title: Ideal starting point and trajectory for C2 pedicle screw placement: a 3D computed tomography analysis using perioperative measurements.
abstract: BACKGROUND
  C2 pedicle screws provide stable fixation for posterior cervical fusion. Placing C2 pedicle screws is fraught with risks, and a misplaced screw can result in cortical breach of the pedicle, resulting in injury to the vertebral artery or spinal cord.
  
  
  OBJECTIVE
  We sought to identify a reproducible starting point and trajectory for C2 pedicle screw placement using three-dimensional (3D) computed tomography (CT) imaging. Our aims included identifying correct cephalad and mediolateral angles used for determining the most accurate trajectory through the C2 pedicle.
  
  
  METHODS
  A radiographic analysis of the anatomy of the C2 pedicle using CT.
  
  
  METHODS
  A random sample of 34 cervical spine CT scans in patients without medical or surgical pathology of the cervical spine.
  
  
  METHODS
  Normal anatomic measurements made in the axial and sagittal planes of the CT scans. Angles and measures in millimeters were recorded.
  
  
  METHODS
  The C2 pedicles were evaluated using CT scanning with a 3D imaging application. The ideal trajectory through each pedicle was plotted. The mediolateral and cephalad angles were measured using the midline sagittal plane and the inferior vertebral body border as references. Other measurements made were the distances through the pedicle and vertebral bodies, and the surface distances along the laminae between the isthmus and the starting point of the chosen trajectories. Other measurements involving the height of the laminae were also made. The mean values, standard deviations, and intraobserver variations are presented.
  
  
  RESULTS
  CT scans from 34 patients were reviewed. The sex of the patient did not predict angle measurements (p=.2038), so combined male and female patient measures are presented. The mean mediolateral angle measured was 29.2°, and the mean cephalad angle was 23.0°. The mean distance along the lamina surface between the isthmus and the starting point was 8.1 mm. The mean distance from the superior border of the lamina to the starting point was 5.7 mm. There were no statistically significant differences between the dataset collected in duplicate by the same observer (p=.74); as such, we present one data analysis on combined data from the two datasets collected.
  
  
  CONCLUSIONS
  It is possible to determine an ideal trajectory through the C2 pedicle. These measurements may facilitate C2 pedicle screw fixation decreasing the risk of injury to the vertebral artery, spinal cord, or nerve roots. Delineating the individual anatomy in each case with imaging before surgery is recommended.
authors.affiliation: Charles E. Schmidt College of Medicine at Florida Atlantic University and LESS (LESSurgeons) Institute, Division LESSpine Institute, 1100 W. Oakland Park Blvd., Suite #3, Fort Lauderdale, FL 33311, USA. Electronic address: kingsleychin@gmail.com.
authors.forename: Kingsley R
authors.initials: KR
authors.lastname: Chin
authors.affiliation: Department of Orthopedic Surgery, Howard University Hospital, Washington, DC, USA.
authors.forename: Michael V
authors.initials: MV
authors.lastname: Mills
authors.affiliation: LESS (LESSurgeons) Institute, Division, LESSpine Institute, 1100 W. Oakland Park Blvd., Suite #3, Fort Lauderdale, FL 33311, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Seale
authors.affiliation: Less Exposure Surgery (LES) Society, 300 E. Oakland Park Blvd., Suite 502, Fort Lauderdale, FL 33334, USA.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Cumming
mesh_terms: D000328:Adult; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D012306:Risk; D013123:Spinal Fusion / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014711:Vertebral Artery / Q000293:injuries*
keywords: 3D; C2; Cervical; Pedicle screw; Posterior cervical; Trajectory; Vertebral artery injury