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
Synovial chondromatosis commonly affects 
Select and explain. 
A. Hands, B. Knees, C. Pelvis, D. Vertebrae
B: Knees
Answer: B: Knees 
Explanation: None