Rotator cuff muscles: the four muscles that hold the shoulder together

The tendons of subscapularis, supraspinatus, infraspinatus and teres minor connect the scapula to the humerus and form the rotator cuff, also called the musculotendinous cuff: a ring of tendons around the shoulder joint. Students often remember the four with the mnemonic SITS (supraspinatus, infraspinatus, teres minor, subscapularis). (OpenStax Anatomy and Physiology 2e, 11.5: Muscles of the Pectoral Girdle and Upper Limbs.)

All four arise from the scapula. Supraspinatus fills the supraspinous fossa above the spine of the scapula, infraspinatus fills the infraspinous fossa below it, teres minor arises along the lateral border, and subscapularis fills the subscapular fossa on the front (costal) surface that faces the ribs. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

Three cuff tendons insert on the greater tubercle of the humerus, one above the other: supraspinatus on the superior facet, infraspinatus on the middle facet and teres minor on the inferior facet. Subscapularis is the odd one out. It inserts on the lesser tubercle, on the front of the humerus. (University of Washington Musculoskeletal Atlas: Supraspinatus.)

The shoulder joint trades stability for movement: the glenoid cavity is shallow and the humeral head is large. Even at rest, the tone of the cuff muscles pulls the humeral head into the glenoid fossa, which makes the joint more stable. On top of this shared job, each cuff muscle has its own movement. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

A detailed review describes the main function of the cuff as keeping the humeral head depressed and centred in the glenoid fossa, so that the arm turns around a single centre of rotation. This is often called concavity compression. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2015.)

The cuff works through two balanced pairs of forces, called force couples. In the coronal (front-facing) plane the upward pull of the deltoid is balanced by the lower cuff muscles, infraspinatus, subscapularis and teres minor. In the transverse (horizontal) plane subscapularis at the front is balanced by infraspinatus and teres minor at the back. The same review notes that subscapularis is the largest and strongest cuff muscle. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2015.)

Individually, supraspinatus abducts the arm (lifts it out to the side), infraspinatus and teres minor rotate it laterally (outward), and subscapularis rotates it medially (inward). (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

Supraspinatus arises from the supraspinous fossa and inserts on the superior facet of the greater tubercle. It is supplied by the suprascapular nerve and the suprascapular artery. The University of Washington atlas gives the nerve roots as C4, C5 and C6; most texts give C5 and C6. (University of Washington Musculoskeletal Atlas: Supraspinatus.)

TeachMeAnatomy teaches that supraspinatus performs the first 0 to 15 degrees of abduction and then assists the deltoid from 15 to 90 degrees. Its tendon passes under the coraco-acromial arch, and it is the cuff tendon most often affected by rotator cuff tendonitis, because it rubs against the arch during abduction. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

The suprascapular nerve comes from the superior (upper) trunk of the brachial plexus. It passes through the suprascapular notch beneath the superior transverse scapular ligament, supplies supraspinatus, then curves through the spinoglenoid notch to reach infraspinatus. (Kenhub: Suprascapular nerve.)

Full page on the supraspinatus: course, actions, impingement and tears. Supraspinatus muscle.

Infraspinatus arises from the infraspinous fossa and inserts on the middle facet of the greater tubercle. It laterally rotates the arm and helps to hold the humeral head in the glenoid cavity. Like supraspinatus it is supplied by the suprascapular nerve (C5 and C6); its blood comes from the suprascapular and circumflex scapular arteries. (University of Washington Musculoskeletal Atlas: Infraspinatus.)

Origin, insertion, action, nerve supply and clinical tests. Infraspinatus muscle.

Teres minor arises from the upper two-thirds of the lateral border of the scapula, just below infraspinatus, and inserts on the greater tubercle. It laterally rotates the arm. Its blood supply comes from the circumflex scapular and posterior circumflex humeral arteries. (Kenhub: Teres minor.)

The University of Washington atlas places the teres minor insertion on the inferior facet of the greater tubercle and lists its nerve as the axillary nerve (C5 and C6). This makes teres minor the only cuff muscle not supplied by the suprascapular or subscapular nerves. (University of Washington Musculoskeletal Atlas: Teres minor.)

The axillary nerve is a continuation of the posterior cord of the brachial plexus. It leaves the axilla through the quadrangular space, winds around the surgical neck of the humerus, and supplies both teres minor and the deltoid. (TeachMeAnatomy: The Axillary Nerve.)

Subscapularis arises from the subscapular fossa and inserts on the lesser tubercle of the humerus. It medially rotates and adducts the arm and helps to hold the humeral head in the glenoid cavity. It is supplied by the upper and lower subscapular nerves (the atlas gives C5, C6 and C7) and by the subscapular artery. (University of Washington Musculoskeletal Atlas: Subscapularis.)

