Subscapularis muscle: the rotator cuff muscle on the front of the scapula

What it is

The largest rotator cuff muscle, filling the subscapular fossa.

Location

Originates from the subscapular fossa of the scapula and inserts onto the lesser tubercle of the humerus.

Function

Medially rotates the arm and stabilizes the humeral head in the glenoid cavity.

Body system

Muscular · paired (left and right)

FMA ID

FMA13414 (Foundational Model of Anatomy)

Key facts

• Innervation: upper and lower subscapular nerves (C5–C6)
• Blood supply: subscapular artery
• It is the only rotator cuff muscle on the anterior (costal) surface of the scapula; its tendon blends with the front of the shoulder joint capsule.

Subscapularis is a strong triangular muscle that fills the subscapular fossa, the shallow hollow on the costal surface of the scapula that faces the back of the rib cage. Its fibres run laterally and narrow into a rounded tendon that crosses the front of the shoulder joint. (Kenhub: Subscapularis.)

Because the scapula sits against the back of the chest wall, subscapularis lies between the scapula and the ribs. It forms most of the posterior wall of the axilla (armpit), and serratus anterior covers its upper lateral part. (Kenhub: Subscapularis.)

It is the only rotator cuff muscle on the costal surface of the scapula. Supraspinatus, infraspinatus and teres minor all arise from the back (dorsal surface) of the scapula and insert on the greater tubercle. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

Origin: the medial two-thirds of the muscle arise from the subscapular fossa and from several tendinous septa (sheets of tendon) inside the muscle. The remaining fibres arise from an aponeurosis covering the posterior surface of the lateral third of the muscle. (Kenhub: Subscapularis.)

Insertion: the tendon inserts on the lesser tubercle (lesser tuberosity) of the humerus and the anterior part of the shoulder joint capsule. The posterior surface of the tendon blends with the fibrous capsule of the glenohumeral joint, so the muscle reinforces the front of the joint. (Kenhub: Subscapularis.)

Subscapularis medially rotates the arm and adducts it, and it helps to hold the humeral head in the glenoid cavity of the scapula. (University of Washington Musculoskeletal Atlas: Subscapularis.)

It is the only medial (internal) rotator among the four rotator cuff muscles, and it adducts the arm to a lesser extent. Kenhub describes it as an important stabiliser of the shoulder joint. (Kenhub: Subscapularis.)

Subscapularis is the largest and strongest cuff muscle. In the transverse (horizontal) plane it forms a force couple with infraspinatus and teres minor: subscapularis pulls the humeral head from the front while the two posterior muscles pull from behind. When this couple is balanced, the head stays centred in the glenoid. (Pandey V, Willems WJ. Rotator cuff tear: a detailed update. 2015.)

Subscapularis is supplied by two nerves, the upper and lower subscapular nerves. Kenhub gives their roots as C5 and C6; the University of Washington atlas gives C5, C6 and C7. The atlas lists the subscapular artery as its arterial supply. (University of Washington Musculoskeletal Atlas: Subscapularis.)

Both nerves are minor branches of the posterior cord of the brachial plexus. TeachMeAnatomy calls them the superior and inferior subscapular nerves, which are the same nerves as the upper and lower subscapular nerves. The thoracodorsal nerve is another branch of the same cord. (TeachMeAnatomy: The Brachial Plexus.)

The lower subscapular nerve also supplies teres major, which arises from the inferior angle of the scapula and, like subscapularis, medially rotates the arm. (Kenhub: Teres major muscle.)

Kenhub describes the arterial supply as several branches of the subclavian artery system: the axillary artery, its subscapular branch, and the suprascapular artery from the thyrocervical trunk. (Kenhub: Subscapularis.)

The anterior surface of subscapularis faces the contents of the axilla. Its central part is crossed by the cords of the brachial plexus and their branches, including the axillary nerve, and by the axillary artery and vein. (Kenhub: Subscapularis.)

A large subscapular bursa (a fluid-filled sac) separates the subscapularis tendon from the neck of the scapula and communicates with the shoulder joint cavity. (Kenhub: Subscapularis.)

Clinical tests for subscapularis ask the patient to rotate the arm inward against resistance at different angles of shoulder flexion. In the lift-off test the patient puts the back of the hand on the lower back and tries to lift it away from the spine; inability to do so is positive. In the belly-press test the patient presses the palm into the abdomen; the test is positive if the elbow drops backwards. (Cotter EJ et al. Comprehensive Examination of the Athlete's Shoulder. Sports Health. 2018.)

A 2021 meta-analysis pooled four tests: bear-hug, belly-press, internal rotation lag sign and lift-off. All had specificity above 0.90, so a positive test makes a tear likely, but all had sensitivity below 0.60; the bear-hug test was the most sensitive (0.55). The authors concluded that no single clinical test is reliable enough to diagnose a subscapularis tear on its own. (Lädermann A et al. Diagnostic Accuracy of Clinical Tests for Subscapularis Tears: A Systematic Review and Meta-analysis. 2021.)

The belly-press test can be done when pain or stiffness stops the patient from putting the hand behind the back, an advantage over the lift-off test. (Lädermann A et al. Diagnostic Accuracy of Clinical Tests for Subscapularis Tears: A Systematic Review and Meta-analysis. 2021.)

The rotator cuff muscles share one job, pulling the humeral head into the glenoid, but differ in movement. Subscapularis medially rotates the arm; infraspinatus and teres minor laterally rotate it; supraspinatus abducts it. Subscapularis is also the only cuff muscle supplied by the subscapular nerves rather than the suprascapular or axillary nerves. (TeachMeAnatomy: The Intrinsic Muscles of the Shoulder.)

All four cuff muscles with a comparison table and 3D view. Rotator cuff muscles.

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

• Scapula · skeletal
• Infraspinatus muscle · muscular
• Teres major · muscular
• Teres minor · muscular
• Dorsal scapular artery · cardiovascular
• Thoracodorsal artery · cardiovascular
• Spinal part of deltoid · muscular
• Circumflex scapular artery · cardiovascular
• Subscapular artery · cardiovascular
• Serratus anterior · muscular