A radiograph of a left hip joint, which reveals a thin, curvilinear lucent line parallel to the cortical margin of the femoral head, in a patient with avascular necrosis. In radiology, the<unk>  is a finding on conventional radiographs that is associated with avascular necrosis. It usually occurs later in the disease, in stage III of the four-stage Ficat classification system. It appears as a curved subchondral radiolucent line that is often found on the proximal femoral or humeral head. Usually, this sign indicates a high likelihood of collapse of the affected bone. The<unk>  may be best seen in an abducted (frog-legged) position. The<unk>  is caused by the necrotic and repair processes that occur during avascular necrosis. Osteosclerosis occurs at a margin where new bone is placed over dead trabeculae. When the trabeculae experience stress leading to microfractures and collapse, the<unk>  appears. The<unk>  may be seen with other bone diseases, such as shear fractures.
Crescent sign
Sulcus sign
Amsler sign
Markle sign
Cupola sign
Steeple sign
Westermark sign
White hand sign