This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Involvement of the joints of hand is relatively uncommon in which of the following ahritis? 
Select and explain. 
A. Ankylosing spondylitis, B. Reactive ahritis, C. Psoriatic ahritis, D. Rheumatoid ahritis
A: Ankylosing spondylitis
Answer: A: Ankylosing spondylitis 
Explanation: Ans. is 'a' i.e., Ankylosing spondylitis 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 shouldersare also affected. Hip joint is the most commonly affected peripheral joint. Rarely knee and ankle are also involved.