title: Anatomical considerations for subaxial (C2) pedicle screw placement: a radiographic study with computed tomography in 93 patients.
abstract: METHODS
  Radiographic study.
  
  
  OBJECTIVE
  More detailed anatomical knowledge of the C2 pedicle is required to optimize and minimize the risk of screw placement. The aim of this study was to evaluate the linear and angular dimensions of the true C2 pedicle using axial computed tomography.
  
  
  BACKGROUND
  Although earlier studies have analyzed the anatomy of the C2 pars interarticularis, little attention has been focused on the dimensions of the C2 pedicle.
  
  
  METHODS
  Ninety-three patients (47 males, 46 females; mean age 48.4 y) who had previous cervical spinal computed tomography imaging were evaluated for this study. Axial images of the C2 pedicle were selected and the following pedicle parameters were determined: pedicle width (the mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis) and pedicle transverse angle (PTA, ie, the angle between the pedicle axis and the midline of the vertebral body).
  
  
  RESULTS
  The overall mean pedicle width was 5.8+/-1.2 mm. The mean pedicle width in male patients (6.0+/-1.3 mm) was greater than that in the female patients (5.6+/-1.1 mm). This difference was not found to be statistically significant (P=0.679). The overall mean PTA was 43.9+/-3.9 degrees. The mean PTA in male patients was 43.2+/-3.8 degrees, whereas that in female patients was 44.7+/-3.7 degrees.
  
  
  CONCLUSIONS
  Given the significant variability in pedicle widths and the need for precise trajectory planning in pedicle cannulation, preoperative planning is absolutely mandatory. A significant percentage of patients have pedicle widths that may not accommodate screw fixation. In addition, the angle of entry into the C2 pedicle must be carefully measured for safe instrumentation at this level.
authors.affiliation: Department of Neurological Surgery, University of California, CA, USA.
authors.forename: Zachary A
authors.initials: ZA
authors.lastname: Smith
authors.forename: Simona
authors.initials: S
authors.lastname: Bistazzoni
authors.forename: Adebukoa
authors.initials: A
authors.lastname: Onibokun
authors.forename: Nan-Fu
authors.initials: NF
authors.lastname: Chen
authors.forename: Marco
authors.initials: M
authors.lastname: Sassi
authors.forename: Larry T
authors.initials: LT
authors.lastname: Khoo
mesh_terms: D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000601:surgery*; D001863:Bone Screws; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008297:Male; D011859:Radiography; D013123:Spinal Fusion / Q000379:methods*