Mechanisms of brachial plexus lesions.

The main causes of brachial plexus palsies are traction, due to extreme movements, and heavy impact. In downward traction of the arm and forcible widening of the shoulder-neck angle the lesion will occur in the upper roots and trunk. Forcible upward traction will cause avulsion of T1 and C8. The most violent trauma will result in a lesion at all levels. Rupture of the cords and/or individual infraclavicular nerves will be produced by traction and/or forcible widening of the scapulohumeral angle. Vascular structures are subjected to the same mechanism and injuries of these structures give information about the site and severity of nerve lesions; fractures of the skull, cervical spine, clavicle, first rib or arm yield further data on the mechanism of trauma that has produced the brachial plexus palsy. Heavy impact or crush lesions are caused by direct trauma to the (supra)clavicular region and are nearly always associated with fracture of the clavicle.