This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Arthritis, Subject name: Orthopaedics
[{'content': 'Which joint is rarely affected by ankylosing spondylitis - \nSelect and explain. \nA. Ankle, B. Hip, C. Shoulder, D. Sacroiliac', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Ankle Joints involved in ankylosing spondylitis* Ankylosing spondylitis primarily affects axial skeleton.* The disease usually begins in the sacro-iliac joints and usually extends upwards to involve the lumbar, thoracic, and often cervical spine.* In the worst cases the hips or shoulders are also affected. Hip joint is the most commonly affected peripheral joint.* Rarely knee and ankle are also involved", 'role': 'assistant'}]