The rotator cuff
The shoulder joint is a large ball on a small, shallow socket, which lets the arm move further than at any other joint. Four muscles of the scapula hold the ball in the socket. Their tendons blend with the joint capsule and wrap round it like a cuff, the rotator cuff.
Muscles on the back of the scapula, the supraspinatus, infraspinatus and teres minor of the rotator cuff, with the teres major and the triceps brachii, Gray's Anatomy, 1918, figure 412Wikimedia Commons, Henry Vandyke Carter, Public domain (Gray412.png)
The supraspinatus lies above the spine of the scapula and helps raise the arm. The infraspinatus and the teres minor below the spine turn the arm outward. The subscapularis lies on the front of the scapula, against the ribs, and turns the arm inward.
Muscles that move the humerus, from the pectoralis major, the latissimus dorsi and the deltoid to the deep muscles of the shoulder blade, OpenStax Anatomy and PhysiologyWikimedia Commons, OpenStax, CC BY 4.0 (1119 Muscles that Move the Humerus.jpg)
The supraspinatus tendon passes through a narrow gap between the head of the humerus and the acromion. There it can be pinched when the arm is raised, and with age it wears. Tears of the rotator cuff become common after middle age, and most involve this tendon.
Sources
- Susan Standring (ed.), Gray's Anatomy, 42nd ed. (2020), chapter on the shoulder girdle and arm.
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