title: A New Method of Measuring the Occipitocervical Angle That Could be Applied as an Intraoperative Indicator During Occipitocervical Fusion.
abstract: METHODS
  A method for measuring occipitocervical angle.
  
  
  OBJECTIVE
  To develop a new method of measurement for assessing the occipitocervical angle using intraoperative fluoroscopic imaging, and to examine its reliability.
  
  
  BACKGROUND
  To avoid postoperative complications following occipitocervical fusion, it is vital to obtain a suitable fusion angle between the occipital bone and the upper cervical spine.
  
  
  METHODS
  The subjects were 30 cases with occipito-atlanto-axial lesions and 30 healthy volunteers. Lateral plain radiographs of the cervical spine in neutral position were used to draw the McGregor line, the line between the external occipital protuberance and the most caudal point on the midline occipital curve (Oc line), the tangential line of the inferior endplate of the C2 vertebra (C2 line), and the posterior longitudinal line of the C2 vertebra (Ax line). The angles formed by these 4 lines and the horizontal line were measured. The O-C2 angle and the Oc-Ax angle, the new indicator, were measured by 3 doctors and reliability was evaluated.
  
  
  RESULTS
  In the disease group, mean intraobserver variances of the McGregor, Oc, C2, Ax, O-C2, and Oc-Ax angles were 0.7, 1.3, 1.5, 1.2, 1.6, and 1.9 degrees. Mean intraobserver intraclass correlation coefficients were 0.997, 0.994, 0.994, 0.997, 0.989, and 0.988, showing high intraobserver reliability for all angles. Mean interobserver intraclass correlation coefficients were 0.998, 0.996, 0.994, 0.997, 0.988, and 0.990, showing high interobserver reliability for all angles. The same reliability was obtained in the healthy group.
  
  
  CONCLUSIONS
  The Oc-Ax angle is as reliable an indicator as the conventional O-C2 angle, and could be used as a new intraoperative indicator for occipitocervical fusion. It may be particularly useful in cases where it is difficult to identify the McGregor line and/or the inferior endplate of the C2 vertebra.
  
  
  METHODS
  Level 3-diagnostic study.
authors.affiliation: *Department of Orthopaedics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine †Department of Orthopaedics, Tanabe Central Hospital ‡Department of Rehabilitation Medicine, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Nagashima
authors.forename: Masateru
authors.initials: M
authors.lastname: Nagae
authors.forename: Yuji
authors.initials: Y
authors.lastname: Arai
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tonomura
authors.forename: Ryota
authors.initials: R
authors.lastname: Takatori
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Sukenari
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Fujiwara
authors.forename: Koshiro
authors.initials: K
authors.lastname: Sawada
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Mikami
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Kubo
mesh_terms: D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D002574:Cervical Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D002648:Child; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D007430:Intraoperative Care / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009777:Occipital Bone / Q000503:physiopathology* / Q000601:surgery*; D013123:Spinal Fusion