Axillary Artery

Overview

The axillary artery is the main arterial supply to the upper limb and the walls of the axilla. It is a direct continuation of the subclavian artery, beginning at the lateral margin of rib I and ending at the inferior (lower) border of teres major, where it continues as the brachial artery.

Three parts of the axillary artery, its relation to pectoralis minor, subclavius, and its continuation as the brachial artery

Fig. 7.49 - Parts of the axillary artery (Gray's Anatomy for Students)

Three Parts - Division by Pectoralis Minor

The pectoralis minor muscle crosses the artery anteriorly and divides it into three parts:

Part	Position relative to pectoralis minor	No. of Branches	Branch(es)
1st	Proximal to pectoralis minor	1	Superior thoracic artery
2nd	Posterior to pectoralis minor	2	Thoraco-acromial artery, Lateral thoracic artery
3rd	Distal to pectoralis minor	3	Subscapular artery, Anterior circumflex humeral artery, Posterior circumflex humeral artery

Mnemonic: 1, 2, 3 branches from the 1st, 2nd, 3rd parts respectively.

Branches - Detailed Description

All six named branches of the axillary artery with their muscle relationships

Fig. 7.50 - Branches of the Axillary Artery (Gray's Anatomy for Students)

1st Part Branch

Superior Thoracic Artery

Small vessel arising from the anterior surface of the 1st part
Supplies the upper regions of the medial and anterior axillary walls

2nd Part Branches

Thoraco-acromial Artery

Short trunk arising from the anterior surface of the 2nd part, just posterior to the medial (superior) margin of pectoralis minor
Curves around the superior margin of pectoralis minor, pierces the clavipectoral fascia
Divides into four branches: pectoral, deltoid, clavicular, and acromial
The pectoral branch supplies the breast; the deltoid branch travels in the clavipectoral triangle alongside the cephalic vein

Lateral Thoracic Artery

Arises from the anterior surface of the 2nd part, posterior to the lateral (inferior) margin of pectoralis minor
Follows the muscle margin to the thoracic wall
Supplies the medial and anterior axillary walls
In women, branches wrap around the inferior margin of pectoralis major and supply the breast

3rd Part Branches

Subscapular Artery (largest branch of the axillary artery)

Originates from the posterior surface of the 3rd part
Follows the inferior margin of subscapularis for a short distance, then divides into two terminal branches:
- Circumflex scapular artery - passes through the triangular space (subscapularis, teres major, long head of triceps), enters the infraspinous fossa, and anastomoses with the suprascapular and dorsal scapular arteries - forming the periscapular anastomotic network
- Thoracodorsal artery - follows the lateral border of the scapula to the inferior angle; supplies the posterior and medial axillary walls

Anterior Circumflex Humeral Artery

Small; arises from the lateral side of the 3rd part
Passes anterior to the surgical neck of the humerus
Supplies the glenohumeral joint and head of humerus
Anastomoses with the posterior circumflex humeral artery

Posterior Circumflex Humeral Artery

Larger than the anterior; arises from the lateral surface of the 3rd part, just posterior to the anterior circumflex humeral artery
Exits the axilla through the quadrangular space (teres major, teres minor, long head of triceps brachii, surgical neck of humerus) alongside the axillary nerve
Curves around the surgical neck of humerus; supplies surrounding muscles and the glenohumeral joint
Anastomoses with the anterior circumflex humeral, profunda brachii, suprascapular, and thoraco-acromial arteries

Anatomical Relations

The brachial plexus cords (lateral, medial, posterior) are closely related to the axillary artery - specifically, they are named in relation to the 2nd part of the artery
The axillary artery is accompanied medially and anteriorly by the axillary vein (which becomes the subclavian vein at the lateral margin of rib I)
The artery is enclosed within the axillary sheath along with the brachial plexus

Periscapular Collateral Anastomoses

When the axillary artery is occluded, blood flow is maintained via a rich anastomotic network connecting the 1st segment of the subclavian artery to the 3rd segment of the axillary artery. The arteries forming this network include:

Transverse cervical artery
Dorsal scapular artery
Suprascapular artery
Subscapular artery (via its circumflex scapular branch)

Anatomical Variations

The branching pattern is quite variable, particularly involving the subscapular and posterior circumflex humeral arteries (variation in ~66% of people):

High origin of subscapular artery from the 2nd part (seen in 29-36%)
Common origin of subscapular and posterior circumflex humeral arteries from the 2nd or 3rd part (12-42%)
Axillary origin of the thoracodorsal artery (3-10%)
Early division of the axillary artery into a superficial brachial artery and a deep brachial artery

(Imaging Anatomy: Bones, Joints, Vessels and Nerves)

Clinical Relevance

Anterior Shoulder Dislocation

Anterior dislocation of the humeral head may compress the axillary artery, causing vessel occlusion. This is unlikely to render the limb completely ischemic (due to the collateral network), but surgical reconstruction may be needed for pain-free function. The axillary nerve and brachial plexus are also at risk of injury.

Central Venous Access ("Subclavian" line)

What clinicians commonly call the "subclavian route" for central venous cannulation actually accesses the 1st part of the axillary vein. The puncture should be at or lateral to the midclavicular line to avoid kinking of lines/pacemaker wires by the subclavius muscle.

Axillary Artery as Catheter Access Site

In extensively burned patients (where other arterial sites are unavailable), the axillary artery may be used for arterial cannulation. Caution: air or thrombi flushed retrograde can reach the cerebral circulation, so vigorous flushing must be avoided.

Regional Anaesthesia (Brachial Plexus Block)

With the arm abducted and externally rotated, the axillary artery is easily palpable. This pulsation is used to locate the brachial plexus for axillary nerve blocks, a common approach to upper limb regional anaesthesia. Under ultrasound, successful infraclavicular block is confirmed by "U-shaped" spread of local anaesthetic under the axillary artery and separation of the cords from the vessel wall.

Sources: Gray's Anatomy for Students; Imaging Anatomy: Bones, Joints, Vessels and Nerves (THIEME Atlas); General Anatomy and Musculoskeletal System (THIEME Atlas); Miller's Anesthesia 10e; Morgan & Mikhail's Clinical Anesthesiology 7e

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