Influence of the volume of osteonecrosis on the outcome of core decompression of the femoral head

Objectives—To assess the outcome of core decompression in the treatment of osteonecrosis of the femoral head related to the volume of necrotic bone measured according to a previously reported method. Methods—Twenty hips corresponding to strictly Ficat stage II underwent magnetic resonance imaging and the volume of necrotic bone was expressed as a percentage of the volume of the entire head measured on each slice. All hips underwent core decompression and the outcome was evaluated at 24 months. The primary evaluation criterion was radiological appearance: the outcome was considered as good if the hip remained stage II and poor if the disease progressed. Results—Twenty four months after core decompression, half the cases remained stable and in half the disease had progressed. Outcome seemed to be related to the volume of necrotic bone (average 22% in the good outcome group versus 45% in the poor outcome group (p = 0.0051)) and was independent of risk factors, age, and histological type. Conclusions—The volume of necrotic bone should be taken into account in the evaluation of any treatment, bearing in mind that in more than one third of cases this volume will probably decrease, especially at the beginning of the disease process. (Ann Rheum Dis 1997;56:747‐750) The treatment of osteonecrosis of the femoral head (ON) remains controversial, both in the early stages of the disease when the femoral head is still spherical and in later stages when the head isflattened. 1 In thefirst instance, core decompression is the classic treatment. A recent general review of the medical literature 2 concluded that core decompression of the femoral head and neck gave an overall 64% clinical success rate and 63% showed no disease progression on radiographs, compared with 23% and 27% respectively for conservative treatment. Total hip arthroplasty was later necessary in 80% of cases treated conservatively compared with 23% of those treated by core decompression. Magnetic resonance imaging (MRI) makes it possible to diagnose ON in early stages when plain radiographs are still normal or