This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolic Disorders of Bone, Subject name: Orthopaedics
[{'content': 'A 65-year-old man had H/o of back pain since 3 months. ESR is raised. He also has dorso-lumbar tenderness on examination and mild restriction of chest movements. On X-ray, syndesmophytes are present in veebrae. Diagnosis is: \nSelect and explain. \nA. Ankylosing spondylitis, B. Degenerative osteoahritis of spine, C. Ankylosing hyperostosis, D. Lumbar canal stenosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ankylosing hyperostosis Ankylosing spondylitis Age Elderly Young Sacroilitis Absent Always present Chest expansion Mild restriction Marked but not reliable in elderly Tenderness Dorso-lumbar Sacroiliac ESR Normal to mild rise High Syndesmophytes Present Present', 'role': 'assistant'}]