Causes

TOS results from compression of nerves or vessels in the thoracic outlet. Causes of such compression can include:

Trauma – Traumatic events can injure the bones or soft tissues around the thoracic outlet. Most people with TOS have some type of trauma, such as a car accident or work-related injury, before they experience symptoms.

Anatomical defects – An abnormality present since birth, such as an extra (cervical) rib or an abnormally tight fibrous band connecting the spine to a rib, can compress the thoracic outlet.

Poor posture – Sagging your shoulders or holding your head forward can place extra pressure on nerves and blood vessels in the thoracic outlet.

Repetitive activities – Repeating an arm movement can wear on body tissues and lead to TOS. Overhead actions are especially likely to produce symptoms, perhaps because raising the arms presses the collarbone downward, narrowing the thoracic outlet. Examples of activities that may cause or worsen TOS symptoms include stocking high shelves, repeatedly lifting items overhead, and athletic pursuits such as swimming, baseball pitching, tennis or weightlifting.

Other causes – Weight gain (such as from pregnancy or obesity), overdeveloped neck muscles (such as from weightlifting and some contact sports), or keeping your arms in the same position for prolonged periods (such as when working at a computer) can place extra pressure on nerves and blood vessels. Diseases that affect nerve function, such as hypothyroidism and diabetes, may predispose people to neurogenic TOS symptoms.