Thoracic Outlet Syndrome (TOS) occurs when the nerves and vascular structures from the neck are compressed as they run through the shoulder into the upper arm. Many times, there may also be compression in the spine or further down the shoulder, elbow, arm or hand. Symptoms may include numbness, tingling, weakness, pain or blanching of any of the fingers.
The thoracic outlet is the space between your clavicle (collarbone) and your first rib. If the shoulder muscles in your chest are not strong enough to hold the clavicle in place, it can slip down and forward, putting pressure on the nerves and blood vessels that lie under it. Additionally, if certain muscles in the neck or chest are tight they can also compress the nerves going down the arm. TOS can result from injury, disease, or a congenital problem, such as an abnormal first rib. Poor posture can aggravate the condition.