Posterior Cord of Brachial Plexus

Origin

The origin of the posterior cord is from the merger of the posterior divisions of the superior, middle, and inferior trunks. It carries fibers from the C5 through T1 spinal segments.

Course

From its origin roughly lateral to the first rib, the posterior cord runs inferolaterally through the axilla. It begins and remains posterior to the axillary artery.

The posterior cord gives off three branches posterior to the second segment of the axillary artery. It then continues down along the axillary artery until it terminates in the lower axilla, medial to the third segment of the axillary artery.

The cords of the brachial plexus run within the axillary sheath which is an inferior extension of the prevertebral fascia.

Branches

The posterior cord gives rise to the following nerves:

—upper subscapular nerve;

—thoracodorsal nerve;

—lower subscapular nerve;

—axillary nerve;

—radial nerve.

Supplied Structures

The posterior cord conveys both sensory and motor innervation. Sensory innervation includes posterior and lateral surfaces of the arm forearm, and hand. Motor innervation includes muscles of the posterior axilla and posterior compartment of the arm and forearm. Broken down by nerve, the structures supplied by the posterior cord:

—upper subscapular nerve supplies motor innervation of the subscapularis muscle;

—thoracodorsal nerve supplies motor innervation of the latissimus dorsi muscle;

—lower subscapular nerve supplies motor innervation of the subscapularis muscle;

—axillary nerve supplies sensory to skin of the lateral arm and motor innervation of the deltoid and teres minor muscles;

—radial nerve supplies sensory to skin of the posterolateral arm, posterior forearm, and posterolateral hand and motor innervation to the muscles of the posterior compartment of the arm and forearm.