We need you! See something you could improve? Make an edit and help improve WikSM for everyone.

Atlantoaxial Instability

From WikiSM
Jump to: navigation, search

Other Names

  • AAI
  • AA Instability
  • Craniovertebral instability
  • Atlantoaxial subluxation
  • Grisel syndrome


  • This page describes instability of the atlantoaxial joint or atlantoaxial instability (AAI)



  • Rare disease, no good data regarding incidence and prevalence across the general population
  • Although only 1% of patients with down syndrome have symptomatic AAI, it is radiographically evidence in up to 30% of patients[1]
  • Prevalence in rheumatoid arthritis estimated to be between 25 and 80%[2]


  • Characterized by excessive movement between C1 and C2 as a result of either bony or ligamentous abnormality
  • Excessive motion can occur between anterior arch of C1 and odontoid process of C2
  • Can also occur between the posterior elements of the facet joints
  • Transverse ligament laxity is most commonly implicated


  • Inflammatory
    • Most common is Rheumatoid Arthritis
    • Due to chronic inflammation, laxity and stretching of the transverse ligament
    • Development of granulation tissue
    • Erosion of bony structures
  • Congenital
  • Traumatic
    • Rare


  • Atlantoaxial joint
    • Consists of C1 (Atlas) and C2 (Axis)
  • Function
    • Support occiput
    • Provides greatest range of motion and flexibility of neck
    • 50% rotation of the cervical spine
    • Most mobile joint in the body
  • Ligaments
    • Cruciate ligament
    • Alar ligaments
    • Apical ligaments
    • Anterior longitudinal ligament (ALL)
    • Transverse ligament

Associated Injuries

Risk Factors

  • Achondroplasia
  • Congenital scoliosis
  • Down Syndrome
  • Morquio syndrome
  • Neurofibromatosis
  • Osteogenesis imperfecta
  • Rheumatoid Arthritis
  • Jeuvenile Rheumatoid Arthritis (JRA)
  • Larsen syndrome
  • Spondyloepiphyseal Dysplasia (SED)
  • Chondrodysplasia Punctata
  • Metatropic Dysplasia
  • Kniest syndrome

Differential Diagnosis

Clinical Features


  • Generally insidious onset with no trauma
  • Patients may report mild neck pain
  • They may also report parasthesia, weakness, myelopathy

Physical Exam: Physical Exam Neck

  • Clinically, they may also have neuro deficits on exam
  • Rarely they have profound neurological deficits
  • Including hyperreflexia, muscle weakness, broad based gait, loss of motor, bladder dysfunction

Special Tests



  • Standard cervical spine radiographs
  • Findings
    • Sum of C1 on C2 lateral mass is greater than 7 mm
    • Atlantodens interval (ADI) > 3 mm (adults) or > 4.5-5 mm (children) is abnormal
    • space-available-cord (SAC) = posterior atlanto-dens-interval (PADI) < 14 mm
  • Consider dynamic flexion-extension films


  • May help better evaluate osseous lesions, especially in the setting of trauma


  • May better help evaluate soft tissue lesions


Fielding and Hawkins Classification

  • Type I - Simple rotatory displacement with an intact transverse ligament[3]
  • Type II - Anterior displacement of C1 on C2 of 3 to 5 mm with one lateral mass serving as a pivot point and a deficiency of the transverse ligament
  • Type III - Anterior displacement exceeding 5 mm
  • Type IV - Posterior displacement of C1 on C2



  • Prognosis is good for patients who undergo spinal fusion (need citation)
    • Most patients with successful surgery have good functional recovery


  • Down Syndrome
    • Children with down syndrome should be screened at age 5, and perhaps in again in adulthood (need citation)
  • Type I
  • Type II
    • If symptomatic, neurosurgery should be involved


  • Type III
    • Unstable, requires surgical management
  • Type IV
    • Unstable, requires surgical management
  • Technique
    • Transarticular screws
    • Screw-rod construct
    • Sublaminar wiring
    • Halifax clamp

Rehab and Return to Play


  • Needs to be updated

Return to Play

  • Special Olympics criteria for athletes with Down Syndrome (need citation)
    • All children with Down syndrome must undergo radiographic and neurologic examinations to exclude AAI.
    • IF AAI detected, restricted from gymnastics, diving, pentathlon, butterfly stroke, diving starts in swimming, high jump, soccer, and certain warmup exercises
  • Individuals should undergo long term monitoring


  • Neck pain
  • Myelopathy
  • Spasticity
  • Radicular symptoms

See Also


  1. Pueschel, Siegfried M., and Francis H. Scola. "Atlantoaxial instability in individuals with Down syndrome: epidemiologic, radiographic, and clinical studies." Pediatrics 80.4 (1987): 555-560.
  2. Zikou, Anastasia K., et al. "Radiological cervical spine involvement in patients with rheumatoid arthritis: a cross sectional study." The Journal of rheumatology 32.5 (2005): 801-806.
  3. Fielding, J. WILLIAM, and R. J. Hawkins. "Atlanto-axial rotatory fixation.(Fixed rotatory subluxation of the atlanto-axial joint)." The Journal of bone and joint surgery. American volume 59.1 (1977): 37-44.
Created by:
John Kiel on 17 April 2020 19:45:05
Last edited:
25 May 2023 06:45:10