Anatomy of the Brachial Plexus

Brachial Plexus, Nerves, Roots, Trunk

The Brachial Plexus is a complex anatomical nerve structure connecting the spinal cord at the cervical level with the nerves supplying cutaneous and muscular innervation of the entire upper limb.

The plexus is formed by the ventral rami (roots) of the lower 4 cervical nerves (C5 C6 C7 C8) and the first thoracic nerve (T1).
The roots connect themselves to form the trunks: C5 and C6 rooots form the upper trunk, C7 forms the middle trunk while C8 and T1 roots form the lower trunk. Afterward each trunk divides into two branches an anterior and a posterior one, which give origin to the cords (lateral, posterior and medial) that will distally contribute to form the nerves destinated to the arm. The name anterior, posterior or medial define the relationship of the cords with the axillary artery.

It is interesting to situate topographically the different parts of the plexus in order to better understand the mechanism of lesions and to facilitate the clinical examination and the diagnosis of the level of lesion.
Actually the roots occupy the interscalenic space that means very close to the cervical spine. The trunks are situated in the supraclavicular region while their divisions forming the cords lie behind the clavicle; the cord (lateral, posterior and middle) occupy the infraclavicular region while the division into the distal nerves is completed in the axillary region.
There may be anatomical variation in the plexus mainly at the level of C7 division and in the formation of cords and distal nerves that surgeon must know since it can influence the diagnosis of the level of lesion and consequently the strategy of repair.