Posterior Division of Superior Trunk of Brachial Plexus (Right)

Origin

The origin of the posterior division of the superior trunk is from the superior trunk itself. This occurs when the trunk bifurcates into anterior and posterior divisions. It carries fibers from the C5 and C6 spinal segments.

Course

The posterior division of the superior trunk forms on the border of the posterior triangle and the axilla, roughly posterior to the mid-clavicle. It runs inferolaterally, assuming a position posterior to the first segment of the axillary artery.

The divisions of the brachial plexus run within the prevertebral fascia or its inferior extension, the axillary sheath.

Branches

The posterior division of the superior trunk itself has no branches as it generally does not give rise to any nerves. However, it merges with the posterior divisions of the middle and inferior trunks to form the posterior cord. The contribution of the posterior division of the superior trunk to this cord gives rise to the following nerves:

—upper subscapular nerve;

—thoracodorsal nerve;

—lower subscapular nerve;

—axillary nerve;

—radial nerve.

Supplied Structures

The posterior division of the superior trunk supplies the structures innervated by the posterior cord. This includes posterior and lateral surfaces of the arm, forearm, and hand (sensory), and the muscles of the posterior axilla and posterior compartment of the arm and forearm (motor). Broken down by nerve, the structures supplied by the posterior division of the superior trunk are:

—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.