title: Accuracy of thoracic vertebral body screw placement using standard fluoroscopy, fluoroscopic image guidance, and computed tomographic image guidance: a cadaver study.
abstract: METHODS
  A surgical simulation study in human cadaver spine specimens was conducted to evaluate the accuracy of thoracic vertebral body screw placement using four different intraoperative imaging techniques.
  
  
  OBJECTIVE
  To compare standard fluoroscopy, fluoroscopy-based image guidance with two different referencing methods, and computed tomography-based image guidance by the measuring the time required for screw placement, the radiation exposure to specimen and surgeon, and the accuracy of screw position in the thoracic spine.
  
  
  BACKGROUND
  Image guidance provides additional anatomic information to the surgeon and may improve safety of technically difficult surgical procedures. The placement of screws in the thoracic spine is a technically demanding procedure in which inaccurate screw positioning places the spinal cord, nerve roots, and paraspinal structures such as the aorta and pleural space at risk for injury. Image-guided surgery may improve the accuracy of thoracic screw placement.
  
  
  METHODS
  Using four different intraoperative imaging methods, two experienced surgeons placed 337 vertebral body screws through the pedicles of thoracic vertebrae in 20 human cadaver thoracic spine specimens. The specimens then were examined with radiographs, computed tomography, and anatomic dissection to determine screw position. Measurements included procedure setup and screw insertion time, radiation exposure to the specimen, the surgeon's hand, the surgeon's body, frequency, direction, and magnitude of screw perforation through the cortical margins of thoracic vertebrae.
  
  
  RESULTS
  As compared with surgery using standard fluoroscopy, fluoroscopy-based image guidance that uses multiple reference marks and computed tomography-based image guidance improves the accuracy of thoracic vertebral body screws, but increases the time required for screw placement and the specimen radiation exposure. Exposure to radiation is minimal at the surgeon's body level and dependent on surgical technique at the surgeon's hand level. Screw perforation occurs most frequently in the lateral direction.
  
  
  CONCLUSIONS
  Fluoroscopy-based image guidance that uses only a single reference marker for the entire thoracic spine is highly inaccurate and unsafe. Systems with registration based on the instrumented vertebrae provide more accurate placement of thoracic vertebral body screws than standard fluoroscopy, but expose the patient to more radiation and require more time for screw insertion.
authors.affiliation: Department of Orthopedics and Sports Medicine, University of Washington, Seattle, Washington, USA. mirza@u.washington.edu
authors.forename: Sohail K
authors.initials: SK
authors.lastname: Mirza
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Wiggins
authors.forename: Charles
authors.initials: C
authors.lastname: Kuntz
authors.forename: Julie E
authors.initials: JE
authors.lastname: York
authors.forename: Carlo
authors.initials: C
authors.lastname: Bellabarba
authors.forename: Mark A
authors.initials: MA
authors.lastname: Knonodi
authors.forename: Jens R
authors.initials: JR
authors.lastname: Chapman
authors.forename: Christopher I
authors.initials: CI
authors.lastname: Shaffrey
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001863:Bone Screws; D002102:Cadaver; D005471:Fluoroscopy / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*