The axillary artery is a large muscular vessel that travels through the axilla. It is responsible for carrying oxygen-rich blood to the upper limb, as well as to parts of the musculocutaneous system of the scapula and upper lateral thorax.
The neurovascular bundle formed by the artery and the cords of the brachial plexus are enveloped by the axillary fascia. The fascia is then attached to the suspensory ligaments of the axilla (a continuation of the clavipectoral fascia) for additional protection. As a result of this attachment, the axillary artery is more easily palpated in the concavity of the axilla when the upper arm is adducted (close to the midline of the body) and the suspensory ligaments are relaxed, than when it is abducted (away from the midline of the body) and the suspensory ligaments are taut.
The axillary artery is a continuation of the subclavian artery that begins at the outer border of the first rib. It then courses through the axilla while being bordered by the lateral (superiorly), posterior (posteriorly), medial (inferiorly) cords of the brachial plexus and the ansa pectoralis (anteriorly).
As it passes through the axilla, the artery is divided into three parts by pectoralis minor, as the muscle travels superolaterally from its origin at the 3rd, 4th and 5th ribs to its insertion on the medial aspect of the coracoid process. Conveniently, each segment gives off a corresponding number of branches. One branch leaves the first segment above, two branches from the second segment beneath and three branches leave the third segment below (all relative to pectoralis minor). While exiting the axilla, the axillary artery changes its name at the lower border of teres major and continues in the arm as the brachial artery.
Superior Thoracic Artery
The superior (highest) thoracic artery is the first branch of the axillary artery. It is given off proximal to the outer border of the anterior scalene muscle. It forms part of the arterial supply to the pectoral muscles.
The second part of the axillary artery gives rise to two vessels. The thoracoacromial (acromiothoracic) artery is a primary trunk that gives rise to four other arteries. By way of its branches, the thoracoacromial artery pierces the clavipectoral fascia to supply regions of the upper limb and trunk for which they are named.
- The clavicular branch courses superomedially towards the sternoclavicular joint where it supplies the joint and subclavius muscle.
- The pectoral branch travels inferomedially toward the pectorales muscles where it provides oxygenated blood to the muscles and the mammaries.
- The acromial branch crosses the medial border of the coracoid process, deep to the deltoid muscle. After supplying this muscle, it pierces it to reach the acromion, where it joins the acromial anastomosis.
- Finally, the deltoid (humeral) branch courses over the tendon over pectoralis minor, then through the deltopectoral groove (with the cephalic vein). Along this course, it supplies both pectoralis major and the deltoid muscle.
Lateral Thoracic Artery
The other branch of the second part of the axillary artery is the lateral thoracic artery. It travels inferomedially along the inferior margin of pectoralis minor. It carries oxygenated blood for the:
- serratus anterior
- pectorales muscles
- subscapularis muscle
The third part of the axillary artery first gives off the subscapular artery, which is the largest branch of the axillary artery. The subscapular artery travels caudally, shortly after which it bifurcates to give the circumflex scapular artery and the thoracodorsal artery.
The circumflex scapular artery courses around the lateral border of the scapula through the (upper) triangular space to enter the infraspinatus fossa. Here it joins the scapular anastomosis. The thoracodorsal artery continues inferiorly alongside the thoracodorsal nerve to supply the latissimus dorsi muscle. The thoracodorsal branch of the subscapular artery forms an anastomosis with the pectoral branch of the thoracoacromial artery, the internal intercostal and the internal mammary arteries.
Circumflex Humeral Arteries
Finally, the third part of the axillary artery gives off an anterior and a posterior circumflex humeral artery (ACHA & PCHA, respectively). The ACHA is the smaller of the two arteries. It travels in a horizontal manner towards the surgical neck of the humerus, deep to the short head of biceps brachii and coracobrachialis. At the intertubecular groove, it gives a branch that travels superiorly in the sulcus to supply the glenohumeral joint.
The PCHA travels posteriorly alongside the axillary nerve through the quadrangular space. The PCHA then courses anteriorly around the surgical neck of the humerus, supplying the shoulder joint and the deltoid muscle and anastomosing with the ACHA and profunda brachii.