Motor nerve root monitoring during percutaneous transforaminal endoscopic sequestrectomy under general anesthesia for intra- and extraforaminal lumbar disc herniation

Abstract

Introduction Percutaneous transforaminal endoscopic sequestrectomy (PTFES) for intram and extraforaminal lumbar disc herniation (IHLD and EHLD) is usually performed under local anesthesia because the patient's full cooperation is necessary during surgery in order to reduce morbidity. This puts intraoperative stress on both the patient and the surgeon. The present study was performed to assess the safety and efficacy of performing PTFES under general anesthesia using a new protocol with continuous intraoperative neurophysiological monitoring (IOM). Patients and methods Twenty-five patients with IHLD and/or EHLD were treated by PTFES under general anesthesia without neuromuscular blocking agents. Free-run electromyography (EMG) recordings from characteristic muscles were monitored for the nerve root exiting through the intervertebral foramen at the level of surgery as well as those immediately above and below this level. The recorded potentials were visualized and analyzed on the monitoring screen. Additionally, the EMG activity was played to the surgeon via loudspeakers. Results EMG-assisted endoscopic sequestrectomy was successfully completed in all 25 cases. Three patients showed complex repetitive discharge patterns already before the actual procedure, but these normalized upon removal of the sequester. Abnormal EMG changes in the form of intraoperative isolated spikes, phasic bursts, or tonic trains were recorded in 17 of the 25 cases. These occurred during placement of the endoscopic working channel in the area of the neuroforamen in 12 cases and during removal of the sequester in 6 cases. Spikes and bursts were evoked by direct contact with the nerve root or indirectly through traction or compression. Tonic discharge patterns, on the other hand, correlated with more severe mechanical stress caused for instance by compression or traction when the nerve root was fixed in the neuroforamen by the sequester. Conclusions PTFES under general anesthesia is a safe and easy-to-perform technique for surgical management of intra- and/or extraforaminal lumbar disc herniation if combined with intraoperative neurophysiological monitoring. General anesthesia reduces intraoperative stress to a minimum, so that a larger number of patients may benefit from this minimally invasive procedure in future.