Thoracic outlet syndrome (TOS) is a group of disorders that occur when there is compression of the blood vessels or nerves in the passageway from the neck to the armpit (between the collarbone and the first rib).

There are three main types of TOS. The neurogenic (most common) type causes pain and weakness in the neck, and occasionally loss of muscle at the base of the thumb. The venous type results in swelling, pain, and possibly bluish colouration of the arm. The arterial type causes pain, coldness and paleness of the arm.

The cause of TOS may be due to trauma (like an accident or whiplash), repetitive arm movements or injuries (often sport-related strain), tumours, pregnancy, or anatomical variations (such as an extra rib). However, other conditions can produce similar symptoms (like a rotator cuff tear, cervical disc disorders, fibromyalgia, multiple sclerosis, and complex regional pain syndrome).

Exercises to strengthen the chest muscles and improve posture are very beneficial.

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