[Bone marrow edema--an early form of femur head necrosis]

We examined 15 patients (16 hips) with painful hips whose radiographs were either normal (n = 9) or showed a minimal decrease in radiodensity (n = 7). The available bone scintigrams of 9 cases were positive. T1-weighted images visualised a diffuse signal loss of the bone marrow in all hips, with various extensions in the head, neck, and intertrochanteric area. These regions were hyperintensive on T2-weighted images. Focal anomalies were not seen in any of the cases. All patients underwent core decompression treatment. Histology of 13 hips confirmed not only the presence of bone marrow oedema but of bone changes corresponding to those of avascular necrosis. Follow-up examinations with MR after core decompression showed normal signal intensity in all cases. Magnetic resonance represents a viable diagnostic tool for identifying bone marrow oedema. Due to our histological results bone marrow oedema should be included in the differential diagnosis as an early stage of necrosis of the hip.