Basion-axial interval

Dr Owen Kang and Dr Craig Hacking et al.

The basion-axial interval (BAI), as the name suggests, is the horizontal distance between the basion and the posterior cortex of the axis, used in the diagnosis of atlanto-occipital dissociation injuries.

It is the distance (in mm) between the basion and the superior extension of the posterior cortical margin of the body of the axis in the median (midsagittal) plane.

Normal values are <12 mm on plain radiographs and were not found to be reliable of on CT 1 where they range from -8.7 mm to +26 mm in normal subjects.

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Article information

rID: 40482
Section: Gamuts
Synonyms or Alternate Spellings:
  • BAI
  • Basion-axial interval (BAI)

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Cases and figures

  • Base of skull lines (annotated images)
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