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.