Superior Trunk of the Brachial Plexus, Anterior View

Description

Emerging between the anterior and middle scalene muscles, the C5 and C6 roots unite to form the superior trunk of the brachial plexus just superior to the clavicle, then course laterally toward the supraclavicular fossa. From an anterior perspective, the clavicles, manubrium, and upper ribs frame the plexus as it passes posterior to the sternocleidomastoid and toward the shoulder girdle, with the acromioclavicular region and proximal humerus partially included for orientation. Expected branch points are suggested at the trunk level, where anterior and posterior divisions form deep to the clavicle before reorganizing into cords around the axillary artery in the infraclavicular space. Small. But high stakes anatomy. Clinically, the superior trunk is the segment most often implicated in traction injuries after lateral neck flexion, classically producing an upper brachial plexopathy (Erb-Duchenne pattern) with weakness of shoulder abduction and external rotation and diminished biceps reflex. This anterior, supraclavicular relationship also matters for regional anesthesia: during a supraclavicular brachial plexus block, the plexus sits clustered lateral to the subclavian artery and superior to the first rib, a setup that explains both the speed of onset and the risk of pneumothorax if needle trajectory is misjudged. Teachers can drop this plate into gross anatomy labs to anchor surface anatomy of the posterior triangle, or into neuroanatomy and peripheral nerve modules when students need a clean map from roots to divisions before learning cords and terminal branches. It also fits orthopedic and trauma publications discussing upper plexus lesions, clavicle fractures, and supraclavicular surgical approaches to the thoracic outlet. Anatomical accuracy verified by SciePro's Medical Advisory Board.