BPI is most commonly found in young healthy adults, from ages 14 to 63 years old, with 50% of patients between 19 and 34 years old. 89% of BPI patients are male. The rate of brachial plexus injury has been increasing. Children
OBPP, also known as obstetrical brachial plexus palsy, occurs primarily in young children at a rate of 0.38 to 1.56 per 1000 live births depending on the type of care and the average birth weight of infants in different regions of the world. For example, a study in the United States showed and incidence of OBPP of about 1.51 cases per 1000 live births, in a Canadian study, the incidence was between 0.5 and 3 injuries per 1000 live births, a Dutch study reported an incidence of 4.6 per 1000 live births. The risk of BPI at birth is highest for infants weighing more than 4.5 kg at birth born to diabetic women. Type of delivery also affects the risk of BPI. Brachial plexus injury risks for newborns are increased with gained birth weight, birth delivery where a vacuum is assisted, and not being able to handle glucose. Traumatic injuries
BPI has shown to occur in 44% to 70% of traumatic injuries, such as motorcycle accidents, sporting activities, or  workplace accidents. With 22% being motorcycle injuries and about 4.2% having plexus damage.
The epineurium of the nerve is contiguous with the dura mater, providing extra support to the nerve.Brachial plexus lesions typically result from excessive stretching; from rupture injury where the nerve is torn but not at the spinal cord; or from avulsion injuries, where the nerve is torn from its attachment at the spinal cord. A bony fragment, pseudoaneurysm, hematoma, or callus formation of fractured clavicle can also put pressure on the injured nerve, disrupting innervation of the muscles. A trauma directly on the shoulder and neck region can crush the brachial plexus between the clavicle and the first rib.Although injuries can occur at any time, many brachial plexus injuries happen during birth: the babys shoulders may become impacted during the birth process causing the brachial plexus nerves to stretch or tear. Obstetric injuries may occur from mechanical injury involving shoulder dystocia during difficult childbirth, the most common of which result from injurious stretching of the childs brachial plexus during birth, most often during vaginal birth, but occasionally Caesarean section. The excessive stretch results in incomplete sensory and/or motor function of the injured nerve.Injuries to the brachial plexus result from excessive stretching or tearing of the C5-T1 nerve fibers. These injuries can be located in front of or behind the clavicle, nerve disruptions, or root avulsions from the spinal cord. These injuries are diagnosed based on clinical exams, axon reflex testing, and electrophysiological testing. Brachial plexus injuries require quick treatment in order for the patient to make a full functional recovery (Tung, 2003).