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

Silverstein, Justin MS, CNIM*,†; Mermelstein, Laurence MD†,‡; DeWal, Hargovind MD†,‡; Basra, Sushil MD†,‡

doi: 10.1097/BRS.0000000000000357

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.

Level of Evidence: 4

A retrospective case series was reviewed examining saphenous nerve somatosensory evoked potentials (SSEPs) during transpsoas lateral approaches to the lumbar spine. Saphenous nerve SSEP abnormalities correlated to postoperative femoral nerve injury. This novel technique may aid in detecting femoral nerve injury during this specific surgical approach.

*Spine Medical Services, PLLC, Commack, NY

Department of Orthopedics, NorthShore-LIJ Huntington Hospital, Huntington, NY; and

Long Island Spine Specialists, PC, Commack, NY.

Address correspondence and reprint requests to Justin Silverstein, MS, CNIM, Director of Clinical Neurophysiology, Spine Medical Services, PLLC, 763 Larkfield Rd, Ste 202, Commack, NY 11725; E-mail:

Acknowledgment date: December 30, 2013. First revision date: February 3, 2014. Second revision date: March 20, 2014. Acceptance date: March 25, 2014.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: consultancy, stocks.

© 2014 by Lippincott Williams & Wilkins