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': "Most common cause of Bony ankylosis \nSelect and explain. \nA. TB Hip, B. TB Knee, C. Septic arthritis, D. Pott's spine", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]