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
The position of arm in posterior dislocation of shoulder is: 
Select and explain. 
A. By the side, B. In internal rotation, C. In adduction, D. In external rotation
B: In internal rotation
Answer: B: In internal rotation 
Explanation: Position of arm in posterior dislocation of shoulder It is difficult to diagnose because the patient may have normal contour of shoulder. Patient holds the injured shoulder in internal rotation and examiner cannot externally rotate it. Ref: Rockwood and Green's Fractures in Adult 6/e, Page 1285-1300.