The subscapularis is innervated by the upper and lower subscapular nerves (C5-C8). Its origin is at the subscapularis fossa, and the upper two-thirds inserts onto the lesser tuberosity, whereas the inferior third inserts onto the humeral metaphysis.

The subscapularis is the strongest of the rotator cuff muscles. It acts to internally rotate the humerus along with the teres major, latissimus dorsi, and pectoralis major muscles. It resists anterior and inferior translation of the humeral head.¹³,²³

The upper fibers of the subscapularis and the anterior fibers of the supraspinatus contribute to the rotator interval as well as the transverse humeral ligament.

The coracohumeral ligament is the roof of the rotator interval and blends with the supraspinatus and subscapularis. The coracohumeral ligament and the superior glenohumeral ligament are the primary stabilizers of the biceps.³

The biceps muscle is innervated by the musculocutaneous nerve (C5-C6). It is composed of a long head, which originates from the supraglenoid tubercle, and a short head, which originates from the coracoid process. Both heads insert onto the bicipital tuberosity of the radius and the ulnar fascia of the forearm.

The long head of the biceps tendon provides superior shoulder stability when the arm is abducted. It also provides posterior shoulder stability when the arm is in midranges of elevation.²⁰,²⁷

The coracoid is located just anterior to the superior border of the subscapularis. It projects laterally, anteriorly, and inferiorly toward the glenoid.

In the young patient, subscapularis tears occur as a result of trauma. The typical mechanisms include hyperextension of an externally rotated arm or forced external rotation of an adducted arm.⁶,¹⁰,¹¹

In older patients, a tear is typically degenerative in nature, although it may be the result of a glenohumeral dislocation or other trauma.¹⁹,²¹,²²

Frequently, there is associated long head of the biceps pathology. This may include tenosynovitis, subluxation, dislocation, degeneration, or complete rupture.¹⁶,²⁵

Subcoracoid impingement may also be a cause of subscapularis tendon tears. Subcoracoid distance of less than 6 mm is defined as stenosis and significantly increases the risk of tears.¹⁷ The normal coracohumeral interval is between 8.4 and 11 mm.⁹,¹²

Isolated subscapularis tendon ruptures are relatively rare. Subscapularis tears are often associated with tears of the supraspinatus and infraspinatus.

One study found that subscapularis tears occur in 8% of rotator cuff tears.⁸

A magnetic resonance imaging (MRI) study was performed on 2167 patients with rotator cuff tears.¹⁶

One study found a high correlation between subscapularis tendon tears and medial biceps subluxation, biceps tendinopathy, superior labral pathology, and fluid within the subscapular recess or the subcoracoid space.¹⁶,²⁵

A recent MRI review study of 47 full-thickness subscapularis tears analyzed patient age, tear size, muscle volume loss, Goutallier grade, biceps pathology, coracohumeral distance, and associated rotator cuff tears.¹⁵

Patients with complete tears of the subscapularis have increased passive external rotation compared with the unaffected shoulder.

Several muscles contribute to internal rotation of the shoulder, including the pectoralis major, latissimus dorsi, and teres major, and can compensate for loss of the subscapularis.

The lift-off test isolates the subscapularis muscle.¹⁰ Inability to lift the hand off the back is a positive test. It is the most specific test for subscapularis tears.²⁹

Internal rotation lag sign¹⁴: The examiner measures the lag between maximal internal rotation and the amount the patient can maintain.

Belly press (Napoleon test)²⁹: A positive test is the inability to bring the elbow forward. An intermediate test is the ability to bring the elbow forward partially. A positive test indicates a complete rupture, whereas an intermediate test indicates a partial tear of the subscapularis.

The bear hug test¹: If the examiner is able to lift the patient’s hand off the opposite shoulder, then the patient likely has a partial or complete tear of the upper subscapularis tendon.

Coracoid impingement⁷: Reproduction of pain or a painful click indicates a positive test. A positive test indicates impingement of the coracoid onto the subscapularis.

Speed test⁵: If the maneuver produces pain or tenderness, the test is positive, which may indicate bicipital pathology, although the test is not specific.