Combined Monitoring of Motor (MEPs) and Somatosensory Evoked Potentials (SEPs) in Orthopaedic Spinal Surgery

University Hospital, Queen's Medical Centre, Nottingham, UK

PURPOSE: To demonstrate possible advantages of combined (motor and sensory) versus single modality monitoring and its effects on intraoperative management of the patient and, to investigate risk factors for postoperative neurological sequelae.

METHODS: Recording lower limb MEPs to multi-pulse transcranial electrical stimulation (TES) and tibial nerve SEPs was attempted in 112 operations in 85 patients (71/85 with spinal deformity and 14 with miscellaneous spinal disorders).

RESULTS: Combined MEP and SEP monitoring was successfully achieved in 92 (82%) operations; in 2 operations only MEPs were obtainable and in 15 only SEPs. Significant EP changes occurred in one or both modalities in 14 patients; in association with instrumentation (9/14) or systemic changes (5/14). After appropriate remedial measures, SEPs recovered either fully or partially in all cases (7/7) and MEPs in 7/13. New deficits were present post-operatively in 5 of the 14 patients with abnormal EPs, including 3 in whom SEPs had recovered after remedial measures. Normal MEPs, but not SEPs, at the end of the operation correctly predicted the absence of new motor deficits. Post-operative neurological complications were more frequent in patients with miscellaneous spinal disorders and pre-existing neurological deficits.

CONCLUSIONS: Combined MEP and SEP monitoring is superior to single modality techniques in improving both the sensitivity and predictions of monitoring in spinal surgery. This method may enhance the impact of neuromonitoring on intraoperative management of the patient and favourably influence neurological outcome.