title: Prevalence of High-Riding Vertebral Artery and Morphometry of C2 Pedicles Using a Novel Computed Tomography Reconstruction Technique.
abstract: METHODS
  Cross-sectional, matched-pair comparative study.
  
  
  OBJECTIVE
  To determine whether a thin-sliced pedicular-oriented computed tomography (TPCT) scan reconstructed from an existing conventional computed tomography (CCT) scan is more accurate for identifying vertebral artery groove (VAG) anomalies than CCT.
  
  
  BACKGROUND
  Posterior atlantoaxial transarticular screw fixation and C2 pedicle screws can cause vertebral artery (VA) injury. Two anatomic variations of VAG anomalies are associated with VA injury: a high-riding VA (HRVA) and a narrow pedicle of the C2 vertebra. CCT scan is a reliable method used to evaluate VAG anomalies; however, its accuracy level remains debatable. Literature comparing the prevalence of C2 VAG anomalies between CCT and TPCT is limited.
  
  
  METHODS
  A total of 200 computed tomography scans of the upper cervical spine obtained between January 2008 and December 2011 were evaluated for C2 VAG anomalies (HRVA and narrow pedicular width) using CCT and TPCT. The prevalence of C2 VAG anomalies was compared using these two different measurement methods via a McNemar's test.
  
  
  RESULTS
  Of the 200 patients studied, 23 HRVA (6.01%; 95% confidence interval [CI], 3.61%-8.39%) were detected with CCT, whereas 66 HRVA (16.54%; 95% CI, 12.85%-20.23%) were detected with TPCT (p<0.001). Sixty-two narrow pedicles (15.58%; 95% CI, 11.99%-19.15%) were detected with CCT, whereas 90 narrow pedicles (22.83%; 95% CI, 18.58%-26.87%) were detected with TPCT (p<0.001).
  
  
  CONCLUSIONS
  VAG anomalies are commonly observed. A preoperative evaluation using TPCT reconstructed from an existing CCT revealed a significantly higher prevalence of C2 VAG anomalies than did CCT and showed comparable prevalence to previously published studies using more sophisticated and higher risk techniques. Therefore, we propose TPCT as an alternative preoperative evaluation for C2 screw placement and trajectory planning.
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Wiwat
authors.initials: W
authors.lastname: Wajanavisit
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Thamrong
authors.initials: T
authors.lastname: Lertudomphonwanit
authors.affiliation: Department of Radiology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Praman
authors.initials: P
authors.lastname: Fuangfa
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Pongsthorn
authors.initials: P
authors.lastname: Chanplakorn
authors.affiliation: Department of Orthopedics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Chaiwat
authors.initials: C
authors.lastname: Kraiwattanapong
authors.affiliation: Department of Radiology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Supaneewan
authors.initials: S
authors.lastname: Jaovisidha
keywords: C2 screw; High-riding vertebral artery; Pedicle; Vertebral artery; X-ray computed tomography