Traction
Traction occurs from severe movement and causes a pull or tension among the nerves. There are two types of traction: downward traction and upward traction. In downward traction there is tension of the arm which forces the angle of the neck and shoulder to become broader. This tension is forced and can cause lesions of the upper roots and trunk of the nerves of the brachial plexus. Motorcycle accidents and sports injuries usually cause this type of injury to brachial plexus. Upward traction also results in the broadening of the scapulo-humoral angle but this time the nerves of T1 and C8 are torn away. Humeral fractures and shoulder dislocations can also cause this type of injury with high energy injuries.Root avulsion or nerve rupture may occur during severe trauma, inappropriate surgical positioning, or inappropriate use of surgical retractors. There are two mechanisms for root avulsion injury: peripheral and central mechanism. In peripheral mechanism, traction is transmitted to the rootlet, however dura mater will be torn with the rootlet intact because the dura is less elastic when compared to the rootlet. Pseudomeningocele can be shown on cervical myelography. On the other hand, through central mechanism, the head and neck is pushed along with the spinal roots of the brachial plexus to the opposite site of the body, leading to direct nerve root injury but the dura sheath remains intact. In this case, anterior roots are more prone than posterior roots for avulsion, thus the C8 and T1 nerve roots are more prone to injury.
The most severe form of injury is nerve root avulsion, which usually accompanies high-velocity impacts that commonly occur during motor-vehicle collisions or bicycle accidents. Disabilities
Based on the location of the nerve damage, brachial plexus injuries can affect part of or the entire arm. For example, musculocutaneous nerve damage weakens elbow flexors, median nerve damage causes proximal forearm pain, and paralysis of the ulnar nerve causes weak grip and finger numbness. In some cases, these injuries can cause total and irreversible paralysis. In less severe cases, these injuries limit use of these limbs and cause pain.The cardinal signs of brachial plexus injury then, are weakness in the arm, diminished reflexes, and corresponding sensory deficits. Erbs palsy. "The position of the limb, under such conditions, is characteristic: the arm hangs by the side and is rotated medially; the forearm is extended and pronated. The arm cannot be raised from the side; all power of flexion of the elbow is lost, as is also supination of the forearm". In Klumpkes paralysis, a form of paralysis involving the muscles of the forearm and hand, a characteristic sign is the clawed hand, due to loss of function of the ulnar nerve and the intrinsic muscles of the hand it supplies. Causes
In most cases, the nerve roots are stretched or torn from their origin, since the meningeal covering of a nerve root is thinner than the sheath enclosing the nerve.