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Real-Time Continuous Intraoperative Electromyographic and Somatosensory Evoked Potential Recordings in Spinal Surgery: Correlation of Clinical and Electrophysiologic Findings in a Prospective, Consecutive Series of 213 Cases

Gunnarsson, Thorsteinn, MD, MSc*; Krassioukov, Andrei V., MD, PhD; Sarjeant, Roger, BSc, CNIM*; Fehlings, Michael G., MD, PhD, FRCSC*†

doi: 10.1097/01.BRS.0000115144.30607.E9

Study Design. Retrospective analysis of a prospectively accrued series of 213 consecutive patients who underwent intraoperative neurophysiologic monitoring with electromyography and somatosensory-evoked potentials during thoracolumbar spine surgery.

Objectives. To study the incidence of significant intraoperative electrophysiologic changes and new postoperative neurologic deficits.

Summary of Background Data. Continuous intraoperative electromyography and somatosensory-evoked potentials are frequently used in spinal surgery to prevent neural injury. However, only limited data are available on the sensitivity, specificity, and predictive values of intraoperative electrophysiologic changes with regard to the occurrence of new postoperative neurologic deficits.

Methods. We examined data on patients who underwent intraoperative monitoring with continuous lower limb electromyography and somatosensory-evoked potentials. The analysis focused on the correlation of intraoperative electrophysiologic changes with the development of new neurologic deficits.

Results. A total of 213 patients underwent surgery on a total of 378 levels; 32.4% underwent an instrumented fusion. Significant electromyograph activation was observed in 77.5% of the patients and significant somatosensory-evoked potential changes in 6.6%. Fourteen patients (6.6%) had new postoperative neurologic symptoms. Of those, all had significant electromyograph activation, but only 4 had significant somatosensory-evoked potential changes. Intraoperative electromyograph activation had a sensitivity of 100% and a specificity of 23.7% for the detection of a new postoperative neurologic deficit. Somatosensory-evoked potentials had a sensitivity of 28.6% and specificity of 94.7%.

Conclusions. Intraoperative electromyographic activation has a high sensitivity for the detection of a newpostoperative neurologic deficit but a low specificity. In contrast, somatosensory-evoked potentials have low sensitivity but high specificity. Combined intraoperative neurophysiologic monitoring with electromyography and somatosensory-evoked potentials is helpful for predicting and possibly preventing neurologic injury during thoracolumbar spine surgery. Spine 2004;29:677–684

We studied 213 patients undergoing thoracolumbar surgery and intraoperative neurophysiologic monitoring. Significant activation of electromyography occurred in 77.5%. Significant somatosensory-evoked potential changes occurred in 6.6% of the patients. The sensitivity of electromyography to detect new postoperative deficits was high, whereas specificity was low. Somatosensory-evoked potentials had low sensitivity but high specificity.

*Division of Neurosurgery, University of Toronto, Krembil Neuroscience Center, Toronto Western Hospital, Toronto, and

†Department of Surgery, University of Toronto, Toronto, Ontario, Canada.

Acknowledgment date: July 31, 2003.

First revision date: September 9, 2003.

Acceptance date: September 19, 2003.

The legal regulatory status of the device(s)/drug(s) that is/are the subject of this manuscript is not applicable in my country.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Dr. Michael G. Fehlings, Division of Neurosurgery, Spinal Program, Toronto Western Hospital, 399 Bathurst St, West Wing, 4W-499, Toronto, Ontario M5T 2S8, Canada; E-mail:

© 2004 Lippincott Williams & Wilkins, Inc.