TABLE 1.
Description of the quantitative imaging measurements of the craniovertebral junction
| Imaging measurements | Description |
|---|---|
| Angle of head position | Formed by the intersection of a line drawn between the tuberculum sellae and the basion and a second line between the cranio‐ and caudodorsal borders of the axis vertebral body |
| Clivus canal angle | Formed by the line extending from the top of the tuberculum sellae to the basion and the line parallel to the floor of the axis vertebral canal |
| C1‐C2 overlap | Cranial aspect of the axis spinous process to the caudal border of the atlas dorsal arch. A negative value indicates that the axis spinous process is no longer superimposed with the atlas arch. |
| Basion‐dens interval | Basion to the tip of the dens axis |
| Ventral compression index (VCI) | Calculated by dividing the ventral atlantodental interval (VADI) by the dorsal atlantodental interval (DADI), Figure 2. |
| Atlantoaxial distance | Caudal aspect of the atlas dorsal arch to the cranial aspect of the axis lamina |
| Power ratio | Calculated by dividing the distance between the basion and the midpoint of the atlas dorsal arch by the distance from the opisthion to the midpoint of the dorsal aspect of the atlas ventral arch |
| C1‐C2 angle | Formed by the intersection of a line parallel to the atlas dorsal arch and the axis lamina |
| Dens‐to‐axis length ratio (DALR) | Calculated by dividing the length of the dens by the one of the axis body. The length of the dens axis is defined as the distance between the tip and the ventral base of the dens. The length of the axis body is measured from the line drawn perpendicular to the axis body and passing through the base of the dens axis (white dashed line) to the caudal aspect of the axis vertebral body. |
| Cranial translation ratio (CTR) | Calculated by dividing the distance of cranial translation by the length of the dens axis (Figure 3). |
Abbreviations: CTR, cranial translation ratio; DALR, dens‐to‐axis length ratio; DADI, dorsal atlantodental interval; VADI, ventral atlantodental interval; VCI, ventral compression index.