This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Upper Extremity, Subject name: Anatomy
A 22-year-old male soccer player is forced to leave the game following a head-to-head collision with another player. He is admitted to the hospital, and radiographic examination reveals slight dislocation of the atlantoaxial joint. As a result, he experiences decreased range of motion at that joint. What movement of the head would most likely be severely affected? 
Select and explain. 
A. Rotation, B. Flexion, C. Abduction, D. Extension
A: Rotation
Answer: A: Rotation 
Explanation: The atlantoaxial joint is a synovial joint responsible for rotation of the head, not flexion, abduction, extension, or adduction. The atlanto-occipital joint is primarily involved in flexion and extension of the head on the neck.