Hi, everyone! It’s Matt from Kenhub, and in this tutorial, we will discuss the origin, insertion, innervation, and function of the teres major muscle.
The teres major muscle is a thick muscle of the shoulder joint. 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.
It originates at the dorsal surface of the inferior angle and the lower part of the medial border of the scapula, where it is easily palpated. From there, it turns spirally, which is known as torsion.
This muscle has a close relationship with the latissimus dorsi muscle. It 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 axillary fold. Sometimes, their muscle bellies or insertion tendons even blend together, and their motions in the shoulder joint are basically identical.
The innervation of the teres major muscle is supplied by either the lower scapular nerve or thoracodorsal nerve, 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, which is known as inward rotation.
Furthermore, it pulls the humerus towards the trunk, known as adduction, and behind, known as retroversion.
In case of a fixed humerus, the contraction of the muscle leads to a craniolateral movement of the inferior angle of the scapula, known as rotation.