title: Triggered EMG Potentials in Determining Neuroanatomical Safe Zone for Transpsoas Lumbar Approach: Are They Reliable?
abstract: METHODS
  In vivo analysis in swine model.
  
  
  OBJECTIVE
  The purpose of this study was to determine the accuracy of triggered EMG (t-EMG) and its reliability in lateral lumbar interbody fusions surgery. We also aim to document changes in psoas muscle produced during the approach.
  
  
  BACKGROUND
  Lateral lumbar interbody fusions is preferred over direct anterior approach because of lower complications, blood loss, and shorter recovery time. Threshold-EMGs are utilized for real-time feedback about nerve location; however, neurological deficits are widely reported, and are unique to this approach. Multiple factors have been hypothesized including neuropraxia from retractors and compression from psoas hematoma/edema. The variable reports of neurological complication even with t-EMGs indicate the need to study them further.
  
  
  METHODS
  Eight swines underwent left-sided retroperitoneal approach. The nerve on the surface of the psoas was identified and threshold-EMGs were obtained utilizing a ball-tip, and needle probe. First EMG and threshold responses required to elicit 20-μV responses were recorded for 2 mm incremental distances up to 10 mm. In the second part, a K-wire was inserted into the mid-lumbar disc space, and a tubular retractor docked and dilated adequately. Postmortem CT scans were carried out to evaluate changes in psoas muscle.
  
  
  RESULTS
  A t-EMG stimulus threshold of <5 mA indicates a higher probability that the probe is close to or on the nerve, but this was not proportional to the distance suggesting limitations for nerve mapping. Negative predictive value of t-EMGs is 76.5% with the ball-tipped probe and 80% with the needle probe for t-EMG ≥10 mA and indicates that even with higher thresholds, the nerve may be much closer than anticipated. Postoperative hematoma was not seen on CT scans.
  
  
  CONCLUSIONS
  Threshold measurements are unreliable in estimating distance from the nerve in an individual subject and higher values do not always correspond to a 'safe zone."
  
  
  METHODS
  5.
authors.affiliation: Department of Pediatric Orthopedics, Cohen's Children Medical Center, New Hyde Park, NY.
authors.forename: Vishal
authors.initials: V
authors.lastname: Sarwahi
authors.affiliation: Montefiore Medical Center, Bronx, NY.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Pawar
authors.affiliation: Department of Orthopaedic Surgery, Montefiore Medical Center, Bronx, NY.
authors.forename: Etan
authors.initials: E
authors.lastname: Sugarman
authors.affiliation: Department of Neurology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY.
authors.forename: Alan D
authors.initials: AD
authors.lastname: Legatt
authors.affiliation: Department of Pediatric Orthopedics, Cohen's Children Medical Center, New Hyde Park, NY.
authors.forename: Aviva
authors.initials: A
authors.lastname: Dworkin
authors.affiliation: Department of Radiology, Montefiore Medical Center, Bronx, NY.
authors.forename: Beverly
authors.initials: B
authors.lastname: Thornhill
authors.affiliation: Department of Epidemiology and Population Health, The Albert Einstein College of Medicine, Bronx, NY.
authors.forename: Yungtai
authors.initials: Y
authors.lastname: Lo
authors.affiliation: Department of Pediatric Orthopedics, Cohen's Children Medical Center, New Hyde Park, NY.
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Wendolowski
authors.affiliation: Department of Pediatric Orthopedics, Cohen's Children Medical Center, New Hyde Park, NY.
authors.forename: Rachel C
authors.initials: RC
authors.lastname: Gecelter
authors.affiliation: Department of Anesthesiology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY.
authors.forename: Marina
authors.initials: M
authors.lastname: Moguilevitch
mesh_terms: D000818:Animals; D004576:Electromyography / Q000379:methods / Q000592:standards*; D008159:Lumbar Vertebrae / Q000033:anatomy & histology* / Q000601:surgery*; D016658:Psoas Muscles / Q000033:anatomy & histology* / Q000601:surgery*; D015203:Reproducibility of Results; D013123:Spinal Fusion / Q000379:methods / Q000592:standards*; D013552:Swine