Background: Thoracic Outlet Syndrome (TOS) is a clinical entity that develops due to compression against the shoulder girdle. Symptoms usually develop from compression of the brachial plexus and the subclavian vessels between the clavicle and the first rib. Despite of the patients’ vague symptoms, the clinical presentation of TOS is very consistent. Thoracic Outlet Syndrome is more common in women and the usual age distribution ranges from the second to the third decade. This syndrome has been associated to traumatic etiologies such as whiplash injuries from motor vehicle collisions, prolonged periods of upper extremity abduction, or the use of vibrating tools. Multiple hypotheses have attempted to explain the variety of symptoms observed in patients with TOS. Cumulative trauma disorders and muscle imbalance patterns with nerve compressions are some of the most prevalent theories regarding the pathogenesis of this controversial syndrome. Mild to moderate cases of TOS may benefit from conservative treatment while surgical interventions are reserved for severe cases. We propose that an adventitial fibrous band over the first rib is the etiology of the TOS. The purpose of our study is to identify the fibrous band of the first rib and describe its anatomic relationship to nerve roots and brachial plexus.
Material and Methods: One hundred first thoracic ribs were dissected from 70 embalmed cadavers. Thirty six cadavers were female and 34 were male. The age range was from 15 to 75 years with its majority in the 5th decade (mean of 54.3 years old). Twenty seven patients were African American, twenty two were Caucasian, twelve were Hispanics and 9 were Asian. The dissections were performed for evaluating for the presence of a congenital fibrous band within the first rib.
Results: We performed 100 dissections on 70 embalmed cadavers, 60 cadavers having bilateral dissections. Twelve dissections involved the right first ribs and 28 left first ribs. The dissections demonstrated the presence of thirty five fibrous bands intrinsic to the first rib (35% incidence; 35/100). This band always originated from the concave surface of the first rib, lateral to the head of the rib (1.34 cm). Its insertion is lateral to the anterior scalene tubercle (0.59 cm). The width and length of the band were 0.27 cm and 3.45 cm, respectively. The band was found to be distinct to the scalene minimus muscle, but when both are present they fuse near its insertion. The scalene minimus muscle was found on 11 of the dissected first ribs (11% incidence; 11/100). The fibrous band consistently created a space through which the T1 nerve root passes. The interspace created by the band measured 0.60 cm.
Conclusion: Our dissections showed that this fibrous band always creates a space through which T1 nerve root passes. Contrary to previous reports, the T1 nerve root does not cross over this fibrous band. Since, costo-clavicular compression of the brachial plexus and the subclavian vessels seems to be main pathophysiologic mechanism responsible for this syndrome. It is possible that this intrinsic first rib band plays an important role in the TOS. We suggest that this fibrous band may be a potential site of nerve entrapment and causes symptoms related to the thoracic outlet syndrome. Knowledge of this band may change our clinical concept and surgical approach. We are presently evaluating this fibrous band by magnetic resonance imaging (MRI) in both cadaver and clinical settings.