The use of dermatomal evoked responses during surgical procedures that use intrapedicular fixation of the lumbosacral spine

Monitoring of electrophysiologic function during intrapedicular fixation of the lumbosacral spine can be useful because this fixation technique has been associated with a significant number of postoperative radicular complications. Somatosensory evoked potentials (SEPs) traditionally have been used to monitor neurologic function during spinal instrumentation procedures. A case is presented of an intrapedicular fixation procedure that was monitored with SEPs and that resulted in false-negative SEP findings. This result suggests that SEPs may not be a sensitive enough monitoring tool for detecting compromise of single root function, and as a result, other monitoring techniques should be used. Dermatomal somatosensory evoked potentials (DSEPs) have been reported to be useful in this regard. To test their usefulness, 81 lumbosacral intrapedicular fixation procedures were monitored with DSEPs. Repeatable responses were obtained from all but one of the patients. The responses were sensitive to the compromise of root function. Predictions of postoperative outcome were dependent only on the responses at closing and not on changes that occurred during surgery.