Thoracic outlet syndrome(TOS) is a syndrome involving compression at the superior thoracic outlet involving compression of a neurovascular bundle passing between the anterior scalene and middle scalene. It can affect the brachial plexus (nerves that pass into the arms from the neck), and/or the subclavian artery or rarely the vein which does not normally pass through the scalene hiatus (blood vessels as they pass between the chest and upper extremity). Rarely a Pancoast tumour in the apex of the lung may be the cause. The compression may be positional (caused by movement of the clavicle and shoulder girdle on arm movement) or static (caused by abnormalities or enlargement or spasm of the various muscles surrounding the arteries, veins, and brachial plexus), a first rib fixation and a cervical rib...