The three main mechanisms of a<unk> include receiving direct blows, extension, and compression of the brachial plexus, with most of the brachial plexus injuries being an extension-compression mechanism. A<unk> is an injury that is caused by restriction of the nerve supply to the upper extremity via the brachial plexus. The brachial plexus is formed by the anterior rami of the nerves at the 5th cervical level of the spinal cord all the way to the nerves at the 1st thoracic level of the spinal cord. The brachial plexus innervates the upper extremity as well as some muscles in the neck and shoulder. Damage to the brachial plexus can occur when the nerves are stretched too far from the head and neck; specifically the upper trunk of the plexus –nerve roots at the 5th and 6th cervical level –are primarily affected. The upper trunk provides part of the nerve to supply to the upper extremity via the Musculocutaneous, Axillary, Radial and Median nerves. It is for this reason that<unk>  do not affect both arms simultaneously, however it is possible for both arms to accrue injuries. Repeated nerve trauma can cause recurring<unk> , chronic pain, and muscle weakness, while recovery can take weeks to months in severe cases. Since<unk>  are a nerve injury, a<unk> can fall into two different categories of peripheral nerve injury with physiological differences. Grade I is neurapraxia, which involves focal damage of the myelin fibers around the axon, with the axon and the connective tissue sheath remaining intact. The disruption of nerve function involves demyelination. Axonal integrity is preserved, and remyelination occurs within days or weeks. Grade II is categorized by axonotmesis which is the most severe case of nerve injury in the context of<unk>  and involves the injury of the axon. Grade III is classified as neurotmesis where there is a complete disruption of the axon, where it is unlikely of recovery. If this is to happen it is not considered a<unk>  and usually is a high-energy injury to the shoulder-girdle.
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