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': 'All are X-ray findings of RA except: \nSelect and explain. \nA. Reduced joint space, B. Soft tissue shadow, C. Periaicular new bone formation, D. Subchondral cyst', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Radiological features of RA are Evidence of soft tissue swelling and joint effusion Symmetrical involvement Juxta-aicular osteopenia (within weeks) Loss of aicular cailage and bone erosions (after months) Narrowing of joint space Aicular destruction and joint deformity, e.g. subluxation of atlantoaxial and cervical joints Lack of hyperophic bone changes (sclerosis or osteophyte)', 'role': 'assistant'}]