Atlantoaxial Instability

Ovid: 5-Minute Sports Medicine Consult, The

Atlantoaxial Instability
Rebecca L. Carl
  • 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 C1–2 joint leading to atlantoaxial instability.
  • Many patients who meet the radiographic definition of AAI are asymptomatic and at low risk for neurological 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 over the age of 10 are most likely to have progression of AAI.
Risk Factors
  • 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.
Lateral cervical radiographs with flexion and extension views are used for screening. AAI is defined radiographically as an increased distance between the odontoid process and the anterior arch of the axis.
  • Obtaining screening x-rays for AAI in asymptomatic patients with Down syndrome is controversial.
    • Because of poor radiographic reproducibility and because many radiographic signs of AAI often resolve over time in asymptomatic patients, the American Academy of Pediatrics retired a position statement that had previously endorsed routine screening.
    • The Special Olympics continues to require radiographic screening in all athletes with Down syndrome.
    • Some suggest screening lateral x-rays in patients with Down syndrome during periods of rapid growth at ages 5, 12, and 18.
  • Most individuals with AAI are asymptomatic.
  • AAI can be acute or chronic. However, acute AAI without a history of preceding symptoms is rare.
    • Patients with acute AAI often present after injury. Injury can be due to direct or indirect trauma. Mechanisms of injury include hyperextension, hyperflexion, direct loading.
    • In patients who have an acute worsening of AAI, participation in organized sports is an uncommon triggering event.
    • Patients with chronic AAI often present with gait changes, progressive weakness, and fatigue. Neck pain, bowel and bladder incontinence, ataxia, spasticity, and quadriplegia can be present with longstanding, severe chronic AAI.
Physical Exam
  • Hyperreflexia
  • Sensory changes
  • Weakness
  • Gait changes
  • Cervical spine range of motion is often normal
Diagnostic Tests & Interpretation
  • Lateral neck radiographs with flexion/extension views:
    • AAI is defined as a space of 5 mm or more between the odontoid process of the axis and the anterior arch of the atlas.
  • Further evaluation with CT or MRI in cervical flexion and extension is often needed to assess for spinal cord compression in patients with AAI on plain radiographs.
Differential Diagnosis
  • Neck sprain/strain
  • Cervical disc herniation
  • Torticollis
  • Vertebral fracture
  • Ligamentous laxity
  • Spinal contusion
  • Epidural hemorrhage


Ongoing Care
Long-term management:
  • Individuals who exhibit signs and symptoms should be restricted from contact sports and other activities that place stress on the neck.
  • Restriction of asymptomatic patients with only radiographic evidence of AAI is somewhat controversial, particularly for noncontact activities:
    • Special Olympics requires that patients with radiographic evidence of atlantoaxial instability be temporarily restricted from the following:
      • Butterfly stroke
      • Diving (including diving starts in swimming)
      • Pentathlon
      • High jump
      • Squat lifts
      • Equestrian sports
      • Artistic gymnastics
      • Soccer
      • Skiing
    • These restrictions can be removed if an asymptomatic athlete (or the athlete's parents in the case of a minor) signs a waiver after having the risks of AAI explained by 2 physicians.
Follow-Up Recommendations
Primary care physicians should counsel families of patients with Down syndrome, rheumatoid arthritis, juvenile inflammatory arthritis, and skeletal dysplasias about possible signs and symptoms of atlantoaxial instability.
Additional Reading
Atlantoaxial instability in Down syndrome: subject review. American Academy of Pediatrics Committee on Sports Medicine and Fitness. Pediatrics. 1995;96:151–154.
Cremers MJ, Bol E, de Roos F, et al. Risk of sports activities in children with Down's syndrome and atlantoaxial instability. Lancet. 1993;342:511–514.
Laiho K, Savolainen A, Kautiainen H, et al. The cervical spine in juvenile chronic arthritis. Spine J. 2002;2:89–94.
Torg JS, Ramsey Emrhein JA. Suggested management guidelines for participation in collision activities with congenital, developmental, or postinjury lesions involving the cervical spine. Med Sci Sports Exerc. 1997;29:S256–S272.
Wills BP, Dormans JP. Nontraumatic upper cervical spine instability in children. J Am Acad Orthop Surg. 2006;14:233–245.
Winell J, Burke SW. Sports participation of children with Down syndrome. Orthop Clin North Am. 2003;34:439–443.
718.88 Other joint derangement, not elsewhere classified, involving other specified sites

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