This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Joint disorders, Subject name: Orthopaedics
[{'content': 'A 25-year-old man complaints of low backache, decreased lumbar movements, morning stiffness which clinical examination will fuher help: \nSelect and explain. \nA. Head circumference, B. Chest expansion, C. Hyperextension of joints, D. Plantar arch', 'role': 'user'}, {'content': "Answer: B \nExplanation: ANKYLOSING SPONDYLITIS (AS)/MARIE-STRUMPELL OR BECHTEREW'S DISEASE Diagnostic Criteria-Modified New York Criterion CLINICAL CRITERIA Low back pain >= 3 months, improved by exercise and not relieved by rest Limitation of lumbar spine in sagittal and frontal planes Limitation of chest expansion (relative to normal values corrected for age and sex) RADIOLOGICAL CRITERIA Bilateral grade 2-4 sacroiliitis, or; Unilateral 3-4 sacroiliitis", 'role': 'assistant'}]