Table I.

Types of cervical spine instability

Type of instability
AAS atlanto axial subluxation	instability in atlanto-axial joints due to the weakening of the structure or rupture of ligaments as well as subchondral bone ulceration – anterior – occurring in the anterior median atlanto-axial joint, located between anterior arch of C1 and the dens of the axis – posterior – occurring in the posterior median atlanto-axial joint, located between posterior arch of C1 and the dens of the axis – lateral – asymmetrical or unilateral changes of the lateral atlanto-axial joint leading to impairment in rotation
SAS subaxial subluxation	subluxation occurring in joints on C3–C7 level due to the destruction of articular surface and ligaments between spinous processes
CrS cranial settling	superior migration of the odontoid into foramen magnum