Feasibility of Nerve Stimulator as a Supplemental Aid for Lumbar Transforaminal Epidural Block

BACKGROUND The purpose of this study was to evaluate the clinical feasibility of an electric nerve stimulator in a lumbar transforaminal epidural block. METHODS Using an electric nerve stimulator, transforaminal epidural blocks were performed in 105 segments of 49 patients who presented with lower back pain with radiating pain to lower extremities. The contrast medium was injected to delineate the nerve root after positioning an insulated needle at the intervertebral foramen under fluoroscopic guidance. Then, the nerve root was electrically stimulated with the insulated needle to confirm whether or not the same radiating pain was evoked. RESULTS Of the 105 foraminal segments, the same radiating pain was evoked at 0.5 mAh in 47 segments (44.8%), at 1.0 mAh in 22 (21.0%), at 1.5 mAh in 3 (2.9%), at 2.0 mAh in 15 (14.3%), at 2.5 mAh in 4 (3.8%), and at 3.0 mAh in 5 (4.8%). No response was observed in 9 segments (8.6%). The fluoroscopy revealed successful positioning of the needle in the patients with an evoked radiating pain over 2.0 mAh. The visual analogue scale (VAS) obtained for pain improved from a mean of 7.5 to 2.7 after the block (p = 0.001). In the 9 cases without response to electrical stimulation, the patients showed an improvement on VAS from 7.8 to 3.4 (p= 0.008) also. CONCLUSIONS A nerve stimulator can help to predict the accuracy of needle positioning as a supplemental aid for a successful lumbar transforaminal epidural block. It is sufficient to initiate a proper stimulation amplitude of the nerve at 2 mAh.