Teres Major Muscle Anatomy

Location & Overview

The teres major is a muscle characterised by its thick, rectangular, and somewhat flat shape. It is situated in the shoulder region, extending from the scapula to the humerus. This muscle is found just below the infraspinatus and teres minor muscles, both of which are part of the rotator cuff. However, despite its proximity, the teres major is not considered a component of the rotator cuff. Even so, it still plays an important role in the movements and stability of the shoulder joint.^[1,2,3]

The teres major is located just superior to the latissimus dorsi muscle, and these two muscles often work synergistically in extending, adducting, and internally rotating the humerus.^[4] Therefore, the teres major is occasionally referred to as the “lat’s little helper”.

In the broader context of the muscular system, the teres major is one of seven scapulohumeral muscles. These muscles, which include the teres major, are closely associated with the movement and stabilisation of the shoulder joint. The other scapulohumeral muscles are the deltoid, coracobrachialis, infraspinatus, subscapularis, supraspinatus, and teres minor.^[1,3]

Origin & Insertion

The teres major muscle originates on the posterior surface of the inferior angle of the scapula and inferior part of the lateral border of the scapula (aka the shoulder blade).^[5,4]

The teres major inserts at the medial lip of the intertubercular groove of the humerus. The muscle travels anterior to the triceps long head before attaching to the humerus.^[1,5] The intertubercular groove is a prominent groove that runs vertically down the upper part of the humerus bone. This groove is also known as the ‘bicipital groove’, and it is where the long tendon of the biceps brachii passes through.^[4]

Action & Function

The teres major performs several actions at the shoulder. Its primary roles include extending, medially rotating, and adducting the humerus, or in simpler terms, moving the arm back, rotating it inward, and pulling it towards the body’s midline.^[5,6]

The teres major also plays an important role in stabilising the humeral head, preventing its subluxation or partial dislocation. In carrying out these actions, the teres major often works in synergy with the latissimus dorsi muscle.^[5,6]

Innervation

The teres major is innervated by the lower subscapular nerve, which originates from the nerve roots of C5, C6, and C7. This nerve branches from the brachial plexus and is responsible for transmitting nerve signals between the teres major and the central nervous system, enabling the muscle to contract. The lower subscapular nerve also innervates the subscapularis muscle.^[4,7,6]

Blood Supply

The teres major’s blood supply is primarily provided by the posterior circumflex humeral artery and the thoracodorsal branch of the subscapular artery. The posterior circumflex humeral artery arises from the third, most distal, portion of the axillary artery, travels posteriorly through the quadrangular space, and supplies blood to the teres major, teres minor, deltoid, and long head of the triceps.^[4,6]

The subscapular artery, a large branch of the axillary artery, gives rise to the thoracodorsal artery. This artery supplies blood to the teres major, among other muscles, including the subscapularis and latissimus dorsi.^[4,6] These arteries ensure the teres major muscle receives the necessary oxygen and nutrients to function effectively.