To assess to what extent does surgical intervention (pelvic osteotomy, femoral osteotomy, shelf acetabular procedure) for children in the active stages of Perthes disease improve outcome as assessed by a Stulberg (Stulberg 1981) or Mose (Mose 1964) classification at skeletal maturity in experimental studies (eg RCT), and controlled observational studies (eg comparative cohort studies and studies using conservative and historical controls).