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Atlantoaxial Instability

Comprehensive guide to atlantoaxial instability - C1-C2 pathology, Down syndrome association, ADI measurement, surgical stabilization and fusion techniques for orthopaedic exam

πŸ“…Last reviewed: December 2024πŸ₯Bones & Joints

πŸ“–What is Atlantoaxial Instability?

Comprehensive guide to atlantoaxial instability - C1-C2 pathology, Down syndrome association, ADI measurement, surgical stabilization and fusion techniques for orthopaedic exam

πŸ”¬What Causes It?

  • Down syndrome (15-20% have atlantoaxial instability) - lax ligaments due to collagen abnormality
  • Rheumatoid arthritis - inflammation destroys transverse ligament and causes C1-C2 erosion
  • Congenital bone abnormalities - os odontoideum (separate odontoid process), hypoplastic odontoid
  • Trauma - fracture of odontoid (dens) or rupture of transverse ligament
  • Infection - Grisel syndrome (pharyngitis causing inflammatory laxity)
  • Connective tissue disorders - Ehlers-Danlos syndrome, Marfan syndrome (ligament laxity)

⚠️Risk Factors

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You may be at higher risk if:

  • Down syndrome - 15-20% have AAI, 1-2% develop symptomatic spinal cord compression
  • Rheumatoid arthritis - 25-30% have C1-C2 involvement
  • Previous neck trauma or fractures
  • Family history of connective tissue disorders
  • Participation in contact sports or gymnastics (especially with Down syndrome - now contraindicated)

πŸ›‘οΈPrevention

  • βœ“Down syndrome children: Screening cervical spine X-rays at age 3-5 years (before starting contact sports) and repeat at age 12 years - identify AAI before symptoms
  • βœ“STRICT activity restrictions for Down syndrome with AAI: NO contact sports, gymnastics, diving, trampolining, soccer headers (Special Olympics banned list)
  • βœ“Rheumatoid arthritis patients: Aggressive disease control with DMARDs and biologics reduces AAI incidence, cervical spine screening X-rays at diagnosis and every 2-3 years
  • βœ“Connective tissue disorder patients (Ehlers-Danlos, Marfan): Avoid high-impact activities and contact sports, regular cervical spine monitoring
  • βœ“Post-trauma: Prompt assessment and treatment of odontoid fractures or transverse ligament injuries prevents chronic AAI
  • βœ“Grisel syndrome prevention: Early treatment of pharyngitis/tonsillitis in children, awareness of torticollis as red flag (not just 'stiff neck')