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: Orthopaedics
NOT true about psoriatic arthritis 
Select and explain. 
A. CASPER Criteria, B. Involves DIP, C. Pencil in cup deformity, D. Bamboo sign
D: Bamboo sign
Answer: D: Bamboo sign 
Explanation: None