The teres major is a thick, rounded muscle arising from the inferior scapular angle and inserting alongside the latissimus dorsi on the medial humeral groove, earning it the informal label of the latissimus's little helper. Despite its similar name, it has completely opposite actions to the teres minor, being an internal rotator and adductor rather than an external rotator. It forms the posterior axillary fold alongside the latissimus dorsi.
| Origin | Posterior surface of the inferior angle of the scapula |
|---|---|
| Insertion | Medial lip of the intertubercular groove of the humerus, just medial to the latissimus dorsi insertion |
| Nerve Supply | Lower subscapular nerve (C5, C6, C7) |
| Blood Supply | Circumflex scapular artery |
| Actions | Adduction of the arm at the shoulder; Internal rotation of the arm; Extension of the arm from a flexed position |
|---|
It assists the latissimus dorsi in pulling the arm downward and backward from an elevated position, contributing to the power of pulling and climbing movements and providing dynamic stability to the inferior glenohumeral joint capsule.
The teres major is a significant contributor to the posterior axillary fold and is reliably palpable there during clinical assessment. In overhead throwing athletes, tightness in the teres major combined with posterior capsule contracture contributes to glenohumeral internal rotation deficit, which is associated with labral tears and posterior shoulder instability. The muscle is innervated by the lower subscapular nerve, making it a test muscle for this nerve's integrity.
With the arm abducted to 90 degrees and internally rotated against resistance, the teres major can be felt as the lower of the two muscles forming the posterior axillary fold, below the teres minor and distinctly thicker.
Acute tear from forceful internal rotation or adduction against resistance, producing posterior axillary pain that worsens with reaching overhead or across the body and can be confused with posterior glenohumeral joint pathology.
