title: Intraoperative decrease in amplitude of somatosensory-evoked potentials of the lower extremities with interbody fusion cage placement during lumbar fusion surgery.
abstract: METHODS
  A retrospective analysis was performed.
  
  
  OBJECTIVE
  To characterize neurophysiological data of patients who had a decrease in amplitude of somatosensory-evoked potentials (SSEP) of the lower extremities secondary to interbody fusion cage placement during lumbar fusion surgery with no alert of the electromyography (EMG).
  
  
  BACKGROUND
  The most consistently used and studied modalities of neurophysiological monitoring during spine surgery are SSEPs, motor-evoked potentials (MEPs), and EMG. In general, it is accepted that MEPs along with SSEPs are used to detect spinal cord injury and EMGs are used to detect nerve root injury.
  
  
  METHODS
  The medical records of a consecutive series of 115 patients who had undergone a transforaminal lumbar interbody fusion (TLIF) procedure in which SSEPs, MEPs, and EMGs were utilized for neurophysiological monitoring were retrospectively reviewed.
  
  
  RESULTS
  One hundred fifteen cases of TLIF procedures were reviewed. The follow-up was 2 years after the last procedure. A total of 5 cases that demonstrated intraoperative SSEP changes were found. The age range for these cases was from 39 to 81 years (mean age, 61 yr). All 5 patients developed SSEP changes that were secondary to interbody fusion cage placement. All 5 cases demonstrated reversal of the SSEP changes to baseline after removal of the interbody cage. Three of these cases had no new postoperative neurological findings. However, given that these 3 cases of SSEP change were associated with a surgical event that improved secondary to an intervention (in this case removal of the interbody cage), those cases were classified as presumed positive. Two of the 5 cases were in fact associated with a new postoperative neurological deficit.
  
  
  CONCLUSIONS
  To our knowledge this study demonstrates the first reported SSEP alerts that were associated with a posterior lumbar interbody cage placement without a corresponding EMG alert.
authors.affiliation: Department of Orthopaedic Surgery, University of Southern California, Keck School of Medicine, Los Angeles, CA, USA.
authors.forename: Jan William
authors.initials: JW
authors.lastname: Duncan
authors.forename: Richard Anthony
authors.initials: RA
authors.lastname: Bailey
authors.forename: Rocio
authors.initials: R
authors.lastname: Baena
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000379:methods*; D013997:Time Factors