Saphenous Nerve Somatosensory Evoked Potentials A Novel Technique to Monitor the Femoral Nerve During Transpoas Lumbar Lateral Interbody Fusion

Study Design. A retrospective analysis of a case series was performed. Objective. To describe a novel technique to monitor femoral nerve function by analyzing the saphenous nerve somatosensory evoked potential (SSEP) during transpsoas surgical exposures of the lumbar spine. Summary of Background Data. During transpsoas direct lateral approaches to the lumbar spine, electromyography monitoring is frequently advocated; however, sensory and motor neurological complications are still being reported. Femoral nerve injury remains a feared complication at the L3-L4 and L4-L5 levels. The current neurophysiological monitoring modalities are not specific or sensitive enough to predict these injuries after the retractors are placed. The authors have developed a technique that is hypothesized to reduce femoral nerve injuries caused by retractor compression by adding saphenous nerve SSEPs to their neurophysiological monitoring paradigm. Methods. Institutional review board approval was granted for this study and the medical records along with the intraoperative monitoring reports from 41 consecutive transpsoas lateral interbody fusion procedures were analyzed. The presence or absence of intraoperative changes to the saphenous nerve SSEP was noted and the postoperative symptoms and physical examination findings were noted. Results. SSEP changes were noted in 5 of the 41 surgical procedures, with 3 of the patients waking up with a femoral nerve deficit. None of the patients with stable SSEP's developed sensory or motor deficits postoperatively. No patient in this series demonstrated intraoperative electromyography changes indicative of an intraoperative nerve injury. Conclusion. Saphenous nerve SSEP monitoring may be a beneficial tool to detect femoral nerve injury related to transpsoas direct lateral approaches to the lumbar spine.