[Spontaneous fracture of the sacrum due to "insufficiency". An overlooked cause of low lumbago in elderly women].

A case of insufficiency fracture of the sacrum is reported. These fractures usually occur in elderly women and are secondary to various conditions, mainly postmenopausal or steroid-induced osteoporosis and radiation therapy. They are often overlooked or confused clinically and radiographically with metastatic disease. Findings on plain films are often subtle. Radionuclide bone scan shows a characteristic H or butterfly shaped pattern of increased uptake in the sacral alae. The diagnosis is confirmed by conventional tomograms or CT which show the fracture always surrounded by prominent sclerosis.