Topography and Syntopy
The vessel begins at the lateral border of the first rib (or level of the clavicle) within the clavipectoral triangle (trigonum clavipectorale), where the proximal segment is covered by the subclavius muscle. It terminates at the inferior border of the pectoralis major muscle, beyond which it changes its name to become the brachial artery (a. brachialis).
Along its course, the artery closely relates to other vital structures. The subclavian vein (v. subclavia) lies anterior and medial to it. Additionally, the trunks and cords of the brachial plexus (plexus brachialis) surround the artery at various levels, holding immense clinical significance.
Topographic Parts
For study and surgical navigation, the vessel is divided into three parts using the pectoralis minor muscle (m. pectoralis minor) as the primary landmark:
- Part I — From the first rib/clavicle to the superior border of the pectoralis minor. Here, the artery rests on the first digitation of the serratus anterior, with the clavipectoral fascia anterior to it.
- Part II — Located directly posterior to the pectoralis minor muscle. The cords of the brachial plexus (lateral, medial, and posterior) surround the artery according to their respective names in this segment.
- Part III — From the inferior border of the pectoralis minor to the inferior border of the pectoralis major. Laterally, it is bordered by the coracobrachialis muscle.
Branches of the Axillary Artery
Each part gives off specific branches that supply the surrounding tissues.
Branches of Part I:
- Superior thoracic artery (a. thoracica superior) — Runs medially, supplying the upper two intercostal spaces, serratus anterior, pectoral muscles, and the breast.
- Thoracoacromial artery (a. thoracoacromialis) — Pierces the clavipectoral fascia and immediately divides into four branches: clavicular (to the sternoclavicular joint and subclavius), deltoid (travels in the deltopectoral groove), acromial (contributes to the acromial network), and pectoral branches (supply the pectoral muscles and give lateral branches to the breast).
Branches of Part II:
- Lateral thoracic artery (a. thoracica lateralis) — Descends along the lateral border of the pectoralis minor. It serves as a major blood supply source for the lateral quadrant of the breast and the axillary lymph nodes.
Branches of Part III:
- Subscapular artery (a. subscapularis) — The largest branch. After supplying the subscapularis muscle, it divides into two main vessels: the circumflex scapular artery (a. circumflexa scapulae), which passes posteriorly through the triangular space into the infraspinatous fossa, and the thoracodorsal artery (a. thoracodorsalis), which descends along the lateral chest wall to the latissimus dorsi.
- Anterior circumflex humeral artery (a. circumflexa humeri anterior) — Passes laterally deep to the short head of the biceps brachii and coracobrachialis, encircling the surgical neck of the humerus anteriorly.
- Posterior circumflex humeral artery (a. circumflexa humeri posterior) — Travels posteriorly through the quadrangular space alongside the axillary nerve, encircling the surgical neck of the humerus posteriorly.
Anastomoses and Clinical Significance
Branches of the axillary artery form rich vascular networks, most notably the scapular network (rete scapulare) and acromial network (rete acromiale). The scapular network connects the subclavian and axillary arterial systems. Should the main trunk require ligation, these anastomoses provide collateral blood flow.
In plastic surgery, the thoracodorsal artery plays a vital role as the key axial vessel for the latissimus dorsi flap.
Furthermore, the anterior and posterior humeral circumflex arteries lie in close contact with the surgical neck of the humerus, supplying the shoulder joint capsule. These vessels carry a high risk of injury during shoulder dislocations and fractures.