Osteonecrosis of the hip in renal transplant recipients. Changes in functional status and magnetic resonance imaging findings over three years in three hundred five patients.

OBJECTIVE: to conduct a retrospective study of the appearance and course of magnetic resonance imaging abnormalities in avascular osteonecrosis of the femoral head in renal transplant recipients and of potential relations between these abnormalities and the functional outcome. PATIENTS AND METHODS: among 305 renal transplant recipients, patients with pain in the hips or knees underwent radiographs and magnetic resonance imaging studies of the hips and, if appropriate, of the knees. The mean time interval between these studies and transplantation was 8.9 months. The outcome was evaluated based on the Lequesne index and findings from a repeat magnetic resonance imaging study after a mean follow-up of 33 months since transplantation. The criteria developed by Mitchell et al. were used to diagnose osteonecrosis on magnetic resonance images. The size of the necrotic area was estimated using the tracing paper method as < 25%, 25-50%, > 50% of the surface of the femoral head. Eleven patients were treated by elimination of weight-bearing and conservative treatments and 15 underwent core decompression (radiographic stage I or II). RESULTS: Fourteen patients (4.5%) developed osteonecrosis of the femoral head, which was bilateral in 12 patients and unilateral in two: thus, the total number of hips with osteonecrosis was 26. The first magnetic resonance imaging study disclosed a crescent-shaped area of low signal intensity in 25 cases, most of which were mild in severity as assessed on radiographs (Arlet and Ficat stage I or II). Extensive necrosis was found in most cases at the first evaluation (> 25% in 15 cases and > 50% in eight). The surface of the necrotic area (as assessed irrespective of the treatment used) remained unchanged in 20 cases and decreased in six. In half the cases the hyperintense signal from the sequestrum converted to a hypointense signal after a mean follow-up of 39 years. A poor functional outcome (Lequesne's index > 7 or total hip arthroplasty) was seen in 61.5% of cases, irrespective of the treatment used. CONCLUSION: Avascular osteonecrosis of the femoral head precipitated by corticosteroid therapy in renal transplant recipients occurred in 4.5% of patients immediately involved a large segment of the epiphysis, and usually remained stable over time, although a decrease in the size of the lesion was seen in a few cases. Overall, the functional prognosis was poor, with a Lequesne's index greater than 7 or total hip arthroplasty in two thirds of cases after three years' follow-up. The incidence of avascular osteonecrosis of the hip in renal transplant recipients has decreased since 1980, when cyclosporin was introduced and doses of corticosteroids used to treat rejection episodes were diminished.