The teres major is sometimes called 'lat's little helper' because it shares the bicipital groove insertion with the latissimus dorsi and acts in parallel — both internally rotate, adduct, and extend the shoulder. It forms the posterior axillary fold alongside the lat. The quadrilateral space (between teres major inferiorly, teres minor superiorly, long head of triceps medially, and the humerus laterally) is traversed by the axillary nerve and posterior circumflex humeral artery.
| Origin | Oval area on the lower third of the posterior scapular lateral border and inferior angle |
|---|---|
| Insertion | Medial lip of the bicipital (intertubercular) groove — shared with the latissimus dorsi |
| Nerve Supply | Lower subscapular nerve (C5, C6, C7) |
| Blood Supply | Circumflex scapular artery |
| Actions | Internal rotation of the shoulder; Adduction of the shoulder; Extension of the shoulder from the flexed position |
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The quadrilateral space is bounded inferiorly by the teres major — quadrilateral space syndrome from compression of the axillary nerve produces posterior shoulder pain and lateral arm numbness. Teres major tendon tears from water polo and throwing sports produce posterior axillary fold pain with internal rotation weakness. The posterior axillary fold palpation test reproduces pain in teres major pathology.
The teres major forms the palpable posterior axillary fold tendon, distinguishable from the latissimus dorsi by its origin on the inferior lateral scapula rather than the thoracolumbar fascia.
Posterior axillary fold tendon disruption in water polo and throwing athletes producing internal rotation weakness managed with physiotherapy or surgical repair.
