Anatomy Atlas

Pectoralis major

Musculus pectoralis major
MuscledraftMSK

Large fan-shaped muscle of the anterior chest that adducts and medially rotates the arm. It forms the anterior axillary fold and lies deep to the breast.

Core anatomy

Location

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

Group

Anterior axioappendicular (pectoral) muscles.

Origin

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

Insertion

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

Innervation

Lateral and medial pectoral nerves (clavicular head mainly C5–C6; sternocostal head C7, C8, T1) verify

Blood supply

Pectoral branches of the thoracoacromial artery (from the axillary artery), with contributions from perforating branches of the internal thoracic artery.

Action
  • Adducts and medially rotates the humerus
  • The clavicular head flexes the arm; the sternocostal head extends it from a flexed position
  • Draws the scapula anteriorly and inferiorly (with the arm fixed, acts as an accessory muscle of inspiration)
Relations

Its inferolateral border forms the anterior axillary fold. The breast lies on the pectoral fascia, separated by the retromammary space. The deltopectoral groove (cephalic vein) separates it from deltoid. Pectoralis minor lies deep to it.

Mentioned in

Generated automatically from links in other entries.

Pectoralis major converging on the humerus, with deltoid, biceps brachii and the deltopectoral groove
Pectoralis major converging on the lateral lip of the bicipital groove.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 410. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Pectoralis major tendon rupture

Mechanism / lesion

Eccentric overload, classically during bench pressing, usually in young men (anabolic steroid use is a risk factor).

Classic presentation

Sudden pain and a pop at the anterior shoulder, bruising of the arm and chest, loss of the anterior axillary fold contour, and weak adduction and internal rotation.

Poland syndrome

Mechanism / lesion

Congenital unilateral absence of the sternocostal head of pectoralis major.

Classic presentation

Chest wall asymmetry, often with an ipsilateral hand anomaly (syndactyly or brachydactyly) and breast/nipple hypoplasia.

Breast cancer fixation to the pectoral fascia PANCE

Mechanism / lesion

Infiltration of the retromammary space and pectoral fascia by a deep breast carcinoma.

Classic presentation

The breast mass moves with contraction of pectoralis major (tested with the hands pressed on the hips). Fixation indicates deeper invasion.

High-yield PANCE pearls

  • Pectoralis major = adduction + medial rotation; lateral and medial pectoral nerves.
  • Bench-press injury with loss of the anterior axillary fold → pectoralis major rupture.
  • During breast exam, have the patient press hands on hips to contract pectoralis and reveal fixation or dimpling.

Imaging anatomy

X-ray

Absence of the muscle (Poland syndrome) can make one hemithorax appear hyperlucent on CXR.

MRI

MRI defines the site of rupture (musculotendinous junction vs tendon avulsion from the humerus) and retraction.

Ultrasound

Dynamic assessment of tendon continuity at the humeral insertion.

Physical exam

Surface landmarks

The anterior axillary fold. The clavicular and sternocostal heads are visible on resisted adduction.

Palpation

Palpate the anterior axillary fold bilaterally while the patient presses the palms together in front of the chest.

Strength / function testing

Resisted adduction and medial rotation. Resisted adduction from 90° flexion (clavicular head) vs from 60° abduction (sternocostal head).

Self-quiz

Q1.

A 28-year-old weightlifter felt a pop in his right anterior shoulder while bench pressing. He has bruising and loss of the anterior axillary fold. Which action is weakest?

Show answer

C

Pectoralis major rupture weakens adduction and medial (internal) rotation of the humerus. It forms the anterior axillary fold.

Q2.

Pectoralis major inserts onto which part of the humerus?

Show answer

C

Pectoralis major inserts on the lateral lip of the intertubercular groove. Latissimus dorsi inserts in the floor and teres major on the medial lip ("a lady between two majors").

Q3.

During a breast exam, the patient presses her hands firmly on her hips. What is the purpose of this maneuver?

Show answer

B

Pressing on the hips contracts pectoralis major. Skin dimpling or a mass that moves with the muscle suggests malignancy tethering suspensory ligaments or fixing to the pectoral fascia.

Flashcards

See also