This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': '"Head at risk" sign is seen in ? \nSelect and explain. \nA. Pehes disease, B. Ewing\'s sarcoma, C. Osteomylitis, D. Paget\'s disease', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is\'a\'i.e., Pehes disease (Ref: Pediatric Ohopedic Deformities p.326) "Head at risk sign is a radiological prognostic sign for Pehes disease (also k/a Legg-Calves- Pehes disease or Coxa Planaor Idiopathic avascular necrosis of femoral head).', 'role': 'assistant'}]