Introduction to Thoracic Outlet Syndrome

What is Thoracic Outlet Syndrome?

Thoracic outlet syndrome (TOS) is a complex disorder characterized by a constellation of signs and symptoms resulting from the compression of blood vessels and nerves (neurovascular bundle) in the thoracic outlet region where they exit the chest. The thoracic outlet is a space located between the thorax (rib cage) and the clavicle (collar bone) which contains major blood vessels (subclavian artery and vein) and nerves (brachial plexus). The thoracic outlet is the area through which nerves and blood vessels travel to and from the arm.

Thoracic outlet syndrome is considered a "syndrome" since it involves multiple systems, including:

• Neural complex
• Vascular structures
• Musculoskeletal system

Neural Complex

The nerves that travel through the thoracic outlet originate at the level of the cervical and/or thoracic spine (C5-C8 and T1). These nerves are bundled together into the brachial plexus. The brachial plexus passes through a notch in the bone at the base of the neck and then passes under the scalene muscles and continues under the collarbone and across the front of the shoulders. In the area of the axilla (arm pit) the brachial plexus divides into the three major nerves of the arm, ulnar, median, and radial nerves. Thoracic outlet syndrome involves the brachial plexus before it divides and typically affects the ulnar and radial nerves.

Vascular Structures

The blood vessels that travel through the thoracic outlet include:

• Subclavian artery which supplies oxygenated blood to the arm from the aorta
• Subclavian vein which returns the deoxygenated blood from the arm to the heart

Musculoskeletal System

The bones and muscles form the backdrop for proper passage and support for the nerves and blood vessels that traverse the upper body. The components involved in this process include:

• Proper bone alignment - the neck vertebrae, first rib and collarbone must be aligned properly to allow enough space for the brachial plexus and subclavian blood vessels to pass through the correct path without obstruction or interference.

• Proper muscle alignment - muscles of the upper body must be aligned in proper form, particularly the scalene muscles. The scalene muscles consist of three powerful muscles on each side of the neck that bend and rotate the neck, and assist in breathing by raising the first two ribs during inspiration (breathing in). The ideal posture which promotes the most appropriate muscle alignment is when the head sits directly atop the shoulders which we identify as erect posture.