Atlantoaxial Instability (AAI)


Rheumatologic Disease

  • Ankylosing Spondylitis (see Ankylosing Spondylitis, [[Ankylosing Spondylitis]])
  • Enteropathic Arthritis
  • Psoriatic Arthritis (see Psoriasis, [[Psoriasis]])
  • Reiter’s Syndrome (see Reiters Syndrome, [[Reiters Syndrome]])
  • Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis, [[Rheumatoid Arthritis]]): due to transverse ligament inflammation -> predisposes atlantoaxial subluxation
  • Systemic Lupus Erythematosus (SLE) (see Systemic Lupus Erythematosus, [[Systemic Lupus Erythematosus]])


  • Cartilage-Hair Hyperplasia
  • Cerebral Palsy
  • Chondrodysplasia Punctata
  • Congenital Scoliosis
  • Down Syndrome: due to tranverse ligament laxity
  • Dwarfism
  • Head and Neck Infection (especially pharyngeal infection): due to transverse ligament inflammation, predisposing to atlantoaxial subluxation
  • Hypoplasia or Absence of Dens
  • Kniest Syndrome
  • Larsen Syndrome
  • Metatropic Dysplasia
  • Morquio Syndrome
  • Mucopolysaccharidoses
  • Neurofibromatosis (see Neurofibromatosis, [[Neurofibromatosis]])
  • Odontoid Abnormalities
  • Os Odontoideum
  • Ossiculum Terminale
  • Osteogenesis Imperfecta
  • Pseudoachondroplasia
  • Scott Syndrome
  • Spondyloepiphyseal Dysplasia Congenita
  • Steroid Therapy
  • Third Condyle
  • Trauma to Neck
  • Tumors: may cause fracture of body of the axis


Mechanisms of Atlantoaxial Instability

  • Bony Odontoid Abnormalities: may be due to either abnormal odontoid development/ossification or fracture
  • Fracture of Body of the Axis: may occur with tumors
  • Transverse Ligament Laxity/Inflammation: may occur with RA and infections


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