- Idiopathic avascular necrosis of the femoral head.
- Bilateral in 10-20% of patients and usually affects children aged 4-8 years.
- When both hips are involved, they are usually affected successively, not simultaneously.
- Rarely occurs in blacks
- In adults, the corresponding condition is termed Chandler disease.
 Imaging Findings
 Plain films
- Early signs
- Small femoral epiphysis (96%)
- Sclerosis of the femoral head with sequestration and collapse (82%)
- Late signs
- Radiolucent crescent line representing a subchondral fracture
- Femoral head fragmentation and femoral neck cysts from intramedullary hemorrhage or extension of physeal cartilage into metaphysis, loose bodies, and coxa plana.
- Coxa magna or remodeling of the femoral head, which becomes wider and flatter and similar in appearance to a mushroom.