The rotator cuff is a group of muscles and their tendons in the shoulder which connect the humerus scapula. The muscles in the rotator cuff include teres minor, infraspinatus, supraspinatus and subscapularis
Along with the teres major and the deltoid, the four muscles of the rotator cuff make up the six scapulohumeral muscles of the human body. Scapulohumeral muscles are those muscles that connect to the humerus and scapula.
[Read about Rotator Cuff Injury, Rotator cuff tendonitis, and shoulder impingement syndrome]
Structure of Rotator Cuff
Supraspinatus muscle
Supraspinatus muscle takes origin from supraspinous fossa of scapula and inserts into a superior and middle facet of the greater tuberosity. The main function of supraspinatus is to abduct the arm particularly at the beginning of the abduction.
Supraspinatus muscle is supplied by the suprascapular nerve.
Infraspinatus muscle
Infraspinatus muscle originates from infraspinous fossa of the scapula and inserts into a posterior facet of the greater tuberosity. Infraspinatus rotates the arm externally. It is also supplied by the suprascapular nerve.
Teres minor muscle
Teres minor takes origin from the middle half of lateral border of scapula and inserts into an inferior facet of the greater tuberosity. It externally rotates the arm and is supplied by the axillary nerve.
Subscapularis muscle
Subscapularis muscle originates from subscapular fossa of the scapula and inserts into either lesser tuberosity or humeral neck.
It functions to rotate the arm internally.
The subscapularis is supplied by upper and lower subscapular nerve.
The tendons of these four muscles converge to form the rotator cuff tendon which along with the articular capsule, the coracohumeral ligament, and the glenohumeral ligament complex, blend into a confluent sheet before insertion into the humeral tuberosities.
The infraspinatus and teres minor fuse near their musculotendinous junctions, while the supraspinatus and subscapularis tendons join as a sheath that surrounds the biceps tendon at the entrance of the bicipital groove. The insertion site of the rotator cuff tendon at the greater tuberosity is often called as the footprint.
Blood Supply of Rotator Cuff
Blood supply to the rotator cuff is derived from 6 arteries
- Anterior humeral circumflex is a major supplier to anterior cuff & long head of the biceps
- Posterior humeral circumflex supplies the posterior cuff along with its suprascapular branch
- Thoracoacromial arteries supply the supraspinatus
- Suprascapular artery
- Suprahumeral artery
- Subscapular artery
Significance of Rotator Cuff
Apart from being rotator of the shoulder, rotator cuff also acts as a dynamic stabilizer of the shoulder joint, and hold the head of the humerus in the small and shallow glenoid fossa of the scapula. For example, during elevation of the arm, the rotator cuff compresses the glenohumeral joint in order to allow the large deltoid muscle to further elevate the arm and thus increase the efficiency of the deltoid muscle.
As noted before, the greater tuberosity has three facets into which insert the tendons of the supraspinatus, the infraspinatus, and the teres minor. The tendon of the subscapularis muscle inserts on the lesser tuberosity. The bicipital groove separates the two tuberosities. The tendon of the long head of the bicep lies in this groove.
Rotator cuff tendonitis, shoulder impingement syndrome, and rotator cuff injuries are common, particularly in sportspersons. Being in proximity, biceps afflictions, and rotator cuff problems may affect each other.
The rotator cuff muscles and tendons play important roles in the pattern of fracture displacement of the upper humerus.
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