Subscapularis muscle

The subscapularis muscle is a large, triangular-shaped muscle located on the anterior surface of the scapula within the subscapular fossa. It is the largest and strongest muscle among the rotator cuff group, which also includes the supraspinatus, infraspinatus, and teres minor muscles.

Origin

The subscapularis muscle originates from the subscapular fossa of the scapula and the lower two-thirds of the lateral (axillary) border of the scapula.

Insertion

The muscle fibers converge laterally to form a tendon that passes in front of the shoulder joint and blends with the capsule before inserting onto the lesser tubercle of the humerus.

A large bursa lies between the tendon and the neck of the scapula, facilitating smooth movement and communicating with the shoulder joint capsule.

Nerves

The subscapularis muscle is innervated by the upper and lower subscapular nerves, which branch from the posterior cord of the brachial plexus (C5-C7). The upper subscapular nerve innervates the cranial half of the muscle, while the lower subscapular nerve supplies the caudal half. The inferior branch of the lower subscapular nerve also innervates the teres major muscle.

Actions

The subscapularis muscle is primarily responsible for internal (medial) rotation of the humerus. When the arm is raised, it draws the humerus forward and downward. It also helps stabilize the humeral head by preventing its anterior displacement.