Condylar-C1 Interval
The Condylar-C1 Interval measures the distance between each occipital condyle (the rounded bony knobs at the base of the skull) and the matching joint surface on C1 (atlas). It helps detect instability where the skull may move abnormally on the top vertebra. It is an important finding after trauma, connective-tissue disorders, or when joint degeneration occurs.
The Condylar-C1 Interval measurement helps assess for craniocervical instability (CCI), specifically atlanto-occipital instability or injury, and is best evaluated on high-resolution CT or Cone Beam CT Scans with less than 1 mm thickness.
Normal measurement at each joint is less than 1.5 mm, whereas abnormal measurement is greater than 1.5 mm or there is asymmetry between left and right sides, or the sum of left and right is greater than 3.0 mm and is strongly suggestive of atlanto-occipital instability or injury.
If the Condylar-C1 Interval is greater than 1.5 mm, or if the condylar sum is greater than 3 mm, or any abnormalities such as joint degeneration or gaps on dynamic imaging is found, a neurosurgical consultation is recommended.