title: Anatomic consideration of C2 pedicle screw placement.
abstract: METHODS
  This anatomic study tested placement of C2 pedicle screws using cadaver specimens.
  
  
  OBJECTIVE
  To further assess the safety of transpedicular screw placement in the axis by comparing two surgical techniques.
  
  
  BACKGROUND
  Transpedicular screw fixation of traumatic spondylolisthesis of the axis has been described in the literature. Recently, anatomic studies and clinical applications of transpedicular screw fixation for traumatic lesions of middle and lower cervical spine have been described. No previous study assessing the safety of C2 pedicle screw placement is available.
  
  
  METHODS
  Sixteen embalmed cadaveric specimens were used for this study. In the first eight specimens (Method A), the point of entry for screw placement was chosen to be about 5 mm inferior to the superior border of C2 lamina and 7 mm lateral to the lateral border of the spinal canal. The screw direction was chosen to be about 30 degrees medial to the sagittal plane and 20 degrees cephalad to the transverse plane. A 3.5-mm cortical screw of appropriate length, determined with depth gauge, was placed bilaterally into the C2 pedicle. In the next eight specimens (Method B), the direction of the drill bit was guided directly by the medial and superior aspect of the individual C2 pedicle. Gross dissection was done to view violation of dura, nerve roots, vertebral artery, and penetration of medial, lateral, superior, and inferior cortex of the C2 pedicle. Radiographs and computed tomography scans were obtained to evaluate screw placement in the C2 pedicle.
  
  
  RESULTS
  In Method A, four screws had lateral violations into the vertebral artery. In Method B, only two cases of minimal penetration of pedicle cortex were found. No medial, superior, or inferior violation of the pedicle cortex was found in the present study.
  
  
  CONCLUSIONS
  The present anatomic study suggests that transpedicular screw fixation may be performed safely in the C2 pedicle by using the second technique. Using the first technique is not safe.
authors.affiliation: Department of Orthopaedic Surgery, Medical College of Ohio, Toledo, USA.
authors.forename: N
authors.initials: N
authors.lastname: Ebraheim
authors.forename: J R
authors.initials: JR
authors.lastname: Rollins
authors.forename: R
authors.initials: R
authors.lastname: Xu
authors.forename: W T
authors.initials: WT
authors.lastname: Jackson
mesh_terms: D001863:Bone Screws; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D013123:Spinal Fusion / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed