fyi, I recently read the info below -- which seems to link nerve root irritation with muscle spasm of the scalenes, leading to TOS.

http://www.nismat.org/patients/injur...in-in-the-neck

What causes the neurovascular compression?

Compression occurs when the size and shape of the thoracic outlet is altered. The outlet can be altered by exercise, trauma, pregnancy, a congenital anomaly, an exostosis, postural weakness or changes.

Below is a list of the component syndromes which comprise thoracic outlet syndrome along with a brief description of each. Refer to the scheme for questions about the gross anatomy of the region.

Anterior scalene tightness
Compression of the interscalene space between the anterior and middle scalene muscles-probably from nerve root irritation, spondylosis or facet joint inflammation leading to muscle spasm.

Costoclavicular approximation
Compression in the space between the clavicle, the first rib and the muscular and ligamentous structures in the area-probably from postural deficiencies or carrying heavy objects.

Pectoralis minor tightness
Compression beneath the tendon of the pectoralis minor under the coracoid process-may result from repetitive movements of the arms above the head (shoulder elevation and hyperabduction).