title: Preoperative radiographic factors and surgeon experience are associated with cortical breach of C2 pedicle screws.
abstract: METHODS
  A retrospective review study.
  
  
  OBJECTIVE
  In this study, we attempt to identify radiographic variables associated with likelihood of intraoperative breach during C2 pedicle screw placement. In addition, we attempt to correlate surgeon experience with breach rate.
  
  
  BACKGROUND
  Pedicle screws have emerged as an effective approach for obtaining fixation of the axis, yet placement of C2 pedicle screws is technically demanding and poses the risk of injury to the vertebral artery. Given the evidence for substantial variation in C2 anatomy, preoperative assessment of computed tomography (CT) scans may indicate, which patients are at increased risk for cortical breach during the pedicle screw placement.
  
  
  METHODS
  A retrospective review of all patients undergoing C2 pedicle screw fixation at a single institution over the last 6 years was conducted. Radiographic cortical breaches were defined on postoperative CT scans as visualization of the screw beyond the cortical edge. Radiographic measurements were determined from preoperative CT scans and were then correlated with breaches via Student t test. The association of breach rate with surgeon experience was evaluated using univariate linear regression.
  
  
  RESULTS
  Ninety-three patients underwent placement of 170 screws. Cortical breach was detected on postoperative CT scans in 43 screws (25.3%). One clinically significant breach occurred with damage to the left vertebral artery intraoperatively. On axial CT sections, mean pedicle isthmus diameter was significantly smaller in patients with breach than in patients without breach for both left and right sides, P=0.006 and P=0.010, respectively. Specifically, a diameter of less than 6 mm was associated with a nearly 2-fold increase in risk of cortical breach (37% vs. 21%). Surgeons with greater experience in placing C2 pedicle screws were noted to have a lower breach incidence (P=0.004).
  
  
  CONCLUSIONS
  During placement of C2 pedicle screws, likelihood of cortical breach may be associated with size of pedicle and surgeon experience. Extensive preoperative evaluation of CT scans and consideration of technical demands of procedure may help avoid complications with such internal fixation.
authors.affiliation: Department of Neurosurgery, Johns Hopkins School of Medicine, Baltimore, MD, USA.
authors.forename: Hassan
authors.initials: H
authors.lastname: Alosh
authors.forename: Scott L
authors.initials: SL
authors.lastname: Parker
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McGirt
authors.forename: Ziya L
authors.initials: ZL
authors.lastname: Gokaslan
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Witham
authors.forename: Ali
authors.initials: A
authors.lastname: Bydon
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Wolinsky
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sciubba
mesh_terms: D000328:Adult; D000368:Aged; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000601:surgery*; D001863:Bone Screws / Q000009:adverse effects*; D015984:Causality; D002983:Clinical Competence / Q000592:standards / Q000706:statistics & numerical data; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D011300:Preoperative Care / Q000379:methods / Q000592:standards; D012189:Retrospective Studies; D013119:Spinal Cord Injuries / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D013123:Spinal Fusion / Q000009:adverse effects* / Q000193:education / Q000295:instrumentation*; D013663:Teaching; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000592:standards; D014711:Vertebral Artery / Q000000981:diagnostic imaging / Q000293:injuries / Q000601:surgery