Supraspinatus muscle: anatomy and action of the top rotator cuff muscle

What it is

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

Location

Originates from the supraspinous fossa of the scapula and inserts onto the superior facet of the greater tubercle of the humerus.

Function

Initiates abduction of the arm and stabilizes the humeral head in the glenoid cavity.

Body system

Muscular · paired (left and right)

FMA ID

FMA32544 (Foundational Model of Anatomy)

Key facts

• Innervation: suprascapular nerve (C5–C6)
• Blood supply: suprascapular artery
• Its tendon passes under the coraco-acromial arch, where it can be pinched between the humeral head and acromion (impingement, painful arc between about 60 and 120 degrees).

Clinical relevance

It is the rotator cuff muscle most often torn.

Origin: supraspinatus arises from the medial part of the supraspinous fossa, the hollow on the back of the scapula above its spine. Its fibres converge on a tendon that runs laterally under the acromion and passes over the top of the glenohumeral (shoulder) joint. (Kenhub: Supraspinatus muscle.)

Insertion: the tendon inserts on the superior facet of the greater tubercle (greater tuberosity) of the humerus. Infraspinatus and teres minor insert on the facets below it. (University of Washington Musculoskeletal Atlas: Supraspinatus.)

Relations: supraspinatus lies deep to the trapezius and above the spine of the scapula and infraspinatus. The subacromial bursa separates its tendon from the coraco-acromial ligament, the acromion and the deltoid, letting the tendon glide during movement. (Kenhub: Supraspinatus muscle.)

Kenhub describes the subacromial (subdeltoid) bursa as lying deep to the deltoid, between the acromion and the supraspinatus tendon. (Kenhub: Deltoid muscle.)

The University of Washington atlas summarises the action as initiating abduction of the arm, assisting the deltoid in abduction, and acting with the other rotator cuff muscles to stabilise the shoulder. (University of Washington Musculoskeletal Atlas: Supraspinatus.)

The classic teaching is that supraspinatus performs the first 0 to 15 degrees of abduction and then assists the deltoid from 15 to 90 degrees. The deltoid, mainly its middle (acromial) fibres, is the major abductor of the arm. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

Kenhub likewise describes the acromial part of the deltoid as abducting the arm once it is beyond the first 15 degrees. The two muscles therefore share abduction rather than working in strict sequence. (Kenhub: Deltoid muscle.)

Supraspinatus is not uniform. Its anterior part has a much larger physiological cross-sectional area than its posterior part (about 140 versus 62 mm² in one study), and the anterior belly is regarded as mainly responsible for abduction and for depressing (holding down) the humeral head, so that the deltoid can lift the arm without the head riding upward. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. 2015.)

Supraspinatus is innervated by the suprascapular nerve, carrying fibres from the anterior rami of C5 and C6. The suprascapular artery, a branch of the thyrocervical trunk, supplies it, and the dorsal scapular artery sometimes adds a collateral supply. (Kenhub: Supraspinatus muscle.)

The University of Washington atlas gives the suprascapular nerve roots as C4, C5 and C6, so some texts include C4. (University of Washington Musculoskeletal Atlas: Supraspinatus.)

The suprascapular nerve arises from the superior trunk of the brachial plexus and runs through the posterior triangle of the neck. It crosses the suprascapular notch beneath the superior transverse scapular ligament, while the suprascapular artery and vein pass above the ligament. It then supplies supraspinatus, passes through the spinoglenoid notch to infraspinatus, and gives sensory branches to the shoulder and acromioclavicular joints. (Kenhub: Suprascapular nerve.)

If the nerve is trapped at the suprascapular notch, both supraspinatus and infraspinatus become weak. If it is trapped lower down, at the spinoglenoid notch, only infraspinatus is affected, because the branches to supraspinatus have already left. Ganglion cysts, trauma, scapular fractures and repetitive overhead activity are recognised causes. (Joo YB, Lee WY, Chung HJ. Suprascapular nerve entrapment caused by a large hematoma of the scapula: a case report. 2023.)

Supraspinatus is the rotator cuff muscle most commonly affected by tendonitis. During abduction its tendon rubs against the coraco-acromial arch, which leads to inflammation and degenerative change in the tendon. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

More than 90% of degenerative rotator cuff tears are reported to start and spread from the junction between the anterior and middle-posterior fibres of the supraspinatus tendon. A zone 10 to 15 mm proximal to its insertion has traditionally been regarded as an area of critical ischaemia (poor blood supply). (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. 2015.)

Full-thickness cuff tears become common with age and are often painless. An ultrasound screening of 664 adults found tears in 22.1% overall, 0% of people in their 20s to 40s, 10.7% in their 50s and 36.6% in their 80s, and 65.3% of tears caused no symptoms. (Minagawa H et al. Prevalence of symptomatic and asymptomatic rotator cuff tears in the general population. 2013.)

A tear does not always mean loss of function. Small degenerative supraspinatus tears are well tolerated as long as the rotator cable, a band of fibres within the cuff, is maintained. An intact cable lets the remaining supraspinatus work optimally and helps it avoid atrophy and fatty infiltration. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. 2015.)

In the Jobe (empty can) test the examiner abducts the arm to 90 degrees in the plane of the scapula and pushes down on the forearm while the patient resists. One study of patients with full-thickness supraspinatus tears found a sensitivity of 52.6% and specificity of 82.4%. (Cotter EJ et al. Comprehensive Examination of the Athlete's Shoulder. Sports Health. 2018.)

Pain between about 60 and 120 degrees of abduction, the painful arc, often indicates rotator cuff pathology. In the drop arm test the arm is passively raised to 90 degrees and the patient is asked to hold it; failure to hold it against gravity suggests a full-thickness tear, although the test misses many tears (35% sensitive). (Cotter EJ et al. Comprehensive Examination of the Athlete's Shoulder. Sports Health. 2018.)

How supraspinatus works with infraspinatus, teres minor and subscapularis. Rotator cuff muscles.

The nearest named structures in the 3D model, measured from the centre of each part:

• Suprascapular artery · cardiovascular
• Circumflex scapular artery · cardiovascular
• Acromial branch of thoraco-acromial artery · cardiovascular
• Axillary artery · cardiovascular
• Deltoid branch of thoraco-acromial artery · cardiovascular
• Subscapular artery · cardiovascular
• Transverse part of trapezius · muscular
• Trunk of thoraco-acromial artery · cardiovascular
• Infraspinatus muscle · muscular
• Posterior circumflex humeral artery · cardiovascular