Idiopathic transient osteoporosis: a hidden cause of hip pain.

Idiopathic transient osteoporosis must be considered in active young adult and middle-aged patients who have spontaneous joint pain with acute onset. This often debilitating condition most commonly affects the hip; it is then marked by pain that intensifies with weight bearing or hip rotation. The knee, ankle, or foot can also be affected. Delayed diagnosis is common, in part because of a lack of physician familiarity with the condition. Physical exam tests can reproduce pain, and scintigraphy and MRI can help narrow the differential. Treatment is typically supportive and includes pain relief and physical therapy to maximize function. Two case reports illustrate management of the condition.