Applied anatomy of the different mechanism that the brachial plexus are injuried in newborn and adult cases

Objective In order to identify the mechanism that the C_7 nerve root is more prone to avulsion in obstetric brachial plexus palsy (OBPP) comparing to that in adult brachial plexus injury, the anatomical features of brachial plexus nerve roots were investigated. Methods 1.6 newborn (12 sides) and 6 adult (12 sides) cadavers were dissected to observe the intravertebral and extravertebral morphological features of the C_5-T_1 nerve roots, which form the brachial plexus. The following data were recorded: the cranial angle of nerve roots with cords, the cranial angle of the anterior rami with cords, the length of the ventral root emerging zone, the length of the ventral roots, and the number of ventral rootlets. 2. In 6 fresh newborn cadavers, the C_5-T_1 nerve roots were histologically analyzed using hematoxylin eosin and Mallory trichrome staining to observe the connection between nerve roots and their surrounding tissue. Results 1. In newborns, the nerve roots emerged at a relatively more horizontal angle when compared with adults. Therefore, the cranial angle of C_7 nerve roots with cords in newborns were smaller than that of their anterior rami, whereas the trend was reverse in adults. 2. In newborns, the primary protective attachment of C_5-C_7 nerve roots was the transverse-radicular ligaments, which are composed of collagen fibers. The collagen composition of this ligament around C_7 nerve roots, however, was smaller than that of the ligament around C_5 and C_6 nerve roots. The difference was statistically significant (P0.05). Furthermore, the transverse-radicular ligaments of the C_5 and C_6 nerve roots were reinforced by Sharpey fibers at its insertion to the transverse process. Sharpey fibers were hardly seen at the ligament around the C_7 nerve root. Conclusion The higher incidence of C_7 avulsion injury in OBPP may be attributed to the gross anatomic features and relatively weak transverse-radicular ligaments in newborns.