Final answer:
In the AP projection of the shoulder in internal rotation, the anatomy best demonstrated includes the lesser tubercle and anterior structures of the shoulder joint.
Step-by-step explanation:
The AP projection of the shoulder in internal rotation best demonstrates the lesser tubercle of the humerus and the shoulder joint's anterior structures. In internal rotation, the greater tubercle is moved posteriorly, allowing for better visualization of the lesser tubercle on a radiograph.
The shoulder joint, or glenohumeral joint, facilitates a wide range of movement, combining motions such as flexion/extension, abduction/adduction, and medial/lateral rotation. The intricacy of the joint is due to its ball-and-socket structure, with the head of the humerus moving within the glenoid cavity of the scapula. The glenoid labrum, a fibrocartilaginous rim, deepens the glenoid cavity, enhancing joint stability.
Given the shoulder's complex anatomy, the internal rotation view is crucial for assessing the articulation of the humerus with the glenoid cavity, visualizing anterior structures, and examining the boney landmarks, including the lesser tubercle, in the context of shoulder injuries or other medical conditions.