This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Rheumatoid Arthritis, Subject name: Orthopaedics
[{'content': 'Which joint is spared in Rheumatoid arthritis \nSelect and explain. \nA. MP joints of hand., B. DIP joints of finger, C. PIP joints of finger, D. Atlanto-axial joint', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e. DIP joints of finger. DIP joint is characteristically spared in RA.Joint most commonly involved in RA Metacarpophalangeal joints especially of index finger.", 'role': 'assistant'}]