Subscapularis Muscle Anatomy

The subscapularis muscle forms the largest component of posterior wall of the axilla and this muscle is covered by a dense membrane (dense fascia) which is attached to the scapula at the margins of its origin. Subscapularis is part of the SITS muscles or the rotator cuff muscles of which their primary function during all movements of the glenohumeral joint (shoulder joint) is to hold the humeral head in the glenoid cavity of the scapula. The other rotator cuff muscles are the supraspinatus, infraspinatus and teres minor.

The subscapularis tendon is separated from a bare area at the lateral angle of the scapula by a bursa known as the Subscapular bursa that communicates with the cavity of the shoulder joint. This subscapular bursa extends laterally and communicates with the cavity of the shoulder joint through a gap in the anterior part of its capsule between the superior and middle glenohumeral ligaments.

Subscapularis Origin and Insertion

Subscapularis originates from the subscapular fossa that is located on the anterior surface of the scapula specifically arising from the medial two-thirds of the costal surface of the scapula and also from the inter-muscular septa which raise ridges on the scapula. This fossa occupies most of the anterior surface of the scapula. The subscapularis tendon crosses immediately to the joint capsule of the glenohumeral joint to insert on the lesser tubercle of humerus.

Subscapularis Muscle Action and Function

The function of subscapularis muscle is to medially rotate and adduct the arm. Because it is part of the rotator cuff muscles, it also stabilizes the shoulder joint by holding the head of the humerus in the glenoid cavity.

Subscapularis Nerve Supply

The upper and lower subscapular nerves derived from the C5, C6 and C7 cervical segments of the spinal cord C6 being the main segmental innervation. These two nerves that supply the subscapularis are branches from the posterior cord of the brachial plexus.

Subscapularis Muscle Blood Supply

The blood supply of the subscapularis is from the subscapular artery which is the largest branch of the axillary artery. The subscapular vein drains blood away from the subscapularis muscle into the axillary vein.

Subscapularis Test

There is no satisfactory test for subscapularis muscle because its action is difficult to differentiate from other medial rotators of the arm.