title: Study of the anatomical variations of vertebral artery in C2 vertebra with magnetic resonance imaging and its application in the C1-C2 transarticular screw fixation.
abstract: METHODS
  Use of magnetic resonance imaging (MRI) with Constructive Interference in Steady State (CISS) sequence and isometric voxels to demonstrate the anatomic variations of vertebral artery in C2 vertebra.
  
  
  OBJECTIVE
  To determine the transarticular screw trajectory on CISS MRI and to identify patients with anatomic variations of vertebral artery in C2 vertebra.
  
  
  BACKGROUND
  Atlantoaxial transarticular screw fixation has been reported to be biomechanically superior to other posterior techniques for atlantoaxial arthrodesis. Vertebral artery injury can be associated with catastrophic sequelae. Anatomic variation of vertebral artery is well recognized and computed tomography scan is the traditional preoperative assessment. However, no report has evaluated the use of MRI in preoperative assessment for the screw trajectories and the anatomic variation of vertebral artery.
  
  
  METHODS
  The 3-dimensional (3D) CISS MRI with isometric voxels was performed in 30 local Chinese patients. The 3D reconstruction images were created to determine the proposed screw trajectories and their relationship with the vertebral arteries.
  
  
  RESULTS
  In 12 patients (40%), the vertebral arteries were lying within the screw trajectories prohibiting transarticular screw fixation on at least one side. Bilateral variations with high risk of vertebral artery injuries were found in 6 patients. The remaining 6 patients had unilateral variations prohibiting the insertion of transarticular screws on one side.
  
  
  CONCLUSIONS
  The 3D CISS MRI with isometric voxels is a safe and simple imaging technique to outline the vertebral arteries in C2. Reconstruction images are easily created and undistorted. It is one of the useful imaging in preoperative planning of transarticular screw fixation and determination of anatomy of vertebral artery.
authors.affiliation: Division of Spine Surgery, Department of Orthopaedics and Traumatology, United Christian Hospital, Kwun Tong, Kowloon, Hong Kong. lausw2@ha.org.hk
authors.forename: Sun Wing
authors.initials: SW
authors.lastname: Lau
authors.forename: Lun Kit
authors.initials: LK
authors.lastname: Sun
authors.forename: Raymond
authors.initials: R
authors.lastname: Lai
authors.forename: Man Sze Karen
authors.initials: MS
authors.lastname: Luk
authors.forename: Yuet Sun
authors.initials: YS
authors.lastname: Ng
authors.forename: Nang Man Raymond
authors.initials: NM
authors.lastname: Wong
authors.forename: Pui Yau
authors.initials: PY
authors.lastname: Lau
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology* / Q000601:surgery; D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology* / Q000601:surgery; D001863:Bone Screws; D001270:Cervical Atlas / Q000033:anatomy & histology* / Q000601:surgery; D002648:Child; D005260:Female; D005592:Fracture Fixation / Q000379:methods; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016268:Internal Fixators; D007593:Joint Instability / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D014711:Vertebral Artery / Q000033:anatomy & histology* / Q000601:surgery