The superior (upper) and inferior (lower) subscapular nerves are both minor branches of the posterior cord of the brachial plexus. (TeachMeAnatomy: The Brachial Plexus.)

The largest cuff muscle: relations, nerves and the lift-off and belly-press tests. Subscapularis muscle.

Teres major is not part of the rotator cuff, because it does not attach to the capsule of the glenohumeral joint. It arises from the posterior surface of the inferior angle of the scapula and inserts on the medial lip of the intertubercular sulcus (bicipital groove) of the humerus. Its lower margin runs parallel to the upper border of latissimus dorsi. (Kenhub: Teres major muscle.)

The two teres muscles act in opposite directions. Teres major adducts and medially rotates the arm and is supplied by the lower subscapular nerve (C6 and C7 in the atlas). Teres minor laterally rotates the arm and is supplied by the axillary nerve. (University of Washington Musculoskeletal Atlas: Teres major.)

Between the two teres muscles lies the quadrangular space. Its borders are the lower margin of teres minor above, the upper margin of teres major below, the long head of triceps brachii medially and the surgical neck of the humerus laterally. The axillary nerve and posterior circumflex humeral artery pass through it, and compression here causes quadrangular space syndrome. (TeachMeAnatomy: Quadrangular Space.)

The intrinsic shoulder muscles run from the scapula or clavicle to the humerus. Besides the four cuff muscles, this group includes the deltoid and teres major. The deltoid arises from the lateral third of the clavicle, the acromion and the spine of the scapula and inserts on the deltoid tuberosity of the humerus; its middle fibres are the main abductor of the arm. It is supplied by the axillary nerve. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

OpenStax groups the muscles of the shoulder by what they move: some position the pectoral girdle (for example trapezius, rhomboids and serratus anterior), while others move the humerus. Two muscles that move the humerus, pectoralis major and latissimus dorsi, are axial muscles; the rest, including the cuff muscles, deltoid and teres major, arise from the scapula. (OpenStax Anatomy and Physiology 2e, 11.5: Muscles of the Pectoral Girdle and Upper Limbs.)

Rotator cuff tears are very common and are often silent. In an ultrasound screening of 664 residents of one Japanese village, 22.1% had a full-thickness cuff tear. No tears were found in people in their 20s to 40s, but prevalence rose to 36.6% in people in their 80s. About two-thirds of the tears (65.3%) caused no symptoms. (Minagawa H et al. Prevalence of symptomatic and asymptomatic rotator cuff tears in the general population. J Orthop. 2013.)

Most degenerative tears begin in supraspinatus. Pandey and Willems report that more than 90% start and spread from the junction between the anterior and middle-posterior fibres of the supraspinatus tendon. They also note that a zone 10 to 15 mm from the supraspinatus insertion has traditionally been regarded as an area of poor blood supply. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2015.)

Rotator cuff tendonitis means inflammation of the cuff tendons, usually from repetitive shoulder use. Conservative treatment includes rest, pain relief and physiotherapy; steroid injections and surgery are options in more severe cases. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

The cuff works as a team, so losing part of one tendon does not always stop the shoulder working. Pandey and Willems note that even with a supraspinatus tear, concavity compression from the remaining cuff can still provide a fixed fulcrum for the humeral head to rotate around. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2015.)

The rotator cable, a band of fibres within the cuff, also matters. Small degenerative supraspinatus tears are well tolerated as long as the rotator cable is preserved, and an intact cable lets supraspinatus keep working and helps avoid muscle wasting and fatty infiltration. The review suggests that an intact cable, by keeping the force couples balanced, may explain why some people with tears have well-compensated shoulders. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2015.)

Clinicians test each cuff muscle with its own manoeuvre. In the Jobe (empty can) test the arm is held at 90 degrees of abduction in the plane of the scapula while the examiner pushes down, which stresses supraspinatus. A painful arc between 60 and 120 degrees of abduction often points to cuff pathology. (Cotter EJ et al. Comprehensive Examination of the Athlete's Shoulder. Sports Health. 2018.)

Infraspinatus is assessed with resisted external rotation and the external rotation lag sign, in which the patient cannot hold the arm in external rotation after the examiner lets go. Teres minor is assessed with the hornblower's sign, and subscapularis with the lift-off and belly-press tests. No single test is perfect, so clinicians combine several with imaging. (Cotter EJ et al. Comprehensive Examination of the Athlete's Shoulder. Sports Health. 2018.)

Infraspinatus muscle

A rotator cuff muscle on the back of the scapula.

Subscapularis

The largest rotator cuff muscle, filling the subscapular fossa.

Supraspinatus

A rotator cuff muscle on the back of the scapula above its spine.

Teres major

A thick muscle of the posterior shoulder, sometimes called the lat's little helper.

Teres minor

A rotator cuff muscle on the lateral scapula.