Rare childhood hip disease called perthes, extreme pain, what is this?

Legg-Calve-Perthes: Legg-calve-perthes disease is a childhood condition that affects the hip ball-and-socket joint when blood supply is temporarily interrupted to the ball part of the joint. That part of the bone then breaks more easily and heals poorly. Children who have had legg-calve-perthes disease are more likely to develop early osteoarthritis in the affected hip joint as adults which is why pain develops.