Monitoring of lumbosacral nerve roots during spinal instrumentation.

A technique is described for intraoperative, multimodality electrophysiologic monitoring of the spinal cord and lumbosacral nerve roots (cauda equina). Simultaneous monitoring with the techniques of electromyography, compound muscle action potentials, and somatosensory evoked potentials is found to provide highly useful information to the surgeon during lumbar spine instrumentations. Compound muscle action potential recordings are used to identify nerve roots in the lumbosacral region, especially when visual identification of the nerve is hindered by scarring or distortion of the anatomy. Electromyography continuously monitors nerve roots at risk by revealing neurotonic discharges when the nerve roots are irritated during surgical dissection or placement of the fixation device. The early warning provided by this technique enables the surgeon to avoid irreversible neurologic damage.