[MRI-controlled outcome after core decompression of the femur head in aseptic osteonecrosis and transient bone marrow edema].

Purpose: We evaluated the signal changes of avascular necrosis and transient bone marrow oedema before and after core decompression of the femoral head to deduce prognostic factors for this operative procedure.

Method: 38 to 40 cases with core decompression (35 patients, medium age 44 years) were analysed with a mean follow-up time of 26 months. Preoperatively patients were staged by the ARCO classification. MR-images were judged in accordance to the criteria of Mitchell and Steinberg. The clinical outcome was analysed according to the hip index of Merle D'Aubigne.

Results: All hips with transient bone marrow oedema showed normal signal patterns at an average of 3 months after core decompression. In stage I and II, all patients with a preoperative necrosis area less than 30% of the femoral head showed a reduction of the necrotic zone and good clinical results. An unchanged or progressive appearance was observed in necrotic lesions with more than 30% head involvement. Because of failure a renewed operation had to be done in all patients with stage III and IV.

Conclusion: In the case of transient bone marrow oedema, a restitutio ad integrum can be achieved with core decompression. In stage I and II of avascular necrosis, the successful outcome depends on the lesion size of the femoral head. Necrotic lesions less than 30% seem to have the best prognosis. In stage III and IV, core decompression cannot be recommended.