Clivo-axial angle

The clivo-axial angle (CXA), also known as the clivus canal angle, the clivus vertebral angle, the clivus spinal angle or the clivus cervical angle, indicates the angle between the clivus and the spine. It is used to aid in the diagnosis of craniocervical instability.

Botelho and Ferreira (2013) define the CXA as "The angle between the line extending from the top of the dorsum sellae to the basion and the line between the inferodorsal portions of C2 to the most superodorsal part of the dens."

Several studies have show that a CXA lower than 135 degrees is uncommon in the healthy population (see table below) and is associated with pathological conditions such as brainstem compression in patients with rheumatoid arthritis. A consensus statement formed at the second International CSF Dynamics Symposium of the Chiari and Syringomyelia Foundation in 2013, proposed that a CXA lower than 135 degrees could be seen as potentially pathological.