title: Normative data on axial rotation of atlanto-occipital joint on 3 Tesla MRI using a simple and reliable method of calculation.
abstract: BACKGROUND
  Various methods have been used to image and measure the normal range of axial rotation of the atlanto-occipital joint (AOJ), but a simple, precise, and reliable method is needed for everyday practice.
  
  
  OBJECTIVE
  To generate normative ranges for AOJ rotation in various in-vivo positions and to investigate the reliability of a simple imaging method for measurement using routine high-field magnetic resonance imaging (MRI).
  
  
  METHODS
  One hundred healthy volunteers were imaged on 3 T MRI with the AOJ in the center of the field of view. The scans were uniformly performed in seven different positions. The range of axial rotation was calculated by the angle between the craniofacial midline and the line linking the anterior and posterior tubercles of the atlas. The angle was defined as positive when it was angled right, and negative when it was angled left. The actual normative range of axial rotation was the difference between the angle in the supine neutral position and in the other positions.
  
  
  RESULTS
  The normative axial rotation range of the AOJ in different positions was between -4.8° and +5.0°. The mean values of the actual rotation angles in the right supine position with maximum bending, the right supine position maximum rotation, and the right prostrate position maximum rotation were 0.1°, 1.70°, and 0.8°, respectively. The mean values of actual rotation angles in the left supine position with maximum bending, the left supine position with maximum rotation, and the left prostrate positive with maximum rotation were 0.1°, -1.7°, and -1.1°, respectively. The inter-observer reliability tested.
  
  
  CONCLUSIONS
  A simple and reliable method of measurement on 3.0 T MRI demonstrated the normative axial rotation range of the AOJ in different positions to be between -4.8° and +5.0° and it was different from zero in neutral rotation. This method could be practically used to precisely diagnose AOJ rotary subluxation or dislocation.
authors.affiliation: Shandong Medical Imaging Research Institute, Jinan, PR China.
authors.forename: Kai
authors.initials: K
authors.lastname: Liu
authors.forename: Xuecai
authors.initials: X
authors.lastname: Niu
authors.forename: Chunyan
authors.initials: C
authors.lastname: Wu
authors.forename: Lingfei
authors.initials: L
authors.lastname: Guo
authors.forename: Cheng
authors.initials: C
authors.lastname: Liu
authors.forename: Huixiao
authors.initials: H
authors.lastname: Song
authors.forename: Avneesh
authors.initials: A
authors.lastname: Chhabra
mesh_terms: D001269:Atlanto-Occipital Joint / Q000502:physiology*; D006801:Humans; D004204:Joint Dislocations / Q000175:diagnosis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology; D012016:Reference Values; D015203:Reproducibility of Results; D012399:Rotation; D016683:Supine Position
keywords: Atlanto-occipital joint; magnetic resonance imaging; normative; subluxation