Thoracic Outlet Syndrome

Thoracic outlet syndrome (TOS) is a syndrome involving compression at the superior thoracic outlet wherein excess pressure placed on a neurovascular bundle passing between the anterior scalene and middle scalene muscles. It can affect one or more of the brachial plexus (nerves that pass into the arm from the neck), the subclavian artery, and - rarely - the vein, which does not normally pass through the scalene hiatus (blood vessels as they pass between the chest and upper extremity.

TOS may occur due to a positional cause - for example, by abnormal compression from the clavicle (collarbone) and shoulder girdle on arm movement. There are also several static forms, caused by abnormalities, enlargement, or spasm of the various muscles surrounding the arteries, veins, and/or brachial plexus, a fixation of a first rib, or a cervical rib. A Pancoast tumor (a rare form of lung cancer in the apex of the lung) can lead to thoracic outlet syndrome in the progressive stages of the disease. The most common causes of thoracic outlet syndrome include physical trauma from a car accident, repetitive injuries from a job such as frequent non-ergonomic use of a keyboard, sports-related activities, anatomical defects such as having an extra rib, and pregnancy.

Common orthopaedic tests used are the Adson's test, the Costoclavicular Manoeuvre, and the "Hands-Up" test or "EAST" test. Careful examination and X-ray are required to differentially diagnose between the positional and static aetiologies, first rib fixations, scalene muscle spasm, and a cervical rib or fibrous band.