<prompt> Head at risk sign is seen in -Perthes diseaseEwings sarcomaOsteomylitisPagets disease  <response>: Ans. is a i.e., Perthes disease o Head at risk sign is a radiological prognostic sign for Perthes disease also ka Legg-Calves- Perthes disease or Coxa Plana or Idiopathic avascular necrosis of femoral head.o Disease mainly affects children o Classification of Head at risk sign :i Lateral subluxation most important prognostic factor: due to articular cartilage overgrowthii Calcification lateral to epiphysis: calcification in the overgrown cartilageiii Osteolysis in the superolateral part of the femoral metaphysis: Gages signiv Horizontal physisv Metaphyseal cysts. 