Brachial plexus palsy: Paralysis of the arm due to an injury to the brachial plexus. The brachial plexus is a network of spinal nerves that originates in the back of the neck, extends through the axilla (armpit), and gives rise to nerves to the upper limb (arm). The brachial plexus is formed by the union of portions of the fifth through eighth cervical nerves and the first thoracic nerve, all of which come from the spinal cord.
Brachial plexus palsy is subdivided into upper and lower, depending on which trunk of the plexus is injured. Upper brachial plexus paralysis is called Erb palsy while lower brachial plexus paralysis is called Klumpke palsy. There can also be total brachial plexus palsy.
Brachial plexus injury is common in childbirth when the shoulder girdle is stretched.