Pectoralis Major Anatomy

The pectoralis major is a large fan-shaped muscle covering the anterior chest wall, arising from the clavicle, sternum, costal cartilages and external oblique aponeurosis, and converging on a short flat tendon at the lateral lip of the bicipital groove. Its surgical importance is concentrated in four areas: it forms the medial wall of the deltopectoral interval, it ruptures in a characteristic and increasingly common pattern in weight-training athletes, it is the standard transfer for irreparable subscapularis insufficiency, and it is the muscle congenitally absent in Poland syndrome.

The anatomy that unlocks all four is the same: a bilaminar tendon that twists. Grasping which fibres end up where at the insertion explains why the inferior lamina fails first, why a partial rupture can look like a complete one clinically, why the sternal head is chosen for transfer, and why the repair must reconstruct a footprint rather than simply reattach a stump.

Actions by head

Whole-muscle function

• Adduction and internal rotation are the dominant actions, working with latissimus dorsi, teres major and subscapularis.
• Antagonistic heads. From a position of full flexion the sternocostal head extends the arm back to the side, while the clavicular head flexes it. The two heads therefore oppose one another through part of the arc, which is why they can be separately tested.
• Depression of the shoulder girdle with a fixed humerus, contributing to trunk elevation in climbing and to crutch walking.
• Accessory respiration: with the arms fixed, the muscle elevates the ribs — the reason a breathless patient braces the arms on a table.

Strength and rupture mechanics

• Loss of the pectoralis major reduces adduction and internal rotation power by roughly a quarter to a half in objective testing, with the greater deficits at higher speeds and in the horizontal adduction vector.
• Peak tendon strain occurs in the abducted, extended and externally rotated position under eccentric load. The bench press descent reproduces this exactly, which is why bench pressing accounts for the majority of ruptures. Anabolic steroid use is a recognised association.
• Because of the tendon twist, strain concentrates on the inferior lamina, so ruptures propagate from inferior to superior.

Synergists and antagonists

• Synergists: latissimus dorsi, teres major, subscapularis (adduction and internal rotation), anterior deltoid (flexion and horizontal adduction), coracobrachialis.
• Antagonists: deltoid and supraspinatus (abduction), infraspinatus and teres minor (external rotation), trapezius and serratus anterior (girdle elevation).

Palpation and positioning

• The anterior axillary fold is the lateral border of pectoralis major and is the structure to inspect and palpate. Ask the patient to press the palms together in front of the chest, or to push the hands into the hips, and compare the folds.
• The clavicular head is isolated by resisted forward flexion at about 90 degrees; the sternocostal head by resisted adduction from an abducted position or resisted extension from flexion.
• Inspect from the front with the arms at the side, then with the arms elevated, and then during resisted adduction. A partial sternal head rupture may be visible only in one of these positions.
• Look for the medially retracted muscle bulge and the thinning of the axillary fold — the two together are more reliable than either alone.

Named tests and clinical assessment

Musculocutaneous nerve injury

• Mechanism: transfer forced through a tight subcoracoid tunnel, forceful medial retraction of the conjoined tendon, or dissection deep to the coracoid without identifying the nerve.
• Consequence: loss of elbow flexion power and numbness over the lateral forearm — a poor exchange for improved internal rotation.
• Avoidance: identify the nerve, create the tunnel bluntly, retract gently and intermittently, and choose the superficial route if the window is tight.

Failure of a rupture repair

• Re-rupture is uncommon after acute anatomic repair but rises steeply in chronic tears requiring graft reconstruction and in patients who return to heavy bench pressing too early.
• Inadequate footprint restoration: fixing the tendon as a point rather than restoring the 5 cm footprint gives weaker fixation and poorer strength recovery.
• Failure to restore the twist: reducing the inferior lamina to the inferior footprint leaves the repair mis-tensioned.
• Avoidance: repair acutely wherever possible, restore the broad footprint, respect the lamina anatomy, and protect for six weeks.

Humeral shaft fracture

• A recognised complication of large bicortical drill holes at the level of the pectoralis insertion, either at rupture repair or at subpectoral biceps tenodesis.
• Avoidance: unicortical fixation, small-diameter implants, and avoiding multiple closely spaced holes.

Nerve injury to the muscle itself

• Lateral pectoral nerve injury from aggressive medial retraction in the deltopectoral approach; medial pectoral nerve injury during pectoralis minor tenotomy, since that nerve pierces the muscle.
• Because of the ansa pectoralis and the separate supply to each head, partial denervation is more common than complete, producing a segmental contour defect.

Transfer-specific problems

• Loss of internal rotation is not always restored: the pectoralis vector is a compromise, and patients should be counselled that pain relief and improvement in activities of daily living are more reliable than restoration of power.
• Anterior overtightening limits external rotation.
• Failure of re-education: the patient must learn to fire the transfer in a new role.
• Poor outcome with a concomitant irreparable supraspinatus, shown clearly in published series.

