Segmental muscle innervation as a basic anatomophysiological knowledge for diagnostic procedure of neuromuscular disorders and thus, a way for accurate EMG diagnosis of single root injury. Retrospective study in patients with radicular symptoms

Abstract

Background: An accurate identification of the injured nerve roots by EMG in patients with symptomatic
CSD requires that the examined muscles are innervated by a single nerve root. In the present retrospective
study, the authors address the question of whether such innervation of chosen muscles in the upper
extremity can be identified.

Methods: Scored EMG results of chosen muscles with the hypothesized innervation by C6, C7 or C8
nerve roots, collected from 42 patients, were compiled as single EMG variables and compared with
the respective MRI data, possibly responsible for injury of those roots, using Spearman’s rho (SRC)
analysis. Subsequently, each EMG variable was adopted as specific diagnostic method for single root
injury and tested for its specificity and then sensitivity in relation to the data of the highest ranked MRI,
used as a ‘gold standard method’

Results: SRC results showed positive rank correlation, with the highest p-values, between EMG and
the respective MRI variables, in 64 included extremities. Consequently, the assumed EMG-C6, -C7 and
-C8 methods showed a high specificity (97% - 100%) against the respective highest ranked MRI. The
relative sensitivity of the EMG methods calculated in this way were 38% for the C6-root, 87% for the
C7 and 50% for the C8.

Conclusions: The results corroborate the presumed innervation of the chosens muscles by single C6,
C7, or C8 nerve root, thus allowing the use of needle EMG examination of those muscles for accurate
identification of injured single nerve roots in patients with symptomatic CSD.