Teres major is a thick and oval-shaped muscle that lies in the upper arm. Although having similar names, Teres major is different in terms of actions and innervation when compared to the teres minor. It’s main function is to facilitate medial rotation of the arm and it also helps in maintaining static posture and arm-swinging.
Origin and Insertion
The teres major muscle has two origins. One is at the dorsal surface of the inferior angle and another one is from the lower part of the lateral border of the scapula. where it can be easily palpated. It turns from there in a spiral manner, runs parallel to the fibers of the latissimus dorsi and at the crest of the lesser tubercle of the humerus, it inserts together with its “big brother”.
In their course, posterior axillar fold is formed by both the muscles. Sometimes their muscle bellies or insertion tendons mix into one another. It does bot attach to the glenohumeral joint’s capsule unlike the teres minor. Therefore it can’t be treated as part of the rotator cuff.
Either the lower scapular nerve (C5-C8) or thoracodorsal nerve (C5-C7) supply the innervation of the teres major muscle.
There are three movements in the shoulder joint that Teres major is responsible for:
- First is due to its insertion at the anterior side of the humerus, it turns the humerus medially which is what we call inward rotation.
- It also pulls the humerus in the direction of the trunk which is known as adduction
- And another one is from behind which is called retroversion.