title: Thoracic pedicle screw placement: analysis using anatomical landmarks without image guidance.
abstract: METHODS
  Prospective laboratory study analyzing the technique of pedicle screw placement in a cadaveric model.
  
  
  OBJECTIVE
  To determine whether a freehand technique without image guidance can be used to safely place pedicle screws in the thoracic spine.
  
  
  BACKGROUND
  The use of thoracic pedicle screws for the treatment of spinal deformity has been gaining increased acceptance among surgeons. Although these implants improve deformity correction, there is still concern regarding the risks to neurological and vascular structures and regarding the experience level needed to use this implant. This study was designed to determine whether these implants could be placed safely without imaging modalities.
  
  
  METHODS
  Six fresh cadaveric specimens were instrumented from vertebral segments T4-T11. Ninety-six screws were placed along the anatomical axis of the pedicle. Pedicles were dissected to determine the wall violations, the position of neural structures, and the lateral coverage of the pedicle by the rib head.
  
  
  RESULTS
  Ninety-seven percent of screws had less than 1 mm of wall violation, with 84 screws (87.5%) fully contained within the pedicle. Four screws (4.16%) violated the medial cortex. No violations occurred superiorly, inferiorly, or anteriorly. Nerve roots were in contact with the inferior pedicle wall at all levels. The average distance from nerve to the superior pedicle ranged from 3.85 to 5.04 mm.
  
  
  CONCLUSIONS
  Placing pedicle screws along the anatomical axis without image guidance produced a low level of pedicle wall disruption. This technique uses a reproducible start point at each level, and the results are equal to or better than those of other cadaveric studies that have used guidance systems.
authors.affiliation: Naval Medical Center Portsmouth, Virginia, USA. melliott@childrenscentalcal.org
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Elliott
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Slakey
mesh_terms: D000328:Adult; D001863:Bone Screws; D002102:Cadaver; D005471:Fluoroscopy; D006801:Humans; D019637:Orthopedic Procedures / Q000009:adverse effects / Q000379:methods*; D013121:Spinal Curvatures / Q000601:surgery*; D013904:Thoracic Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery*