title: Electromagnetic field-based image-guided spine surgery part two: results of a cadaveric study evaluating thoracic pedicle screw placement.
abstract: METHODS
  Human cadaveric.
  
  
  OBJECTIVE
  Compare the accuracy of electromagnetic field (EMF)-based image-guided thoracic pedicle screw insertion to conventional techniques using anatomic landmarks and fluoroscopy.
  
  
  BACKGROUND
  Image-guided surgical systems that aid in spinal instrumentation seek to minimize radiation exposure and improve accuracy. EMF image guidance was developed as an alternative to optical tracking to eliminate potential line of sight issues.
  
  
  METHODS
  Four fresh-frozen human cadavers were randomly allocated into two groups. Pedicle screws were inserted from T1 to T12 using anatomic landmarks and fluoroscopy in group 1 and image guidance in group 2. Insertion and fluoroscopy time were recorded. Anatomic dissections were performed to assess screw placement.
  
  
  RESULTS
  Image guidance placed 92% of thoracic pedicle screws safely, and conventional fluoroscopy placed 90% safely. The average degree of perforation was 2.4 mm with conventional fluoroscopy and 1.7 mm with image guidance (P = 0.055). Fluoroscopic time per screw was 5.9 seconds for conventional fluoroscopy and 3.6 seconds for image guidance (P = 0.045). Insertion time per screw was 4.35 minutes for conventional fluoroscopy and 2.98 minutes for image guidance (P = 0.007). However, when set-up time and image capture time were taken into account, the total insertion time per screw was not significantly different between the two groups.
  
  
  CONCLUSIONS
  Our study has shown that EMF image-guided thoracic pedicle screw placement results in a similar incidence of safely placed screws as does conventional fluoroscopy. When set-up time and image-capture time were factored in for image guidance, the average time to insert a pedicle screw was equal for both techniques. The use of EMF image guidance significantly reduced fluoroscopic time and thus radiation exposure per screw compared with conventional fluoroscopic techniques.
authors.affiliation: University of California San Francisco-Fresno, Fresno, CA, USA. eversosaggy@cs.com
authors.forename: H C
authors.initials: HC
authors.lastname: Sagi
authors.forename: R
authors.initials: R
authors.lastname: Manos
authors.forename: S-C
authors.initials: SC
authors.lastname: Park
authors.forename: R
authors.initials: R
authors.lastname: Von Jako
authors.forename: N R
authors.initials: NR
authors.lastname: Ordway
authors.forename: P J
authors.initials: PJ
authors.lastname: Connolly
mesh_terms: D000704:Analysis of Variance; D001863:Bone Screws; D002102:Cadaver; D016009:Chi-Square Distribution; D004574:Electromagnetic Fields; D005471:Fluoroscopy / Q000379:methods; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D011897:Random Allocation; D015203:Reproducibility of Results; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D025321:Surgery, Computer-Assisted / Q000379:methods; D013904:Thoracic Vertebrae / Q000601:surgery*; D013997:Time Factors