A Prospective, Non-randomized, Multicenter Evaluation of the Utility of Transcutaneous Stimulation of the Lumbosacral Nerve Roots During XLIF® and Its Relationship to Postoperative Nerve Health

The utility of NVM5 neuromonitoring by stimulating within the surgical site during XLIF has been previously demonstrated; however, it is possible that depending on the site of injury, this method of monitoring may stimulate nerves at a location that is distal to the site of injury along the nerve conduction pathway. In this example, the site of injury would not disrupt the stimulus and a normal muscle response may occur, providing a false negative result. With this in mind, it has been hypothesized that more accurate information may be gathered by stimulating the lumbar roots or spinal nerves cranial to the surgical site and recording the subsequent muscle response in the lower limbs. Using this technique, the response to the stimulus would traverse the surgical site, including the site of any nerve injury. Currently, the only described method of stimulating cranial to the surgical site is with transcranial motor evoked potentials (tcMEP); stimulating the lumbosacral nerve roots locally has not been demonstrated. Though tcMEP monitoring is a well-documented technique, there are several limitations associated with its use. For example, tcMEP requires adherence to total intravenous anesthesia (TIVA), thereby restricting the use of inhalational agents. This restriction may require additional training and coordination with the anesthesiologist, as well as added cost to the hospital.6 Additional challenges with tcMEP include the requirements for high voltage stimulation to successfully transmit a stimulus across the skull. In rare instances this can cause seizures, tongue lacerations, and other complications. Finally, due to inclusion of the central nervous system, monitoring with tcMEP may be less reproducible and specific than a more localized stimulation.

To address these challenges, recent adaptations to standard MEP and EMG monitoring protocols have used local stimulation of the lumbosacral nerve roots at the level of the conus, with recorded responses from the relevant innervated muscle groups of the lower limbs. Early experience using this technique has shown the feasibility and reproducibility of obtaining reliable baseline and longitudinal responses throughout a surgical procedure, and incorporation of this monitoring modality has become common practice at certain surgical sites performing XLIF, although determination of clinically meaningful changes in those responses have yet to be determined.