Superior Trunk of the Brachial Plexus

Description

Arising from the anterior rami of C5 and C6, the superior trunk of the brachial plexus is shown in the lower lateral neck as it courses inferiorly toward the axilla and divides into anterior and posterior divisions. The anterior division continues anteroinferiorly to join the lateral cord, positioned lateral to the axillary artery and deep to pectoralis minor, while the posterior division contributes to the posterior cord posterior to the vessel. Surrounding landmarks in the axillary region include pectoralis major anteriorly, latissimus dorsi and teres major forming the posterior axillary fold, serratus anterior against the thoracic wall medially, and the proximal humerus laterally. Relationships matter here. Clinically, the superior trunk is the segment most often affected in Erb-Duchenne palsy from traction between the head and shoulder, producing weakness of deltoid, supraspinatus, infraspinatus, and elbow flexors via downstream involvement of the suprascapular, axillary, and musculocutaneous pathways. Its proximity to the clavicle and first rib also makes it vulnerable in thoracic outlet syndrome and during supraclavicular approaches, where distinguishing trunks, divisions, and cords relative to the subclavian and axillary vessels guides safe dissection. For regional anesthesia, this anatomy underpins supraclavicular and interscalene brachial plexus blocks, and explains why a block centered at C5 to C6 can spare the ulnar distribution. Use this illustration for upper limb anatomy teaching on brachial plexus organization (roots to trunks to divisions to cords), for surgical atlas figures on axillary exposure and neurolysis, or for anesthesia education on block target selection and expected sensory-motor patterns. It also fits clinical education materials on obstetric brachial plexus injury and thoracic outlet evaluation. Anatomical accuracy verified by SciePro's Medical Advisory Board.