Avascular necrosis of the femoral head can occur at any age with risk factors including corticosteroid treatment, alcohol excess, obesity, scuba diving and sickle cell disease.

Insufficiency fractures within the subchondral bone disrupt the blood supply, become more progressive and result in eventual collapse of the articular surface.

Early signs on plain radiographs may include reduced bone density and the 'crescent sign' of subchondral lucency, with later radiographs demonstrating more conspicuous collapse of the bony cortex.