title: Accuracy of C2 pedicle screw placement using the anatomic freehand technique.
abstract: OBJECTIVE
  The objective of this study is to evaluate the incidence and prognostic factors of breach rates following the placement of C2 pedicle screws using the anatomic, freehand technique.
  
  
  METHODS
  We retrospectively reviewed the medical records of all patients who underwent C2 transpedicular instrumentation over six years at a single institution. All intraoperative, image-guided techniques were excluded. Breaches were ascertained from immediate postoperative CT images. All images were analyzed by three independent reviewers. The screw length was correlated with (1) the breach rate and (2) the breach severity. Severity of the breached screws reflects the screw circumference (0-360°) perforating the pedicle wall (Grade 1-Grade 4).
  
  
  RESULTS
  Of the 341 C2 pedicle screws inserted in 181 patients, the average screw length was 22.93±3.7mm. The average distance from the foramen transversarium to the screw insertion point was 13.17±2.63mm. The distance from the medial rim of the pedicle to the dura of spinal cord was 3.53±1.57mm. Of the 341 screws, the overall breach rate was 17.3% (n=59). Of the 59 breaches, 89.83% of screws (n=53) breaching the spinal canal was statistically significantly higher than the 10.17% of screws (n=6) breaching the foramen transversarium (p<0.001). Moreover, 27 (45.8%) were Grade 1, 16 (27.1%) Grade 2, 6 (10.2%) Grade 3, and 10 (16.9%) Grade 4. None of the C2 breaches resulted in neurological sequela. No association was found between breach rate and gender, race or age. While the average screw length was 22.93±3.7mm [12-34mm], screw length did not predict a cortical violation (p=0.4) or severity of the breach (p=0.42) in a multiple regression model.
  
  
  CONCLUSIONS
  In this cohort study on the anatomic freehand placement of C2 pedicle screws, the breach rate was 17.3%. Lateral breaches were more common than medial breaches. Screw length was not statistically correlated with cortical violation or severity of breach. Therefore, screw length is not a prognostic factor for C2 pedicle screw misplacement.
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA; Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA. Electronic address: mbydon1@jhmi.edu.
authors: Mohamad
authors: M
authors: Bydon
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA; Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA.
authors: Dimitrios
authors: D
authors: Mathios
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA; Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA.
authors: Mohamed
authors: M
authors: Macki
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA; Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA.
authors: Rafael
authors: R
authors: De la Garza-Ramos
authors: Department of Neuroradiology, Johns Hopkins University School of Medicine, Baltimore, USA.
authors: Nafi
authors: N
authors: Aygun
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA.
authors: Daniel M
authors: DM
authors: Sciubba
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA.
authors: Timothy F
authors: TF
authors: Witham
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA; Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA.
authors: Ziya L
authors: ZL
authors: Gokaslan
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA; Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA. Electronic address: abydon1@jhmi.edu.
authors: Ali
authors: A
authors: Bydon
authors: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA.
authors: Jean-Paul
authors: JP
authors: Wolinksy
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000473:pathology / Q000601:surgery*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D019651:Plastic Surgery Procedures; D012189:Retrospective Studies; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion / Q000379:methods
keywords: C2; Cervical; Freehand; Pedicle; Screws