Teres major muscle
Anatomy and supply
The Teres major is a thick muscle of the shoulder joint. It originates at the dorsal surface of the inferior angle and the lower part of the lateral border of the scapula, where you can easily palpate it. From there it turns spirally (torsion), runs parallel to the fibers of the latissimus dorsi and inserts together with its' “big brother” at the crest of the lesser tubercle of the humerus. During their course, both muscles form the posterior axillar fold. Sometimes their muscle bellies or insertion tendons even blend in one another. Unlike the Teres minor, the Teres major does not attach to the capsule of the glenohumeral joint. Thus it is not regarded as part of the rotator cuff. The innervation of the Teres major muscle is supplied by either the lower scapular nerve (C5-C8) or thoracodorsal nerve (C5-C7), both branches of the brachial plexus.
The Teres major causes three movements in the shoulder joint: Due to its insertion at the anterior side of the humerus, it turns the humerus medially (inward rotation). Furthermore, it pulls the humerus towards the trunk (adduction) and behind (retroversion). In case of a fixed humerus the contraction of the muscle leads to a craniolateral movement of the inferior angle of the scapula (rotation). As the fibers of both the Latissimus dorsi and Teres major run parallel, their motions in the shoulder joint are basically identical.
The Teres major is relatively prone to the development of trigger points. These are local, permanent hypertensive areas with rigidification (myofascial pain syndrome). Common causes are poor stretching before physical activities, trauma (e.g. fall on the shoulder) and microtraumata through chronic inappropriate straining. Symptoms include local pain, which may radiate to the lateral shoulder during palpation and difficulties in abducting and elevating the arm.