title: Saphenous nerve somatosensory evoked potentials: a novel technique to monitor the femoral nerve during transpsoas lumbar lateral interbody fusion.
abstract: METHODS
  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.
  
  
  BACKGROUND
  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.
  
  
  CONCLUSIONS
  Saphenous nerve SSEP monitoring may be a beneficial tool to detect femoral nerve injury related to transpsoas direct lateral approaches to the lumbar spine.
  
  
  METHODS
  4.
authors.affiliation: *Spine Medical Services, PLLC, Commack, NY †Department of Orthopedics, NorthShore-LIJ Huntington Hospital, Huntington, NY; and ‡Long Island Spine Specialists, PC, Commack, NY.
authors.forename: Justin
authors.initials: J
authors.lastname: Silverstein
authors.forename: Laurence
authors.initials: L
authors.lastname: Mermelstein
authors.forename: Hargovind
authors.initials: H
authors.lastname: DeWal
authors.forename: Sushil
authors.initials: S
authors.lastname: Basra
mesh_terms: D004576:Electromyography / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D005267:Femoral Nerve / Q000502:physiology*; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D016658:Psoas Muscles / Q000294:innervation / Q000601:surgery; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000379:methods*