Thoracic Outlet Syndrome, aka TOS, is a rare condition that involves pain in the neck and shoulder, numbness and tingling of the fingers, and a weak grip. The thoracic outlet is the area between the rib cage and collar bone. The cause of TOS can be due to several factors and depending on which anatomical structures are compressed: arteries, veins, or nerves. Compression can be of different magnitude in each of these structures. Therefore symptoms can be protean.