Crescent sign

In radiology, the crescent sign is a finding on conventional radiographs that is associated with avascular necrosis.

[1][2][3] It usually occurs later in the disease, in stage III of the four-stage Ficat classification system.

[1] It appears as a curved subchondral radiolucent line that is often found on the proximal femoral or humeral head.

[1][4] The crescent sign is caused by the necrotic and repair processes that occur during avascular necrosis.

[1] When the trabeculae experience stress leading to microfractures and collapse, the crescent sign appears.

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.