Muscle-Nerve Root Correlation for EMG

Abstract & Commentary

Source: Tsao BE, et al. Comparison of surgical and electrodiagnostic findings in single root lumbosacral radiculopathies. Muscle Nerve. 2003;27:60-64.

Retrospective review of needle EMG findings on 45 patients studied during a 20-year period, with surgically verified compression of a single lumbosacral nerve root, was undertaken to determine the accuracy of traditional myotomal charts used to localize nerve root involvement. Only patients with preoperative neuroimaging were included. Patients with underlying polyneuropathy, previous surgery, surgical evidence of polyradiculopathy, or spinal stenosis were excluded. Muscles were classified as abnormal only if they demonstrated sustained fibrillation potentials on EMG. Muscles with polyphasic motor unit potentials without fibrillation potentials were not included (see Table 1).

Table 1

L2 (n = 1)   L3 (n = 1) L4 (n = 5) L5 (n = 26) S1 (n = 12)
AL AL AL (5) PL (16/16) BFLH (5/5)
iliacus iliacus iliacus (3/5) TFL (4/4) LG (10/11)
VL VM VL (4/5) TP (23/25) BFSH (8/9)
upper LPS upper LPS RF (3/3) EDB (20/24) MG (10/12)
VM(1/1) TA (20/26) ADQ (5/7)
    LPS(4/5)   EHL (8/11) GM (7/11)
LPS (12/26)  LSPS (3/12)
ADQ = abductor digiti quinti; AL = adductor longus; BFLH = biceps femoris long head; BFSH = biceps femoris short head; EHL = extensor hallucis longus; GM = gluteus maximus; LG = lateral gastrocnemius; LPS = lumbar paraspinal muscles; LSPS = lumbosacral paraspinal muscles; MG = medial gastrocnemius; PL = peroneus longus; RF = rectus femoris; TA = tibialis anterior; TFL = tensor fascia lata; TP = tibialis posterior; VL = vastus lateralis; VM = vastus medialis

Interestingly, L5 radiculopathy demonstrated normal biceps femoris short head in 13/13 examined, and S1 radiculopathy revealed normal semitendinosus and extensor digitorum brevis in all examined. Tibialis posterior is predominantly L5 innervated and was positive in only 2/11 with S1 radiculopathy. Medial and lateral gastrocnemii are predominantly S1 muscles, being positive in only 1/24 and 2/16, respectively, with L5 radiculopathy. Paraspinals were often unhelpful in L5 and S1 radiculopathy (12/26 and 3/12 positive, respectively) but were positive in the few with L2, 3, or 4 disease. Although the numbers are relatively small, pattern recognition allows many lumbosacral radiculopathies to be localized to a single level electrodiagnostically.


Cervical radiculopathy was similarly examined among 50 surgically proven single-root lesions.1 Patients with multiple radiculopathies, myelopathy, or previous surgery were excluded. Muscles were considered abnormal only if fibrillation potentials were documented in at least 3 sites in any given muscle, and EMG was performed a mean of 3.5 months after symptom onset in 46 patients in whom onset could be clearly defined (see Table 2).

Table 2

C5 (n = 7) C6 (n = 9) C7 (n = 28) C8 (n = 6)
IS (5/6) PT (7/9)  PT (17/28)  EIP (6/6)
Belt (6/7)  TB (5/9) TB (28/28) FDI (6/6)
BR (5/6) IS (3/7) PS (8/26) ADM (6/6)
BB (5/7) Delt (3/8) FCR (25/27)  PS (4/5)
PS (5/7) BR (5/7)  RF (3/3)
  FCR (4/5) VM(1/1)  
PS (5/8) LPS (4/5)
  BB (4/9) LPS (12/26)  
ADM = abductor digiti minimi; BB = biceps brachii; BR = brachioradialis; Delt = deltoid; EIP = extensor indicis proprius; FDI = first dorsal interosseous; FCR = flexor carpi radialis; IS = infraspinatus; PS = paraspinals; PT = pronator teres; TB = triceps brachii

Extensor digitorum communis was rarely positive in C7 (3/17) or C6 (1/5). Paraspinals were usually positive except in C7 (8/26). Because of overlap, C6 mimicked C5 as often as it did C7, and these levels may be difficult to limit to a single root electrodiagnostically. — Michael Rubin

Dr. Rubin Professor of Clinical Neurology, New York Presbyterian Hospital-Cornell Campus.


1. Levin KH, et al. Neurology. 1996;46:1022-1025.