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: Surgery
[{'content': 'Which of the following is not usually involved in ankylosing spondylitis? \nSelect and explain. \nA. Sacroiliac joint, B. Spine, C. Ankle, D. Elbow', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Usually axial skeleton is severely involved. Elbow joint is not involved. Commonest joint involved is Sacroiliac joint.', 'role': 'assistant'}]