Legg-Calvé-Perthes, or “Perthes”, disease is a childhood injury to the weight-bearing growth center of the ball (femoral head) of the hip joint. It typically affects children (males more than females) from ages 4-8. For unknown reasons, the blood supply to the bone directly below the weight-bearing cartilage is injured. Without a normal blood supply, the bone undergoes progressive necrosis (dies) making it weak. As the bone weakens it can begin to collapse with continued weight-bearing. As the bone collapses, the ball becomes flattened and deformed. Frequently, as a result, the hip socket grows to match the deformed head resulting in hip dysplasia. The combination of the deformed ball and shallow socket leads to a combination of painful hip instability and hip impingement, both of which can lead to cartilage and hip labrum tears and eventual arthritis. Treatment is dependent on a patient’s age. Younger patients (less than 6-8 years) can be treated with observation, activity modification and protective weight-bearing. Older patients often require a surgical dislocation of the hip (SDH) along with a corrective osteotomy of the socket or thigh bone to properly re-align the hip socket.