title: Clinical and computed tomographic evaluation of safety and efficacy of facet screw fixation in the subaxial cervical spine.
abstract: METHODS
  A retrospective study comparing screw positioning and associated complications between 2 different facet screw placement methods.
  
  
  OBJECTIVE
  To review the anatomic location, clinical safety, efficacy, and limitations of 2 facet screw placement techniques.
  
  
  BACKGROUND
  Facet screw fixation in the subaxial cervical spine penetrates 4 cortical layers and affords better stability than lateral mass screws. Takayasu and colleagues recommended placing screws in the sagittal plane. We modified the trajectory to direct the screws laterally from the sagittal plane to place the root at less risk and improve fixation by increasing the excursion of the screws into bone. No clinical reports exist describing the quadricortical facet screw placed in a lateral direction.
  
  
  METHODS
  A total of 95 screws were used in 18 consecutive patients who underwent posterior cervical stabilization for various spinal disorders: 34 screws used sagittal plane screw placement and 61 used our technique. Screw-related complications were reviewed. Screw trajectories and screw tip positions related to the ventral cortical margin and vertebral artery were evaluated using postoperative 3-dimensional computed tomograms taken within 6 months after surgery. Instrumentation failures were evaluated from postoperative 3-dimensional computed tomograms taken 2 years after surgery.
  
  
  RESULTS
  There was 1 complication, nerve root irritation due to screw malposition. Postoperative computed tomographic images revealed that drilling was 30 degrees lateral from the sagittal plane in our method. Fourth cortex penetration failed in 29% of the screws placed in the sagittal plane and in 5% by our method. Screw loosening was significantly increased using screws placed in the sagittal plane (24% vs. 2%).
  
  
  CONCLUSIONS
  Quadricortical facet screw placement aimed at the juncture between the transverse process and the facet is practicable. Screw loosening was significantly reduced using this lateral screw direction. One of the disadvantages of this technique is that extensive cranial exposure is required to align the instruments in the proper sagittal trajectory.
authors.affiliation: Department of Orthopaedic Surgery, Yokohama City University Hospital, Yokohama City, Kanagawa Prefecture, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Aota
authors.forename: Atsushi
authors.initials: A
authors.lastname: Honda
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Saito
mesh_terms: D000368:Aged; D001863:Bone Screws / Q000009:adverse effects; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery*; D005260:Female; D005593:Fracture Fixation, Internal / Q000009:adverse effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D011182:Postoperative Care; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000209:etiology; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D021801:Zygapophyseal Joint / Q000000981:diagnostic imaging* / Q000601:surgery*