Anatomical relationship of Roos' type 3 band and the T1 nerve root.

Background: The most common clinical presentation of thoracic outlet syndrome stems from compression of the lower trunk of the brachial plexus or ulnar nerve. A plethora of anatomical variations have been implicated in the cause of thoracic outlet syndrome. Roos' identification and classification of scalene muscle and fibrous bands have added an additional dimension to understanding its cause and subsequent treatment. Understanding the anatomy and relationship of this band with the lower trunk of the brachial plexus is of paramount importance.

Methods: As part of the authors' long-term study of the type 3 band in relation to the brachial plexus, 70 embalmed cadavers were dissected to yield 100 first thoracic ribs. Fibrous bands, when present, were studied in relation to the brachial plexus.

Results: A fibrous band consistent with Roos' type 3 was identified and found to occur in 35 percent of first ribs and 41 percent of cadavers. The mean size was 3.45 × 0.27 cm. Origins and insertions are described. Contrary to Roos' own description, however, the authors observed that Roos' type 3 band was anterior to the T1 nerve root, creating a tunnel through which the T1 nerve root must pass before joining the C8 nerve root.

Conclusions: The authors believe that the type 3 band, when present, can create a tunnel that compresses the T1 nerve root against the first rib, potentially predisposing susceptible individuals to thoracic outlet syndrome. Clinical studies are needed to determine whether correlations between type 3 bands and thoracic outlet syndrome exist.