Damage to the upper nerves that make up the brachial plexus tends to occur when your shoulder is forced down while your neck stretches up and away from the injured shoulder. The lower nerves are more likely to be injured when your arm is forced above your head.
These injuries can occur in several ways, including:
- During birth. In babies, the brachial plexus nerves in the shoulder are vulnerable during birth. Injury to the brachial plexus is fairly common in newborns, occurring in one to two births per 1,000. Larger babies in difficult vaginal deliveries are particularly prone to this injury, as are babies with high birth weight, breech presentation or prolonged labor. If an infant's shoulders get wedged within the birth canal, there is an increased risk of a brachial plexus palsy. Most often, the upper nerves are injured, a condition called Erb's palsy.
- Contact sports. Many football players experience burners or stingers, which can occur when the nerves in the brachial plexus get stretched beyond their limit during collisions with other players.
- Trauma. Several types of trauma — including motor vehicle accidents, motorcycle accidents, falls or bullet wounds — can result in brachial plexus injuries.
- Tumors and cancer treatments. Tumors can grow in or along the brachial plexus, or put pressure on the brachial plexus or spread to the nerves. Radiation treatments to the chest may cause damage to the brachial plexus.