"Head at risk" sign is seen in -

Ans. is 'a' i.e., Perthes disease o "Head at risk" sign is a radiological prognostic sign for Perthes disease (also k/a 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: Gage's signiv) Horizontal physisv) Metaphyseal cysts.