title: Computer-assisted C1-C2 Transarticular Screw Fixation "Magerl Technique" for Atlantoaxial Instability.
abstract: METHODS
  A retrospective study.
  
  
  OBJECTIVE
  To evaluate the surgical results of computer-assisted C1-C2 transarticular screw fixation for atlantoaxial instability and the usefulness of the navigation system.
  
  
  BACKGROUND
  We used a computed tomography (CT)-based computer navigation system in planning and screw insertion in Magerl's procedure, which provides the most rigid atlantoaxial fusion, to avoid risk of vertebral artery (VA) tear by avoiding high-riding VA during screw insertion.
  
  
  METHODS
  Twenty patients who underwent atlantoaxial fusion under the CT-based navigation system were studied. The mean observation period was 33.5 months. The evaluated items included the existence of VA stenosis by preoperative magnetic resonance angiography, surgical time, blood loss volume, Japanese Orthopaedic Association (JOA) score and Ranawat's pain criteria before surgery and at final follow-up, postoperative screw position evaluated by CT, and bony fusion.
  
  
  RESULTS
  The mean operation time was 205 minutes, with the mean blood loss volume of 242 ml. The mean JOA score was 11.6 points before surgery and 13.7 at final follow-up. Occipital and/or cervical pain presented before operation was remitted or resolved in all patients. Evaluation of screw insertion by CT revealed correct penetration to atlantoaxial joints, with a perforation rate of 2.6%. There was no complication, including VA tear, and all patients who were followed-up during one year or more after surgery achieved bony fusion. Some subjects who appeared inappropriate for surgery from CT images were assessed as eligible for surgery based on the evaluation results obtained using the navigation system.
  
  
  CONCLUSIONS
  It was demonstrated that the CT-based navigation system is an effective support device for Magerl's procedure.
authors.affiliation: Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Uehara
authors.forename: Jun
authors.initials: J
authors.lastname: Takahashi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Hirabayashi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hashidate
authors.forename: Nobuhide
authors.initials: N
authors.lastname: Ogihara
authors.forename: Keijiro
authors.initials: K
authors.lastname: Mukaiyama
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kato