[Transient osteoporosis of the hip in magnetic resonance imaging]

This study was aimed at assessing the MR patterns of transient osteoporosis of the hip and, consequently, the role of MRI in the diagnosis and follow-up of this condition. Even though this condition was originally observed in pregnant women, young or middle-aged men are most frequently affected. There is a spontaneous onset of pain, usually progressing over several weeks. The patients have no risk factors for osteonecrosis; they may have a history of minor trauma and there is a possible relationship to the third trimester of pregnancy. Laboratory values are negative. Pain may be severe enough to cause the patient to limp and to impair joint function. The possible causes of transient osteoporosis have been debated by many authors and include trauma, synovitis, neurovascular dysfunction and transient or reversible ischemia. Transient osteoporosis is a self-limiting disease which does not require surgical treatment. The differential diagnosis of transient osteoporosis of the hip is very important because this condition may simulate cancer, septic arthritis, osteomyelitis or avascular necrosis. We report the initial and follow-up features of transient osteoporosis of the hip on the MR images of 6 patients (M/F = 5/1; age: 37-49 years, mean: 41.8 years). The right side was involved in 3 patients, the left side in 2 patients. The patient with bilateral transient osteoporosis was a woman in the 3rd trimester of pregnancy. In all patients, MRI was performed with an 0.5 T MR unit. The MR changes in our 6 patients were rather uniform and included heterogeneous decrease in the signal intensity of the affected bone marrow on T1-weighted images and increased signal intensity on T2-weighted and STIR images, with no evidence of focal lesions. This pattern is known as the "bone marrow edema" (BME) pattern. All the patients received conservative treatment. The clinical symptoms and the MR abnormalities regressed completely within 6-10 months, with no late sequelae. To conclude, this follow-up MR study demonstrates the transient, reversible character of transient osteoporosis of the hip. Until the natural history of the BME pattern is better understood, we suggest a conservative management of this condition, especially in the patients with no risk factors for osteonecrosis. Radiographic and MR follow-up is recommended.