Several indirect measurements on CT can be used to assess ligamentous integrity at the craniocervical junction. The Wackenheim line, a straight line extending along the posterior margin of the clivus through the dens, should not intersect the dens on plain film, with violation of this relationship raising concern for basilar invagination. The basion to axion interval, or BAI, is also used, which is determined by measuring the distance between an imaginary vertical line at the anterior skull base, or basion, at the foramen magnum, and the axis of the cervical spine along its posterior margin, which should measure 12 mm, an assessment more reliable on radiograph than CT. The distance between the atlas and the<unk>  condyles, the<unk><unk>  interval (AOI), should measure less than 4 mm, and is better assessed on coronal images. The distances between the dens and surrounding structures are also key features that can suggest the diagnosis, with the normal distance between the dens and basion (BDI) measuring less than 9 mm on CT, and the distance between the dens and atlas (ADI) measuring less than 3 mm on CT, although this can be increased in cases of rheumatoid arthritis due to pannus formation. Lastly, the<unk><unk>  interval can be measured. The Powers ratio was formerly used, which was the tip of the basion to the spinolaminar line, divided by the distance from the tip of the opisthion to the midpoint of the posterior aspect of the anterior arch of C1. It is no longer recommended due to low sensitivity and difficulty identifying landmarks. It also will miss vertical or posterior displacement of the cervical spine.
Atlanto-occipital dislocation
Zygomaticomaxillary complex fracture
Galeazzi fracture
Olecranon fracture
Cervical dislocation
Crus fracture
Basilar skull fracture
Gosselin fracture