The middle scalene muscle and its contribution to the thoracic outlet syndrome.

The predisposing anatomic alterations or features of thoracic outlet syndrome have been tallied to better define this difficult and inchoate issue. In the last 34 supraclavicular operations involving 33 patients (for a total operative experience of 128 procedures), we have found the anterior insertion of the middle scalene muscle to be present in 48 percent of our patients. This insertion, forward on the first rib, closes an already small interscalene triangle, so that the posteriorly placed brachial plexus is entrapped or irritated by the anterior edge of this muscle, which may be very sharp and firm. In addition, 10 percent of our patients had a middle scalene band intimately associated with the middle scalene muscle, often-times inseparable, for a 58 percent incidence of middle scalene involvement in the thoracic outlet syndrome. With data such as those presented herein, a more simplified operation than the heretofore popular all-out attack on the first rib may well be in the offering.