title: Anterior occiput-to-axis screw fixation: part I: a case report, description of a new technique, and anatomical feasibility analysis.
abstract: METHODS
  A case report of anterior screw fixation from the axis to the occiput is described, as is the surgical technique. The pertinent anatomy is described with a radiographic assessment of the feasibility, safety, and general applicability of this technique.
  
  
  OBJECTIVE
  To describe a novel technique of anterior occipitocervical fixation and the pertinent anatomy.
  
  
  BACKGROUND
  In unique clinical situations where posterior fixation techniques may not be possible or may have already failed, an anterior screw fixation technique may add stability to further attempts at obtaining a posterior arthrodesis.
  
  
  METHODS
  A case report is presented, followed by a detailed description of the surgical technique. Ten normal cervical spines had radiographs and computed tomography scans with reformats reviewed to determine screw entry points, target points, and proposed screw trajectories. Following screw insertion in eight fresh frozen human cadaver spine specimens, dissection verified screw location relative to structures at risk.
  
  
  RESULTS
  The ideal entry point is located caudal to the C2 superior facet joint in line with the medial third of the C2 superior facet. The screw is directed 25 degrees posteriorly in the sagittal plane and 15 degrees laterally in the coronal plane. The screw tip is located in the posterolateral third of the occipital condyle. Anatomic variation is considerable and makes this technique inadvisable in up to 20% of cases. Structures at risk include the vertebral artery and the hypoglossal nerve.
  
  
  CONCLUSIONS
  This new technique of anterior fixation of the atlas to the occiput is feasible and safe if meticulous surgical planning is performed.
authors.affiliation: Division of Spine, Department of Orthopaedics, University of British Columbia and the Combined Neurosurgical and Orthopaedic Spine Program, Vancouver Hospital and Health Sciences Centre, Canada. mdvorak@vanhosp.bc.ca
authors.forename: Marcel F S
authors.initials: MF
authors.lastname: Dvorak
authors.forename: Charles
authors.initials: C
authors.lastname: Fisher
authors.forename: Mike
authors.initials: M
authors.lastname: Boyd
authors.forename: Mike
authors.initials: M
authors.lastname: Johnson
authors.forename: Rob
authors.initials: R
authors.lastname: Greenhow
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Oxland
mesh_terms: D000063:Accidents, Traffic; D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D005240:Feasibility Studies; D005260:Female; D005471:Fluoroscopy / Q000379:methods; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009777:Occipital Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D010347:Patient Care Planning; D018579:Patient Selection; D012086:Reoperation; D012306:Risk; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*; D013238:Stereotaxic Techniques; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome