Axillary Artery

Introduction

Introduction to the Axillary Artery

The axillary artery is the principal vascular channel conveying oxygenated blood to the upper limb. Arising as the direct continuation of the subclavian artery at the outer border of the first rib, it traverses the axilla before transitioning into the brachial artery at the inferior border of the teres major muscle. Throughout its course, it establishes crucial relationships with the cords and branches of the brachial plexus and serves as the architectural core of the axilla. Understanding its anatomy, division into three distinct parts relative to the pectoralis minor muscle, and branch distribution patterns is essential for surgical procedures in the pectoral region, axillary dissections, and managing trauma to the upper extremity.

Study

Course, Relations, and Subdivisions

The axillary artery begins at the lateral border of the 1st rib and ends at the inferior border of the teres major muscle. It is anatomically divided into three segments by the pectoralis minor muscle, which crosses anterior to the artery. The first part is proximal to the pectoralis minor, the second part lies posterior to it, and the third part is distal to its lateral border. A classic anatomical mnemonic to recall the branches corresponding to each part is: 1st part has 1 branch, 2nd part has 2 branches, and 3rd part has 3 branches.

Detailed Branches by Segment

First Part (1 branch): The Superior Thoracic Artery (highest thoracic artery) is a small vessel that arises near the subclavius muscle. It runs anteromedially along the upper border of the pectoralis minor to supply the first two intercostal spaces, the superior part of the serratus anterior, and overlying pectoral muscles. Second Part (2 branches): 1. The Thoracoacromial Artery (thoracoacromial trunk) emerges at the medial border of the pectoralis minor, pierces the clavipectoral fascia, and immediately divides into four regional branches: pectoral, acromial, clavicular, and deltoid branches (Mnemonic: ABCD - Acromial, Breast/Pectoral, Clavicular, Deltoid). 2. The Lateral Thoracic Artery arises near the lateral border of the pectoralis minor, tracks downward along the serratus anterior muscle, and gives off substantial lateral mammary branches to the breast. Third Part (3 branches): 1. The Subscapular Artery is the largest branch of the axillary artery. It passes inferiorly along the subscapularis muscle and splits into the circumflex scapular artery (which passes through the upper triangular space to participate in the scapular anastomosis) and the thoracodorsal artery (which accompanies the thoracodorsal nerve to supply the latissimus dorsi). 2. The Anterior Circumflex Humeral Artery is a small branch that winds anteriorly around the surgical neck of the humerus. 3. The Posterior Circumflex Humeral Artery is a much larger branch that passes posteriorly through the quadrangular space alongside the axillary nerve to anastomose with the anterior circumflex branch, supplying the deltoid muscle and glenohumeral joint.

Clinical Correlations and Scapular Anastomosis

The scapular arterial anastomosis forms a vital collateral pathway. If the subclavian or proximal axillary artery is ligated or occluded, blood flow can reverse through this network to supply the distal limb. It links branches of the thyrocervical trunk (suprascapular and transverse cervical arteries) with the circumflex scapular and thoracodorsal branches of the subscapular artery. Crucially, ligation of the axillary artery between the thyrocervical trunk origins and the subscapular artery allows collateral flow to persist. However, ligation proximal to the brachial artery and distal to the subscapular artery completely isolates the upper limb from this collateral supply, causing acute ischemia. Furthermore, the proximity of the third part of the axillary artery to the surgical neck of the humerus subjects it to a high risk of laceration or occlusion during anteroinferior glenohumeral dislocations or displaced humeral fractures.

Summary

Key Summary Points

• Extent: Extends from the lateral border of the 1st rib to the inferior border of the teres major muscle. • Divisions: Separated into 1st, 2nd, and 3rd parts by the pectoralis minor muscle. • Branch Distribution: 1st part yields 1 branch (superior thoracic); 2nd part yields 2 branches (thoracoacromial, lateral thoracic); 3rd part yields 3 branches (subscapular, anterior circumflex humeral, posterior circumflex humeral). • Scapular Anastomosis: Connects the thyrocervical trunk (subclavian branch) to the subscapular artery (axillary branch), preserving upper limb perfusion during proximal vascular blocks. • Vulnerabilities: The third part is highly susceptible to trauma during surgical neck humerus fractures and shoulder dislocations because it runs alongside the axillary nerve in close proximity to the humerus bone.