“…The lesion is principally thought to occur at either the upper trunk 1,8,15 or division (A. Dossett et al, unpublished data, 1995) levels of the brachial plexus, or at the root level. 11,12,14,16 Three chief mechanisms of injury have been proposed 15 : nerve root compression in the neural foramen (that is, extension-compression, or "root," injuries), brachial plexus stretch (that is, traction, or plexus, injuries), and a direct blow to the plexus.…”