The aim of this essay is to study different causes of failed open reduction of developmental dysplasia of the hip (redislocation, acetabular dysplasia, and avascular necrosis of proximal femur) and lines of treatment.This well be achieved through the discussion of causes of failed open reduction of DDH which are attributed to technical errors, treatment of failed open reduction of DDH by revision operation, pelvic osteotomy and femoral osteotomy, and discussion of avascular necrosis of the proximal femur through studying of blood supply of the proximal femur, risk factors, prevention, classification, diagnosis, the prognostic importance of ossific nucleus, and surgical management.