Thoracic outlet syndrome, or TOS, causes compression of neurovascular tunnels, which contain major nerves, arteries and veins to the arm. Actually, it’s more than just one outlet. In fact there are quite a few.
It can start as soon the nerves exit the neck and upper back. Degenerative conditions of the spine can affect the nerves and some blood vessels at this point. It can also occur where the nerves and blood vessels pass under the scalene muscles of the neck and become compressed. The third tunnel is underneath the collar bone called the clavical.
The picture below depicts the fourth tunnel which is located beneath the pectoralis minor muscle (partially cut away).
In addition to the thoracic outlets, there are two other neurovascular tunnels in the arm that are sometimes coupled with TOS. One is under the brachioradialis muscle of the forearm. The sixth and last tunnel is under and between the wrist bones. Epicondylitis or tennis elbow involves the brachioradialis compartment. Carpal tunnel syndrome involves the wrist compartment.
TOS can be caused by anything that disturbs, distorts or deforms the bone and soft tissue tunnels of the thoracic outlets. One of the major distortions of the spine to affect the thoracic outlets is scoliosis.