Credit: ACA News February 2009 http://www.acatoday.org/content_css.cfm?CID=3256 By Angela Kargus The thoracic outlet is a small space between the collarbone (clavicle) and the first rib. Thoracic outlet syndrome (TOS) is a group of disorders that involve compression, injury, or irritation of the nerves, blood vessels, or veins in the thoracic outlet....