title: Fluoroscopically guided anterior atlantoaxial transarticular screws: a feasibility and trajectory study using CT-based simulation software.
abstract: BACKGROUND
  Anterior transarticular screw (ATAS) fixation has been suggested as a viable alternative to posterior stabilization. However, we are not aware of previous reports attempting to establish the usefulness of specific fluoroscopic landmark-guided trajectories in the use of ATAS, and we could find no reference to it in a computerized search using MEDLINE.
  
  
  OBJECTIVE
  To determine the anatomic feasibility of ATAS placement using defined fluoroscopic landmarks to guide screw trajectory.
  
  
  METHODS
  Evaluation using three-dimensional screw insertion simulation software and 1.0-mm-interval computed tomographic scans.
  
  
  METHODS
  Computed tomographic scans of 100 patients including 50 men and 50 women.
  
  
  METHODS
  Incidence of violation of the vertebral artery groove of C1 and C2, the spinal canal, and the atlanto-occipital joint and screw lengths and lengths of C1 and C2 purchase.
  
  
  METHODS
  Four screw trajectories were determined: promontory screw (PS), single central facet (CF) screw, and medial (MF) and lateral (LF) double facet screws. Placement of a 4.0-mm screw was simulated using defined fluoroscopic landmarks for each trajectory. The previously mentioned outcome measures were evaluated and compared for the four trajectories. This study was not supported by any financial sources, and there is no topic-specific potential conflict of interest with this study.
  
  
  RESULTS
  No violation of the C1 or C2 vertebral artery groove or of the spinal canal was observed for any of the screw types. Screw lengths and the length of C2 purchase were by far the longest for PS (40.4±2.8 and 25.7±2.1 mm, respectively; p<.001 in all post hoc comparisons). The length of C1 purchase was longer for CF (16.4±2.3 mm) and LF (15.8±1.6 mm) than PS (14.7±2.0 mm) and MF (14.6±2.4 mm) (p≤.001, respectively). There was no atlanto-occipital joint violation if the length of C1 purchase was set at 12 mm for CF and LF and at 10 mm for PS and MF.
  
  
  CONCLUSIONS
  Our results suggest that it may be possible to place ATASs without violating the vertebral artery groove, spinal canal, or the atlanto-occipital joint by using the described entry points, trajectories, and fluoroscopic landmarks.
authors.affiliation: Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, 166 Gumiro, Bundang-ku, Sungnam 463-707, Republic of Korea.
authors.forename: Mary R A
authors.initials: MR
authors.lastname: Padua
authors.forename: Jin S
authors.initials: JS
authors.lastname: Yeom
authors.forename: So Y
authors.initials: SY
authors.lastname: Lee
authors.forename: So M
authors.initials: SM
authors.lastname: Lee
authors.forename: Ho-Joong
authors.initials: HJ
authors.lastname: Kim
authors.forename: Bong-Soon
authors.initials: BS
authors.lastname: Chang
authors.forename: Choon-Ki
authors.initials: CK
authors.lastname: Lee
authors.forename: K Daniel
authors.initials: KD
authors.lastname: Riew
mesh_terms: D000328:Adult; D000368:Aged; D001269:Atlanto-Occipital Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D001863:Bone Screws; D003198:Computer Simulation; D005260:Female; D005471:Fluoroscopy / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012984:Software; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D016896:Treatment Outcome
keywords: Anterior atlantoaxial transarticular screws; Atlantoaxial fixation; Screw fixation; Vertebral artery injury; atlanto-occipital joint violation