Bilaterally anomalous formation and distribution of posterior cord of brachial plexus.

ABSTRACT

Posterior cord (PC) is formed by the union of posterior divisions of upper, middle and lower trunks. During routine dissection variations in the formation and distribution of PC and its branches were observed on both the sides. These variations were i) prefixed brachial plexus on left side ii) PC on both the sides was formed by the union of posterior divisions of only the upper (C5, 6) and middle (C7) trunks while the posterior division of lower (C8, T1) trunk joined the radial nerve directly and also gave contribution by two roots to left thoracodorsal nerve iii) length of PC varied on both the sides; on right side it was 4cm while on left side it was 1.5cm long. iv) upper subscapular nerve on right side arose from PC far proximal to other branches and on its course communicated with lower subscapular nerve before distributing to subscapularis while on left side it arose from posterior division of the upper trunk (C5, 6) only. v) on left side nerve to teres minor arose directly from axillary nerve trunk instead of arising from its posterior branch. The axillary nerve on both the sides divided into terminal branches before entering the quadrangular space of arm instead after traversing the quadrangular space. vi) the branches of radial nerve, which normally arise in the radial groove, arose in the axilla on both the sides. So in cases of trauma or injury of arm some of these branches may be spared.