Brachhial pllexus injuries occur with anterior shoulder
dislocations because the brachial plexus is most tense when
the arm is abducted to 90 ° and fully extended. The brachial
plexus is a complex network of nerves arising from the
ventral rami of C5 through T1 (Figure 9). The brachial
plexus is commonly divided into supraclavicular and infraclavicular
components. The supraclavicular components
arise from the ventral rami posteriorly, continuing deep to
the clavicle but superficial to the first rib. The ventral rami of
C5 and C6 join to form the upper trunk. The middle trunk is
made up of the ventral rami of C7. The ventral rami of C8
and T1 form the lower trunk. Each of these trunks then
divides into anterior and posterior divisions. The three
posterior divisions join and form the posterior cord. The
anterior divisions of the upper and middle trunks form the lateral cord. The anterior division of the lower trunk
becomes the medial cord. Each of these cords divides into
terminal branches. The termilnal branches determine the
physical findings found with brachial plexus injuries. The
lateral root forms the median and musculocutaneous nerves.
The medial root contributes to the median nerve and forms
the ulnar nerve. The posterior cord divides into radial and
axillary nerves.