Spinal cord monitoring: Current state of the art

Spinal cord monitoring continues to play a role in the operative treatment of spinal disorders. Its use has grown well beyond the research laboratories and limited clinical application that was seen 10 years ago. Intraoperative assessment has become a standard of care in certain spinal surgeries. It is widely used in the surgical correction of scoliosis. The SSEP remains the basis for monitoring protocols. SSEPs are capable of providing reliable information concerning various neurophysiologic events during surgery. These data are readily obtained for a wide array of patients. Techniques used to elicit and record the SSEP are minimally invasive. As stated earlier, newer monitoring methods are used as adjuncts to, not instead of, the SSEP. Motor evoked potentials have remained at the forefront of research and development in the area of intraoperative monitoring this past decade. Motor tract assessment is recommended for surgeries that place the spinal cord at risk. Debate and discussion continue in this area in an effort to determine the optimal technique. Transcranial methods of stimulation have been proven viable; work is now needed to make them practical. Perhaps most importantly, response criteria must be developed to determine what constitutes a significant change in these data. Spinal cord stimulation is more widely used than either transcranial techniques. This method is more easily incorporated into an existing protocol. Response criteria have been determined and proved sensitive. The origins of the response are now regarded as largely sensory. This factor should not negate the use of spinal cord stimulation. The method appears sensitive to neurologic changes before the SSEP, thereby increasing the timely identification of potentially reversible deficits. The addition of techniques to assess nerve root function has increased monitoring applications in the area of degenerative spine disease. Use of triggered EMG monitoring for placement of pedicle screws has become commonplace in segmental instrumentation procedures. Spontaneous EMG monitoring is also gaining wide acceptance in the surgical arena. Further studies are needed, however, to determine more fully the significance of this EMG activity. Further research in this area needs to focus on methods for determining adequacy of decompression. The dermatomal SSEP has not proved useful in the operative setting. The EMG techniques in use do not provide any information that is predictive of postoperative improvement in neurologic status. Electrically triggered EMG testing that is performed before and after individual nerve root decompression may be able to provide objective data. Intraoperative monitoring techniques will continue to evolve to meet the needs of those involved in spinal surgery. The goal is to minimize neurologic risk.