Legg-Calvé-Perthes syndrome is a degenerative disease of the hip joint, where a loss of bone mass leads to some degree of collapse of the hip joint, that is, to deformity of the ball of the femur and the surface of the hip socket. The disease is typically found in young children and small dogs, and it can lead to osteoarthritis in adults.

It is the idiopathic avascular osteonecrosis of the capital femoral epiphysis of the femoral head. It is caused by an interruption to the blood supply of the head of the femur close to the hip joint. It is equivalent to adult avascular necrosis.

It is also known as Perthes disease,^[1] ischemic necrosis of the hip, coxa plana, osteochondritis and avascular necrosis of the femoral head, or Legg-Perthes Disease or Legg-Calve-Perthes Disease (LCPD).