Teres major muscle
The teres major is a thick muscle of the shoulder joint. It spans from the inferior aspect of the scapula to the proximal part of the humeral shaft. Unlike the teres minor, the teres major muscle does not attach to the capsule of the glenohumeral joint. Thus it is not regarded as part of the rotator cuff muscles.
The main function of this muscle is to produce movements of the arm on the shoulder joint. By contracting, it pulls the humerus posteriorly (extension) and rotates it medial towards the trunk (internal rotation). Additionally, it contributes to the stabilization of the shoulder joint.
In this article, we will discuss the anatomy and function of the teres major muscle.
|Origins||Inferior angle and lower part of the lateral border of the scapula|
|Insertions||Intertubercular sulcus (medial lip) of the humerus|
|Innervation||Lower subscapular nerve (C5-C7)|
|Blood supply||Thoracodorsal branch of subscapular artery and posterior circumflex humeral artery|
|Function||Extension and internal rotation of the humerus (arm)|
Origin and insertion
The teres major muscle originates from the posterior surface of the inferior angle of scapula, as well as from the lower part of the lateral border of the scapula. At its origin, the muscle is easily palpated and felt like a soft tissue structure on the inferior scapular angle.
The muscle fibers course spirally (torsion), running parallel to the fibers of the latissimus dorsi muscle. They converge onto a single tendon that inserts to the intertubercular sulcus (medial lip) of the humerus.
The posterior aspect of the scapular portion of teres major is covered by the teres minor and infraspinatus muscles. The anterior aspect of teres major is in relation with the subscapularis muscle.
The inferior margin of teres major is parallel to the superior border of the latissimus dorsi muscle. The adjoining fibers of these two muscles may be fused in some individuals. Along with the teres minor muscle, teres major forms the posterior axillary fold. Sometimes their muscle bellies or insertion tendons even blend with one another.
The innervation of the teres major muscle is supplied by the lower subscapular nerve (C5-C7) a branch of the brachial plexus.
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The main function of teres major is to produce the movements of the humerus at the glenohumeral joint; it pulls the anterior surface of the humerus medially towards the trunk (internal rotation). Furthermore, it can extend the arm from the flexed position.
Along with the pectoralis major and latissimus dorsi muscles, teres major can pull the trunk superiorly (through adduction) when its humeral attachment is fixed. This is why it is also referred to as the climbing muscle. Additionally, it contributes to the stabilization of the shoulder joint.
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 microtraumas 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.