Scapular instability associated with brachial plexus irritation: a proposed causative relationship with treatment implications.

Brachial plexus irritation and other compression neuropathies can be diverse in their presentations and can cause a myriad of signs and symptoms. The purpose of this paper is to review the pertinent anatomy, kinesiology, and neurophysiology and to outline one possible cascade of events that may contribute to more diffuse upper extremity symptoms. Scapular instability and local myofascial trigger points resulting in possible secondary muscle imbalances are described. Their possible relationship to brachial plexus irritation in addition to the implications of the irritation are also discussed. The author postulates that proximal nerve irritation in the region of the thoracic outlet and shoulder may help to account for diffuse or unrelieved symptoms following conventional treatment of distal extremity problems in patients with occupational or cumulative trauma disorders. This paper outlines specific examination procedures for the therapist, which include upper limb tension testing, extensibility testing of the pectoralis minor, and gross manual muscle testing of the lower trapezius.