Perthes disease is a rare childhood condition that affects the hip. It occurs when the blood supply to the rounded head of the femur (thighbone) is temporarily disrupted. Without an adequate blood supply, the bone cells die, a process called avascular necrosis. As the condition progresses, the weakened bone of the head of the femur (the “ball” of the “ball-and-socket” joint of the hip) gradually begins to collapse. Over time, the blood supply to the head of the femur returns and the bone begins to grow back.Treatment for Perthes focuses on helping the bone grow back into a more rounded shape that still fits into the socket of the hip joint. This will help the hip joint move normally and prevent hip problems in adulthood.