What causes thoracic outlet syndrome?
Neurogenic TOS is most often the result of neck trauma such as a whiplash injury. Slipping and falling on floors or ice, or repetitive stress from working on assembly lines or keyboards are the next most common causes. The symptoms are due to scar tissue formation in neck muscles (called scalene muscles). Venous TOS is commonly due to strenuous use of the arm and shoulder. Its underlying cause is congenital narrowing of the space through which the major arm vein (subclavian vein) passes from the shoulder area into the heart. Arterial TOS is caused by a narrowing in the main artery to the arm (subclavian artery) which invariably is secondary to a congenital extra rib (cervical rib) which lies at the base of the neck, just above the highest rib in your chest, or it can be secondary to an abnormal first rib. Once the artery has been narrowed, one of two things will happen. The artery may enlarge, forming an aneurysm just beyond the narrowing, and a clot will form in the wall of the aneury
