SPINE Volume 35, Number 26S, pp S368 –S374 ©2010, Lippincott Williams & Wilkins Electromyographic Monitoring and Its Anatomical Implications in Minimally Invasive Spine Surgery Juan S. Uribe, MD, Fernando L. Vale, MD, and Elias Dakwar, MD Study Design. Literature review. Objective. The objective of this article is to examine current intraoperative electromyography (EMG) neurophys- iologic monitoring methods and their application in mini- mally invasive techniques. We will also discuss the recent application of EMG and its anatomic implications to the minimally invasive lateral transpsoas approach to the spine. Summary of Background Data. Minimally invasive techniques require that the same goals of surgery be achieved, with the hope of decreased morbidity to the patient. Unlike standard open procedures, direct visual- ization of the anatomy is decreased. To increase the safety of minimally invasive spine surgery, neurophysio- logical monitoring techniques have been developed. Methods. Review of the literature was performed us- ing the National Center for Biotechnology Information databases using PUBMED/MEDLINE. All articles in the English language discussing the use of intraoperative EMG monitoring and minimally invasive spine surgery were reviewed. The role of EMG monitoring in special reference to the minimally invasive lateral transpsoas ap- proach is also described. Results. In total, 76 articles were identified that dis- cussed the role of neuromonitoring in spine surgery. The majority of articles on EMG and spine surgery discuss the use of intraoperative neurophysiological monitoring (IOM) for safe and accurate pedicle screw placement. In general, there is a paucity of literature that pertains to intraoperative EMG neuromonitoring and minimally inva- sive spine surgery. Recently, EMG has been used during minimally invasive lateral transpsoas approach to the lumbar spine for interbody fusion. The addition of EMG to the lateral approach has contributed to decrease the com- plication rate from 30% to less than 1%. Conclusion. In minimally invasive approaches to the spine, the use of EMG IOM might provide additional safety, such as percutaneous pedicle screw placement, where visualization is limited compared with conven- tional open procedures. In addition to knowledge of the anatomy and image guidance, directional EMG IOM is crucial for safe passage through the psoas muscle during the minimally invasive lateral retroperitoneal approach. Key words: extreme lateral interbody fusion (XLIF), psoas, lumbar plexus, neuromonitoring, electromyography (EMG), minimally invasive. Spine 2010;35:S368 –S374 Spinal surgery includes a vast array of techniques and approaches to accomplish the intended goals of decom- pression, realignment, and stabilization. As with other surgical specialties, the recent trend has been to perform these procedures minimally invasively. Minimally inva- sive techniques require that the same goals of surgery be achieved, with the hope of decreased morbidity to the patient. Unlike standard open procedures, direct visual- ization of the anatomy is decreased. To increase the safety of minimally invasive spine surgery, neurophysio- logical monitoring techniques have been developed. Intraoperative neurophysiological monitoring (IOM) methods, namely, somatosensory and motor-evoked po- tentials (SSEP and MEP, respectively) and free-run and evoked (triggered) electromyography (frEMG and tEMG, respectively), have aided in the intraoperative identification and correction of neural impingement while decreasing the prevalence of nerve injury. 1–24 These methods are used to monitor the spinal cord (de- scending rostral column corticospinal and ascending dorsal column somatosensory tracts), spinal nerve roots, cauda equina, conus medullaris, and more recently, the lumbar plexus. 8,10,20,21 Nash et al introduced SSEP monitoring for nerve in- jury detection and avoidance during scoliosis surgery in 1977. 25 Subsequent publications have shown the sensi- tivity and specificity of multimodal neuromonitoring of the spinal cord and nerve roots during the surgical treat- ment of spinal trauma, 26,27 tumors, 28 –33 degenerative and idiopathic scoliosis, 15,16,19,25,34–38 placement of pedicle screws, 2,3,9,39 – 42 and for testing the degree of nerve root function in posterior decompressive proce- dures. 43,44 Advanced neurophysiologic monitoring has mainly been used in complex procedures, which are more commonly performed with open expo- sures. 8,10,22,45 Outside of EMG screw testing in percuta- neous pedicle screw placement, 41 the role of intraopera- tive neurophysiologic monitoring in minimally invasive interbody fusion approaches has been less well studied or defined. 46–48 The objective of this article is to examine current intraoperative EMG neurophysiologic monitor- ing methods and their application in minimally invasive techniques. The recent application of EMG to the mini- mally invasive lateral transpsoas approach to the spine is also discussed. Methods Review of the literature was performed using the National Cen- ter for Biotechnology Information databases using PUBMED/ MEDLINE. Keywords included intraoperative, neurophysio- logic, monitoring, somatosensory, motor, evoked potentials, From the Department of Neurosurgery and Brain Repair, University of South Florida, Tampa, FL. Acknowledgment date: September 28, 2010. Revision date: October 15, 2010. Acceptance date: October 15, 2010. The device(s)/drug(s) is/are FDA-approved or approved by correspond- ing national agency for this indication. No funds were received in support of this work. One or more of the author (s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript: e.g., honoraria, gifts, consultancies, royalties, stocks, stock options, decision making position. Address correspondence and reprint requests to Juan S. Uribe, MD, University of South Florida, 2a Columbia Drive, 7th floor, Tampa, FL 33606; E-mail: juansuribe@gmail.com S368