
The rotator cuff is composed of 4 muscles of the shoulder. Each muscle connects from the scapula (shoulder blade) to the greater and lesser tubercle (rounded prominences of bone where muscles attach) of the humerus (upper arm bone), forming a "cuff".
The function of the rotator cuff is to allow for motion of the shoulder joint and to provide stability. The four muscles of the rotator cuff are outlined below, including where each muscle originates and then attaches, the movement each produces, and the nerves that supply (innervate) each muscle:

Supraspinatus Muscle
This muscle originates on the supraspinous fossa (small groove) of the scapula and attaches to the superior (top) and middle facets (small, smooth area of bone) of the greater tubercle of the humerus. Its function is to abduct the arm (raises the arm out to the side). It is innervated by the suprascapular nerve.

Infraspinatus Muscle
This muscle originates on the infraspinous fossa of the scapula and attaches to the posterior (back) facet of the greater tubercle of the humerus. Its function is to externally rotate the arm. It is innervated by the suprascapular nerve.

Teres Minor Muscle
This muscle originates on the middle half of the lateral (outside) border of the scapula and the attaches to the inferior (below) facet of the greater tubercle of the humerus. This muscle also externally rotates the arm. It is innervated by the axillary nerve.

Subscapularis Muscle
This muscle originates on the subscapular fossa of the scapula and attaches to the lesser tubercle of the humerus. Its function is to internally rotate the arm and it is innervated by the upper and lower subscapular nerve.
These four muscles can be remember by the acronym "SITS".
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