Brachial plexus palsy, also known as Erb's palsy, is a paralysis or weakness of the arm caused by an injury to one or more nerves that control and supply the muscles of the shoulder and upper extremities (upper brachial plexus). It is more commonly seen in newborns (neonates) and is often the result of a difficult delivery. When it occurs in adults, the cause typically is an injury that has caused stretching, tearing or other trauma to the brachial plexus network. The brachial plexus is the network of nerves that conducts signals from the spine to the shoulder, arm, and hand.
There are four types of brachial plexus injury, avulsion, the most severe type, in which the nerve is ripped from the spine, rupture, in which the nerve is torn but not at the point at which it is attached to the spine; neuroma, in which the nerve is torn and has tried to heal but scar tissue has grown around the site; and neuropraxia (stretch), the most common form of injury, in which the nerve has been damaged but not torn.