title: Electrical stimulation for intraoperative evaluation of thoracic pedicle screw placement.
abstract: METHODS
  Thoracic pedicle screws were stimulated electrically while recording electromyography (EMG) activity in associated muscle groups intraoperatively. Screw position was then evaluated after surgery using computed tomography (CT). The CT results were compared with evoked EMG threshold values.
  
  
  OBJECTIVE
  To report our experience with pedicle screw stimulation in thoracic vertebrae in 22 patients who underwent thoracic level spinal instrumentation from May 1999 to March 2001.
  
  
  BACKGROUND
  Pedicle screw stimulation for intraoperative assessment of screw placement has been reported in lumbosacral spinal procedures. Evoked EMG thresholds >10 or 11 mA are associated with increased probability of vertebral cortex violation and postoperative complications. Thresholds >15 mA provide a 98% confidence of accurate screw positioning on postoperative CT scans.
  
  
  METHODS
  Evoked EMG activity was recorded from ulnar carpal flexors, intercostals, or abdominal muscle groups, depending on the level of screw placement. Postoperative CT scans were read by a staff orthopedic spine surgeon, a senior resident in orthopedics, and a musculoskeletal radiologist.
  
  
  RESULTS
  Results of 87 screws are reported. Five screws (5.7%) showed penetration on postoperative CT scans. Six screws (6.9%) had stimulation thresholds < or =11 mA, of which three showed cortical breakthrough. Of the 81 screws with thresholds >11 mA, 79 (97.5%) were within the vertebra. No postoperative neurologic complications were noted in any of the 22 patients.
  
  
  CONCLUSIONS
  These results are consistent with previous studies of lumbosacral pedicle screws. In this series, stimulation thresholds >11 mA have a 97.5% negative predictive value, suggesting that cortical violation is highly unlikely. Although judgment of screw placement should not depend solely on stimulation thresholds, pedicle screw stimulation may provide rapid and useful intraoperative information on screw placement during procedures involving the use of thoracic pedicle screws.
authors.affiliation: Department of Otolaryngology/Oregon Hearing Research Center, Portland, Oregon, USA.
authors.forename: Yong-bing
authors.initials: YB
authors.lastname: Shi
authors.forename: Michael
authors.initials: M
authors.lastname: Binette
authors.forename: William H
authors.initials: WH
authors.lastname: Martin
authors.forename: James M
authors.initials: JM
authors.lastname: Pearson
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hart
mesh_terms: D001863:Bone Screws / Q000009:adverse effects; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D006801:Humans; D007432:Intraoperative Period; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods*; D011183:Postoperative Complications / Q000209:etiology / Q000517:prevention & control; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012684:Sensory Thresholds; D013122:Spinal Diseases / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed