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

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 new postoperative 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.