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Open Mouth Odontoid

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Open Mouth Odontoid, Odontoid View Cervical Spine XRay

  • See Also
  1. Cervical Spine Imaging in Acute Traumatic Injury
  2. Cross-Table Lateral C-Spine
  3. C-Spine XRay
  4. Cervical Spine XRay in Acute Traumatic Injury
  • Anatomy
  1. Axis (C1)
    1. orthoSpineVertebraeCervical1AtlasGrayBB86.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. Odontoid (C2) Lateral
    1. orthoSpineVertebraeCervical2LateralGrayBB88.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  3. Odontoid (C2) from Above
    1. orthoSpineVertebraeCervical2GrayBB87.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  4. C1 on C2
    1. orthoSpineC1to2XsGrayBB308.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  • Evaluation
  • Adequate film criteria
  1. C1-2 Fractures are very high risk
    1. More common at the extremes of age (very young and old)
  2. Lateral masses of C1 seen
  3. Entire odontoid and the superior aspect of C2 Vertebral body visualized
  4. Foramen magnum view (tip shot)
    1. XRay directed at the C1-2 interface from below the angle of the jaw
    2. Consider if unable to view odontoid tip on standard odontoid view
    3. However, can miss odontoid Fractures due to overlap (Cervical Spine CT is far preferred)
  • Evaluation
  • Alignment
  1. Occipital condyle articulates with C1 lateral masses
  2. C2 Odontoid sits evenly between the C1 lateral masses (atlantodental interval)
    1. Spacing is symmetric to either side of the odontoid
    2. Asymmetry of spacing >1 mm is abnormal
  3. Lateral borders of c1 and c2 Vertebrae should line up
    1. Splaying apart (separation) of the lateral masses is abnormal
      1. Results in the malalignment of the C1 on C2 lateral masses
    2. Vertebral landmarks shifted in on one side
      1. Should be shifted out on other side
  • Evaluation
  • Bony Margins
  1. Odontoid should have uninterrupted cortex to C2
  2. Odontoid view C1 and C2 should line up
  • References
  1. Tubbs and Janicki (2025) Mastering Emergency Imaging, CCME, accessed 8/7/2026