Superior Trunk of the Brachial Plexus

Description

Arising from the C5 and C6 ventral rami at the lateral margin of the intervertebral foramina, the superior trunk of the brachial plexus courses inferolaterally across the posterior triangle of the neck toward the root of the neck, framed superiorly by the cervical spine and laterally by the clavicle and scapular girdle. Its bifurcation into anterior and posterior divisions appears just proximal to the clavicle, where the plexus transitions toward the supraclavicular and infraclavicular regions. Surrounding osseous landmarks include the skull base and mandible superiorly, cervical vertebrae medially, and the first ribs and upper thoracic cage inferiorly. Blue vascular elements track near the plexus, consistent with the close relationship of trunks and divisions to the subclavian and proximal axillary vessels. Clear separation of the superior trunk into anterior and posterior divisions matters because it previews the later formation of the lateral and posterior cords, a point that often confuses learners when cords are introduced without a strong supraclavicular map. Clinically, this segment is implicated in upper brachial plexus traction injuries (Erb-Duchenne palsy), where C5 to C6 involvement produces weakness in shoulder abduction and lateral rotation with impaired elbow flexion. It is also a frequent target for ultrasound-guided supraclavicular brachial plexus block, where anesthetic spread around the compact cluster of trunks risks diaphragmatic paresis if the phrenic nerve is affected and risks pneumothorax if the needle drifts too inferiorly. Small distances matter here. Use this artwork for gross anatomy and regional anatomy teaching of the neck and shoulder, for anesthesia and pain publications discussing supraclavicular approaches, and for clinical education on brachial plexus injury patterns that localize to the superior trunk and its divisions. Anatomical accuracy verified by SciePro's Medical Advisory Board.