Transient Osteoporosis of the Hip / Regional Migratory Osteoporosis

The combination of acute atraumatic hip pain worse on weight-bearing in a middle-aged man, or a woman in the third trimester of pregnancy, with diffuse bone marrow oedema of the femoral head on MRI, is characteristic of transient osteoporosis of the hip, a self-limiting bone marrow oedema syndrome. The crucial step is to distinguish it from avascular necrosis: in transient osteoporosis the MRI oedema is diffuse throughout the femoral head and neck with a small effusion but no focal subchondral lesion, crescent sign or collapse, whereas avascular necrosis is a focal segmental subchondral lesion that can progress to collapse; I would also exclude septic or inflammatory arthritis and an occult or subchondral insufficiency fracture. Radiographs may later show femoral head osteopenia with a preserved joint space and no collapse. Management is conservative because the condition resolves over about six to twelve months: protected, reduced weight-bearing with crutches both relieves pain and protects the weakened head from a subchondral insufficiency fracture, together with analgesia and reassurance. Bisphosphonates or prostacyclin analogues such as iloprost can speed recovery, though bisphosphonates are avoided during pregnancy and breastfeeding, and core decompression is occasionally used in refractory cases. In the pregnant patient I would manage with rest, analgesia and protected weight-bearing in conjunction with obstetrics, deferring bisphosphonates until after delivery and breastfeeding.

I protect weight-bearing because the femoral head in transient osteoporosis is transiently demineralised and oedematous, so its subchondral bone is mechanically weakened; continuing full weight-bearing through it risks a subchondral insufficiency fracture and secondary collapse, which would convert a benign self-limiting condition into a structural problem. Reduced weight-bearing with crutches also relieves the pain while the oedema resolves over the months the condition takes to settle. Regional migratory osteoporosis is a related entity within the same bone marrow oedema syndrome spectrum, in which the oedema and pain do not stay in one joint but migrate over time from one region to another - for example from one hip to the contralateral hip, or to the knee or ankle - with each site going through the same self-limiting cycle. It is recognised by this migratory clinical pattern and the characteristic MRI oedema in the currently affected joint, and it is managed the same conservative way, protecting the affected joint, with analgesia and time, and considering bisphosphonates or iloprost if needed.