IMAGING

THE USE OF MR IMAGING SELECTION CRITERIA TO OPTIMIZE RESULTS OF TROCHANTERIC ROTATIONAL OSTEOTOMY IN OSTEONECROSIS OF THE FEMORAL HEAD

Kyung-Hoi Koo, Jin-Won Yang, Yong-Chan Ha, Kang-Il Kim
Department of Orthopaedic Surgery, Gyeong-Sang National University School of Medicine, 90 Chilam-dong, Chinju 660-702, South Korea

PURPOSE: Osteonecrosis of the femoral head occurs in young patients. The preservation of the hip joint is vitally important, because hip replacement arthroplasty is associated with high rates of failure. Transtrochanteric rotational osteotomy is one of several joint preserving procedures, but it has been associated with variable rates of success. The success rate of osteotomy might be improved if patients were selected by magnetic resonance imaging (MRI), because the extent of osteonecrosis can be estimated accurately by using this technique. In the present study, the author formulated selection criteria for the osteotomy of suitable patients using MRI.

METHODS: The three selection criteria used included the following: patients with an early collapsed osteonecrotic hip (loss of congruity or crescent sign) without a narrowing of joint space or acetabular involvement; patients younger than 55 years and with a painful hip; and patients with an intact area represented by an arc of more than 120° (the arc between the central vertical line of the femoral head and the posterior margin of the necrotic portion seen on midsagittal MRI scan). Forty-one patients (43 hips) who met these predefined criteria underwent operation. Patients underwent the osteotomy with 65° to 90° rotation and 15-20° of additional varus positioning. Postoperative bone scans were obtained at 4 weeks after surgery to evaluate the blood perfusion of the proximal segment. Every 3 months, the patients were assessed by clinical examination, using the scoring system of Merle d'Aubigne et al. and plain radiographs. Radiological failure of the operation was defined as a sinking of the surface by 2 mm or more compared with the contour of the immediate postoperative radiograph.

RESULTS: One patient was lost to follow-up and 40 patients (42 hips) had follow-up for a period of 24 to 84 months (mean, 40 months). A postoperative bone scan at 4 weeks showed adequate perfusion of the proximal segment in all of 42 hips. Further collapse of the femoral head occurred in four hips, and three of the four patients required a total hip arthroplasty. In the remaining 36 patients (38 hips) the hip score improved from a mean of 13.1 points, preoperatively, to a mean of 17.2 points at the latest follow-up.

CONCLUSION: The use of MRI criteria instead of plain radiographic criteria for the selection of patients improved the success rate of transtrochanteric rotational osteotomy.