Determining C5, C6 and C7 myotomes through comparative analyses of clinical, MRI and EMG findings in cervical radiculopathy

Abstract

Objective: There are many myotome charts in the literature, but few studies have presented actual data to support their identification. We aimed to determine C5/C6/C7 myotomes based on clinical and EMG data of patients with cervical spondylotic radiculopathy (CSR) having a single-root lesion confirmed by MRI.

Methods: Medical Research Council (MRC) scores and EMG findings were retrospectively reviewed for patients enrolled from our EMG database.

Results: Enrolled were 25 patients (10 C5, 6 C6, and 9 C7 CSR). In C5 CSR, weakness or denervation potentials in EMG, or both, were observed in the deltoid (Del) and infraspinatus (Isp) muscles for all patients, and in the biceps brachii (BB) and brachioradialis (BR) muscles for 9/10 and 8/9 patients, respectively. In C6 CSR, weakness of the wrist extensor and/or denervation of the extensor carpi radialis longus (ECRL)/extensor carpi radialis brevis (ECRB), and those of the pronator teres (PT) were observed for all patients. Weakness was not observed for any other muscle in C6 CSR. Denervation potentials of ECRL were found in 5/8 and 3/5 patients with C5 and C6 CSR, respectively, whereas those of ECRB were found in 1/5, 6/6, and 2/5 patients with C5, C6 and C7 CSR, respectively. In C7 CSR, weakness/denervation of the triceps brachii (TB) and denervation potentials of the flexor carpi radialis (FCR) were observed for all patients. Denervation potentials in PT and weakness/denervation of the extensor digitorum (ED) were observed in 2/9 and 4/9 patients, respectively.

Conclusion: Suggested dominant myotomes are: C5 for the Del, Isp, BB, and BR, C5/6 for the ECRL, C6 > C7 for the ECRB and PT, and C7 for the TB and FCR.

Significance: The current study identified dominant myotomes that differ from the existing literature.

Keywords: Brachioradialis; Cervical spondylotic radiculopathy; Extensor carpi radialis brevis; Extensor carpi radialis longus; Myotome; Pronator teres.

Fig. 1

MRC scores and EMG grades for evaluated muscles of individual patients. MRC score: 5; 4; ≤3; no data. Grades for spontaneous activities (S): 0, none; 1, few; 2 moderate (observed following about half of insertions) and 3 (observed following almost every insertion); no data. Grades for voluntary activities (V): 0, normal; 1, reduced; 2 discrete and 3 single oscillation; no data. Del, deltoid; Isp, infraspinatus; BB, biceps brachii; BR, brachioradialis; WE, wrist extensors; ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis; PT, pronator teres; TB, triceps brachii; WF, wrist flexors; FCR, flexor carpi radialis; FCU, flexor carpi ulnaris; ED, extensor digitorum; PSM, paraspinal muscles; S, spontaneous activities; V, voluntary activities; MRC, Medical Research Council; CSR, cervical spondylotic radiculopathy.

Fig. 2

Typical myotome charts from the literature, together with our identification. Authors presenting raw data as the basis for their identification are written in bold letters, together with the number of patients included in each study (n). Note that this is the total number of patients and the number of patients having lesion of a specific root or receiving stimulation of a specific root is smaller. Dominant innervation; lesser contributions (studies with raw data). Dominant innervation; lesser contributions (studies without raw data). *For the present authors, results of Chiba et al. (2015) and this study were combined, and were graded semi-quantitatively as follows according to the percentage of patients showing abnormal results, except when we had too few data. In the latter situation, the grade was sometimes modified by other experiences of the authors or with reference to past studies. 60% or more; between 20 and 60%; 20% or less. ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis.