etiology The atlantoaxial joint is an important "transitional zone" in the cervical spine prone to instability by both degenerative and traumatic processes Pathophysiology adult causes degenerative login to view 3 more bullets traumatic login to view 3 more bullets pediatric causes degenerative login to view 3 more bullets trauma/infection login to view 1 more bullet Anatomy Osteology bony articulations C1-2 facet joints Ligaments transverse apical alar ligament complex transverse ligament login to view 1 more bullet apical ligament login to view 1 more bullet alar ligaments login to view 1 more bullet Biomechanics the atlantoaxial joint provides ~50% of rotation in the cervical spine this is enabled by the peg (C2) in ring (C1) anatomy Physical Exam Symptoms neck pain neurologic symptoms Physical exam neurologic deficits often appear late in disease process due to capacious nature of spinal canal at the C1 level myelopathic symptoms login to view 6 more bullets Imaging Radiographs flexion-extension views atlantodens interval (ADI) login to view 7 more bullets space available for the cord (SAC) = posterior atlantodens interval (PADI) login to view 4 more bullets open mouth odontoid sum of lateral mass displacement login to view 7 more bullets Treatment Determined by specific condition adult atlantoaxial instability Down syndrome rheumatoid arthritis os odontoideum odontoid fracture atlas fractures transverse ligament injuries pediatric atlantoaxial instability JRA Morquio syndrome rotatory atlantoaxial subluxation