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: Orthopaedics
[{'content': "A woman of 45, a known cause of pemphigus vulgaris on a regular treatment with controlled primary disease presented with pain in the right hip and knee. Examination revealed no limb length discrepancy but the patient has tenderness in the scarpa's triangle and limitation of abduction and internal rotation of the right hip joints as compared to the other side. The most probable diagnosis is - \nSelect and explain. \nA. Stress fracture of neck of femur, B. Avascular necrosis of femoral head, C. Perthe's disease, D. Transient synovitis of hip", 'role': 'user'}, {'content': 'Answer: B \nExplanation: This patient has\n\n\nPemphigus vulgaris taking treatment (steroid is the DOC).\nPain in hip and knee (Pain of hip can refer to hip).\nLimitation of abduction & internal rotation.\n\n\nDiagnosis is AVN of hip.', 'role': 'assistant'}]