The patient is a 38 year old man without significant past medical history who presents to an orthopedic surgeon with right-sided hip and groin pain of several weeks duration. He denies any antecedent trauma, and the onset of the pain was acute in nature. The discomfort has progressed to the point where he now has significant difficulty bearing weight on the affected side. He denies any recent travel, trauma, fevers, weight loss, skin rashes, joint pain, swelling, or stiffness. He has been using Tylenol and Ibuprofen with little relief, and is becoming increasingly frustrated with his condition. Physical examination reveals an antalgic gait, but there are no other obvious abnormalities. A series of radiographic studies were undertaken.
Plain X-rays of the hips reveal diffuse osteopenia (green arrow, film 1) of the right femoral neck and head. There is no joint space narrowing, scalloping, or fracture noted. The left hip appears normal. MRI studies of the hips demonstrate decreased marrow signal on T1 images (yellow arrow, film 2) of the right hip, with striking T2 hyperintensity in the same area (red arrow, film 3). No masses are noted.
Diagnosis and Discussion
Correct Diagnosis: Idiopathic Transient Osteoporosis of the Hip
Idiopathic Transient Osteoporosis of the Hip is a rare and often unrecognized cause of hip pain in otherwise healthy young adults. The condition typically affects middle-aged men and women in the third trimester of pregnancy. Symptoms often present insidiously with pain developing in the affected hip, followed by progressive gait disturbance and functional disability. The diagnosis is suggested once other more common causes of hip pain in young adults are ruled out, such as stress fractures, infections, and malignancy. Laboratory findings are usually normal, although slight elevations in the ESR are sometimes seen. Radiographs may initially be unremarkable, but marked localized demineralization can usually be seen within 1 month of symptoms onset. The diagnosis can be confirmed by T1 and T2-weighted MRI, which usually demonstrates characteristic hypointense T1 and hyperintense T2 signal of the affected region.
Most cases resolve spontaneously within 6-12 months regardless of therapy. Multiple therapeutic modalities have been described, including NSAIDs, calcitonin, intravenous/oral bisphosphonates, steroids, sympathetic blockade, casting, and rest. Recovery is noted radiographically as well, with complete remineralization of the previously osteoporotic area.
The etiology of this rare condition is unknown, but several hypotheses have been proposed. These include mechanical compression of local nerves, fibrinolytic system abnormalities leading to early AVN, unmasking of pre-existing subclinical osteoporosis in young women, and the development of regional neuropathies. However, none of these theories adequately account for the transient nature of the condition.
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