During the Neer Impingement Sign Test, which structure is involved in jamming into the anteroinferior surface of the acromion?

The Neer Impingement Sign Test is designed to evaluate for impingement of the rotator cuff tendons, particularly the supraspinatus, which can be affected by the anatomy of the shoulder, including the greater tuberosity. During this test, when the arm is raised, the greater tuberosity of the humerus can come into contact with the anteroinferior surface of the acromion. This jamming occurs primarily due to the anatomical relationships of the shoulder structures, where the greater tuberosity is situated at the proximal end of the humerus, and, when elevated, it moves into a position where it can become impinged against the acromion.

The other structures mentioned play roles in shoulder mechanics but are not directly involved in this specific impingement scenario during the test. For instance, the coracoid process is more related to the attachment of muscles and ligaments rather than direct articulation that results in impingement. The humeral head is the joint surface, but its role in this context is less about jamming and more about overall shoulder movement. Finally, the subscapularis is a muscle of the rotator cuff located on the anterior aspect of the shoulder, but