Pectoralis major

Musculus pectoralis major

Also known as: pecs, pectoral muscle

A large, fan-shaped muscle of the anterior chest with clavicular and sternocostal heads. It adducts and medially rotates the humerus, flexes it (clavicular head) and extends it from flexion (sternocostal head).

Overview

Pectoralis major has two heads. The clavicular head arises from the medial half of the clavicle. The larger sternocostal head arises from the anterior sternum, the costal cartilages of ribs 1–6 and the aponeurosis of the external oblique. The fibres converge into a flat bilaminar tendon that inserts on the lateral lip of the intertubercular sulcus. The tendon twists so that the lowest sternocostal fibres insert highest and form the rounded anterior axillary fold. A groove between the clavicular head and deltoid (the deltopectoral groove, widening into the clavipectoral triangle) carries the cephalic vein.

As a whole, the muscle adducts and medially rotates the humerus. The clavicular head flexes the arm, from extension up to about 90°. The sternocostal head extends the flexed arm back to the side, as in pushing down or climbing. With the arm fixed, it pulls the trunk toward the arm and can act as an accessory muscle of inspiration. Its innervation comes from both pectoral nerves: the lateral pectoral nerve (C5–C7) mainly supplies the clavicular head, and the medial pectoral nerve (C8–T1) the sternocostal head after piercing pectoralis minor.

Location

Anterior chest wall, deep to the breast, forming the anterior wall of the axilla.

Parts & subdivisions

Clavicular head

From the medial half of the clavicle. Flexes the humerus. Supplied by the lateral pectoral nerve (C5–C6).

Sternocostal head

From the sternum, costal cartilages 1–6 and the external oblique aponeurosis. Extends the flexed humerus. Supplied by the medial and lateral pectoral nerves (C7–T1).

Abdominal part

A small slip from the external oblique aponeurosis.

Anatomy

Origin

Clavicular head: anterior surface of the medial half of the clavicle. Sternocostal head: anterior surface of the sternum, costal cartilages 1–6 and the aponeurosis of the external oblique.

Insertion

Lateral lip of the intertubercular sulcus (crest of the greater tubercle) of the humerus.

Action

Adduction and medial rotation of the humerus; flexion (clavicular head) and extension from flexion (sternocostal head).

Innervation

Lateral pectoral nerve (lateral cord) and medial pectoral nerve (medial cord).

Nerve roots

C5–T1 (clavicular head C5–C6; sternocostal head C7–T1)

Arterial supply

Pectoral branch of the thoraco-acromial trunk; perforating branches of the internal thoracic artery; lateral thoracic artery.

Relations

Lies deep to the breast in the retromammary space, on the pectoral fascia. Covers pectoralis minor, the clavipectoral fascia and the axillary vessels. The cephalic vein runs in the deltopectoral groove.

Clinical significance

Pectoralis major rupture

Usually in weightlifters during eccentric bench press, typically as a tendon avulsion from the humerus. It causes bruising, a defect in the anterior axillary fold and weak adduction and medial rotation. Surgical repair is recommended in active patients.

Poland syndrome

Congenital absence of the sternocostal head of pectoralis major, often with syndactyly or a hypoplastic hand on the same side.

Breast cancer fixation

Tumour invading the pectoral fascia becomes fixed when pectoralis major contracts (hands pressed on the hips). This changes surgical planning.