Atlantodental interval

Last revised by Ryan Thibodeau on 11 Oct 2023

The atlantodental interval is used in the diagnosis of atlanto-occipital dissociation injuries and injuries of the atlas and axis.

The anterior atlantodental interval is the horizontal distance between the posterior cortex of the anterior arch of the atlas (C1) and the anterior cortex of the dens in the median (midsagittal) plane 2.

The lateral atlantodental interval is the horizontal distance between the lateral cortex of the dens and the medial cortex of the lateral masses of the atlas. The normal value is 3.4 mm in either right or left atlantodental interval. However, normal asymmetry between right and left atlantodental interval can vary up to 0.76 mm. Therefore, asymmetry in lateral atlantodental interval is not a sensitive or specific sign of atlanto-occipital dissociation injuries 2.

Normal values for anterior atlantodental interval are:

  • radiographs

    • adults

      • males: <3 mm

      • females: <2.5 mm 1 (although some authors do not specifically differentiate from males)

    • children: <5 mm 4-7

  • CT

    • adults: <2 mm 1

    • children: <2.6 mm 5

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