiographs unnecessary. The new, minimally invasive approach and the novel measuring device represent important surgical advances in contemporary periacetabular osteotomy.