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Thoracic Outlet Syndrome

Thoracic outlet syndrome 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 (nerve) complexes
  • 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.

Anatomy of the Thoracic Outlet


There are actually three spaces where compression can occur causing the symptoms of thoracic outlet syndrome , including:

  • The thoracic outlet (also called the scalene triangle) - is located at the base of the neck above the first rib and behind the clavicle. This space lies closest to the neck. The boundaries of the thoracic outlet consist of:
    • anterior scalene muscle which forms the front of the thoracic outlet
    • middle scalene muscle which forms the back of the thoracic outlet
    • first rib which forms the bottom of the thoracic outlet.  

The subclavian artery and the brachial plexus are located between the first rib and the scalene muscle while the subclavian vein sits outside the scalene muscle.

  • Costoclavicular space - this space is located adjacent to the scalene triangle and lies between the following structures:
    • clavicle
    • first rib
    • costoclavicular ligament
    • edge of the middle scalene muscle 

The subclavian artery, vein, and brachial plexus all pass through the costoclavicular space.

  • Subcoracoid space which lies adjacent to the costoclavicular space and is closest to the arm. The location of this space is:
    • under the pectoralis muscle
    • under the coracoid process
    • in front of the ribs
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