Atlantoaxial Instability

Atlantoaxial Instability

Rebecca L. Carl, MD, MSCI



  • Atlantoaxial instability (AAI) is the term for increased motion at the joint between the 1st and 2nd cervical vertebrae (the atlas and the axis).

  • Congenital, inflammatory, traumatic, or infectious conditions may weaken the structures supporting the C1-C2 joint leading to AAI.

  • Many patients who meet the radiographic definition of AAI are asymptomatic and at low risk for neurologic sequelae.

  • Synonym(s): atlantoaxial subluxation


  • The incidence of radiographic/asymptomatic AAI in individuals with Down syndrome is estimated between 10% and 20%.

  • The incidence of symptomatic AAI is much lower at ˜2.6%.

  • Incidence of AAI increases with age, and progression may occur during growth spurts.

  • For individuals with Down syndrome, males age > 10 yr are most likely to have progression of AAI.


  • Down syndrome

  • Rheumatoid arthritis

  • Juvenile idiopathic arthritis

  • Many forms of dwarfism/skeletal dysplasias

  • Marfan syndrome: increased incidence of C1-C2 hypermobility, but symptoms are rare

Mar 14, 2020 | Posted by in SPORT MEDICINE | Comments Off on Atlantoaxial Instability
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