Subscapularis Muscle Anatomy

The subscapularis muscle is a thick, triangular muscle that lies on the costal surface of the scapula and forms part of the posterior wall of the axilla. It crosses the anterior aspect of the scapulohumeral joint on its way to the humerus. The subscapularis is the primary medial rotator of the arm and also adducts it. It joins the other rotator cuff muscles in holding the head of the humerus in the glenoid cavity during all movements of the glenohumeral joint (i.e., it helps stabilize this joint during movements of the elbow, wrist, and hand).

The subscapularis muscle is one of the four rotator cuff muscles alongside with supraspinatus, infraspinatus, teres minor the SITS muscles).

Subscapularis Muscle Anatomy

Origin & Insertion

The subscapularis muscle occupies the subscapular fossa, representing the only anterior muscle of the rotator cuff complex. This large, triangular muscle originates from the subscapular fossa of the scapula, covering approximately its entire surface. The muscle fibers converge laterally to form a robust tendon that inserts into the lesser tubercle of the humerus and the anterior aspect of the proximal humeral shaft.

See Also: Rotator Cuff of the Shoulder

Innervation & Blood Supply

The subscapularis muscle receives its primary innervation from the upper and lower subscapular nerves, branches of the posterior cord of the brachial plexus (C5-C6). The arterial supply primarily derives from the subscapular artery, a major branch of the axillary artery, with additional contributions from the circumflex scapular artery. This rich vascular network ensures adequate blood supply during sustained muscular activity.

Functional Significance

The subscapularis muscle serves as a primary internal rotator of the glenohumeral joint. Beyond this primary action, it functions as a critical dynamic stabilizer of the anterior shoulder joint. During arm elevation, the subscapularis works synergistically with other rotator cuff muscles to maintain optimal humeral head positioning within the glenoid fossa, preventing excessive anterior translation.

Clinical Implications

The subscapularis muscle’s anatomical position and functional importance make it susceptible to various pathological conditions. Tears of the subscapularis tendon, while less common than supraspinatus tears, can significantly impact shoulder function. Clinicians should note that isolated subscapularis tears often present with subtle clinical signs, requiring careful examination and appropriate imaging studies for accurate diagnosis.

References & More

1. Journal of Shoulder and Elbow Surgery https://www.jshoulderelbow.org/
2. Clinical Anatomy https://onlinelibrary.wiley.com/journal/10982353
3. Journal of Anatomy https://onlinelibrary.wiley.com/journal/14697580