Flap complications

• Bulk and tethering in head and neck reconstruction, and a visible chest wall contour defect and loss of the anterior axillary fold in women in particular.
• Distal flap necrosis where the skin paddle is placed beyond the reliable territory of the thoracoacromial pedicle.
• Loss of the muscle as a future donor once it has been used.

Related pages. When it tears: Pectoralis Major Rupture is the dedicated injury page for the classification and repair discussed above. What it is transferred to replace: Subscapularis Anatomy and Subscapularis Tears - and note the selection rule is set by the supraspinatus, so read Massive Rotator Cuff Tears, Rotator Cuff Tears and Rotator Cuff Arthropathy before promising a transfer. The nerve the subcoracoid route threatens: Musculocutaneous Nerve Anatomy, and Latarjet Procedure, which is where the disputed 5 cm safe zone came from. Its neighbours and the other transfer options: Pectoralis Minor, Latissimus Dorsi, Serratus Anterior and Brachial Plexus Anatomy. Structures it attaches to or crosses: Clavicle Fractures, Sternoclavicular Joint Injuries and Biceps Tendon Pathology, the groove its bilaminar tendon flanks.

Pectoralis major rupture

Repair technique

Poland syndrome

Other clinical entities

Pectoralis major transfer for subscapularis insufficiency

The deltopectoral approach

• Internervous plane: pectoralis major (medial and lateral pectoral nerves) medially and deltoid (axillary nerve) laterally — a true internervous plane and the workhorse anterior approach to the shoulder.
• Landmarks: the incision runs from just lateral to the coracoid toward the deltoid insertion. The cephalic vein marks the interval and is usually retracted laterally with the deltoid, since most of its tributaries come from the deltoid side.
• Clavipectoral fascia is incised lateral to the conjoined tendon; the conjoined tendon is retracted medially, gently, to protect the musculocutaneous nerve.
• The upper 1 to 2 cm of the pectoralis major insertion may be released to improve exposure of the humeral shaft and is repaired at closure.
• The three sisters, the anterior circumflex humeral vessels, mark the inferior border of subscapularis and are ligated in an extensile exposure.

Subpectoral biceps tenodesis

• The inferior border of pectoralis major is the landmark, with the tenodesis performed just proximal to it in the bicipital groove where the biceps tendon lies immediately deep to the pectoralis tendon.
• Structures at risk: cadaveric work places the musculocutaneous nerve roughly 3 cm medial to the tenodesis site and the radial nerve a similar distance distal and posterior; the axillary nerve lies proximally.
• Humeral shaft fracture through a large bicortical drill hole at this level is a recognised complication; use unicortical fixation or a small-diameter implant.

Flap use

• Pedicled myocutaneous flap on the thoracoacromial pectoral branch for head and neck reconstruction.
• Turnover flap on internal thoracic perforators for post-sternotomy sternal wound coverage.
• Deltopectoral fasciocutaneous flap on the same perforators.
• The Mathes-Nahai Type V pattern is what permits both directions.

Anatomical variation across populations

• The sternalis muscle, a longitudinal slip lying anterior to the sternal origin of pectoralis major, is present in a minority of individuals with reported prevalence differences across populations and between the sexes. It is clinically irrelevant except as a cause of confusion on mammography and as an unexpected finding at surgery.
• The abdominal head derived from the external oblique aponeurosis is variably developed, which affects the amount of low-origin muscle available for transfer.
• The entry point of the musculocutaneous nerve into coracobrachialis is genuinely variable, and a proportion of specimens have proximal branches close to the coracoid. This variation, not a measurement error, is why the safe zone is a guide rather than a rule.
• Poland syndrome occurs sporadically worldwide with a reported incidence in the order of one in 20,000 to 30,000 births and a consistent right-sided and male predominance across reported series.

Side-by-side guidance

Registry and outcome signals

• Pectoralis major rupture repair is not captured by joint registries. The evidence base is pooled case series and systematic reviews, and the consistent signal across them is that operative treatment outperforms non-operative treatment in active patients and that acute repair outperforms delayed repair.
• Reported incidence of rupture has risen over recent decades in parallel with recreational and competitive weight training, and this is a consistent international trend rather than a local one.
• Tendon transfers for subscapularis insufficiency are low-volume procedures without registry coverage; institutional series consistently show reliable pain relief, variable strength recovery, and a strong negative effect of concomitant irreparable supraspinatus disease.
• Reverse arthroplasty volumes continue to grow in every national registry, and in older patients a reverse has largely displaced transfer for anterosuperior cuff insufficiency.

High-resource versus limited-resource practice

• Well-resourced settings: MRI in the abducted externally rotated position for rupture characterisation, suture button and anchor fixation, arthroscopically assisted transfer, and free tissue transfer as the reconstructive first choice.
• Limited-resource settings: transosseous bone trough repair of a ruptured tendon achieves comparable results with no implant cost, and the pedicled pectoralis major flap remains one of the most valuable reconstructive operations available anywhere, requiring no microsurgery.
• The universally applicable clinical skill is separate testing of the two heads, which costs nothing and prevents the commonest diagnostic error — missing a sternal lamina rupture behind an intact clavicular head.