Regional migratory osteoporosis

a form of transient regional osteoporosis manifested by rapidly developing, self-limiting, and reversible osteoporosis affecting periarticular bone without clear evidence of any precipitating event, such as trauma or immobilization. The knee, ankle, foot and hip are affected most commonly. Local pain and swelling, particularly in the lower extremity, develop rapidly but then diminish and disappear, to be followed by similar involvement in other regions of the same or opposite extremity. Usually the joint nearest to the diseased one is the next to be involved. In some patients only a portion of a joint may be affected. The joint space is maintained, and no intra-articular erosion is seen, although bone scans show increased activity in involved areas. This disorder may be closely related to reflex sympathetic dystrophy and transient osteoporosis of the hip.

MR imaging abnormalities frequently occur in patients with regional migratory osteoporosis, related to bone marrow oedema in the femoral head and neck. Decreased signal intensity on T1-weighted sequences and increased signal intensity in the corresponding region on T2-weighted sequences are typical. Joint effusions in the affected hip are also common. Both the MR imaging findings and the clinical manifestations regress partially or completely over a period of months.