One-third of patients with anterior Atlanto-axial subluxation have a neurologic deficit or die.
Subluxation may be due to:
1. disruption (rupture) of the transverse atlantal ligament (TAL): the atlantodental interval (ADI) will be increased
a) attachment points of the TAL may be weakened in rheumatoid arthritis
b) trauma: may cause anatomic or functional ligament disruption
2. incompetence of the odontoid process: ADI will be normal
b) congenital hypoplasia,e.g.Morquio syndrome