Divisions of the Brachial Plexus

divisiones anteriores et posteriores plexus brachialis

Behind the clavicle, each of the three trunks splits into an anterior and a posterior division, giving six divisions in all. The anterior divisions carry fibres for the front (flexor) compartments of the limb and the posterior divisions carry fibres for the back (extensor) compartments. No named nerves arise from the divisions themselves.

Anatomical Data

Course & Distribution

Origin	Each trunk divides into one anterior and one posterior division
Course	Lie behind the middle third of the clavicle and the subclavius as the plexus passes from the neck into the axilla, then regroup to form the lateral, medial and posterior cords
Motor	Anterior divisions: flexor muscles of the arm, forearm and hand Posterior divisions: extensor muscles of the arm and forearm, deltoid, latissimus dorsi, subscapularis and teres major
Sensory	Anterior divisions: front of the limb and palm Posterior divisions: back of the arm, forearm and dorsum of the hand

Clinical Relevance

Clinical Notes

The divisions regroup into cords: the anterior divisions of the superior and middle trunks form the lateral cord, the anterior division of the inferior trunk forms the medial cord, and all three posterior divisions form the posterior cord. This retroclavicular part of the plexus can be injured by displaced clavicle fractures, excess callus after fracture healing, or compression between the clavicle and first rib. The flexor and extensor split explains why posterior cord and radial lesions affect only extension.

Pathology

Common Injuries & Conditions

Retroclavicular Plexus Injury

Displaced or healing clavicle fractures can compress or stretch the divisions behind the clavicle, causing a mixed pattern of weakness and numbness. Symptoms often improve after fracture fixation or removal of excess callus.

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