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Atlantoaxial Instability

From WikiSM

Other Names

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

Background

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

History

  • First discussed in the literature in 1830 (need citation)

Epidemiology

  • 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]

Introduction

Illustration of the atlanto axial joint
Schematic representation of atlantoaxial dislocation. Lateral view of the normal cervical spine in relation to the occiput (left) compared with an abnormal relationship between the cervical spine and occiput representing an atlantoaxial dislocation (right). An increase in the distance between the anterior surface of the dens and the posterior surface of the C1 tubercle (A) as measured by the gray arrowed line is shown. The dotted line represents an imaginary line connecting the spinolaminar white lines (the junction between the lamina and the spinous process) and shows that the body of C1 (B) is displaced anteriorly relative to the cervical spine. The atlantodental interval (ADI) is measured between the posterior aspect of the anterior atlas ring and the anterior aspect of the odontoid process. The ADI is often constant in distance during movement of the head and generally does not exceed 3 mm for adults and 5 mm for children. Atlantoaxial dislocation is defined as ADI greater than 3 mm in adults older than 18 years of age and greater than 5 mm in children.[3]

General

  • Characterized by excessive movement between C1 and C2 as a result of either bony or ligamentous abnormality
  • Most commonly due to ligamentous laxity, osseous abnormalities, trauma, or inflammatory processes
  • Diagnosis is based on clinical suspicion and confirmed on imaging, typically dynamic C spine radiographs
  • Management depends on severity, asymptomatic cases can be observed while symptomatic or unstable cases require surgical fixation

Location

  • 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

Etiology

  • 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

Anatomy of the Atlanto Axial Joint

Associated Injuries

Risk Factors

Congenital conditions associated with atlantoaxial dislocation[3]
  • 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

Differential Diagnosis Neck Pain

Clinical Features

The Sharp Purser Test[4]

History

  • Generally insidious onset with no trauma
  • Patients may report mild neck pain, which can be persistent or intermittent
  • Headaches are a less common feature
  • They may also report parasthesia, weakness, myelopathy
  • Family history of trauma or underlying degenerative disease may be contributory

Physical Exam: Physical Exam Neck

  • Limited cervical range of motion in rotation, flexion and extension
  • Torticollis, head tilt, craniocervical kyphosis
  • Prominent tenderness at the occipito-cervical junction, and crepitus
  • 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

Evaluation

Imaging findings consistent with atlantoaxial subluxation and instability. (a) T2-weighted sagittal view of the cervical spine demonstrating sequelae of cord compression just below the level of the foramen magnum. e predental space is markedly increased measuring approximately 1.5 cm. Definite stenosis and cord compression at this level likely attributed to supine position during image acquisition. (b) e cord is flattened and of abnormal signal characteristic at C2 level, where there appears to be an anteriorly displaced os odontoideum. (c) Sagittal bone window of computerized tomography redemonstrating atlantoaxial subluxation and dystopic os odontoideum. Dynamic changes appreciated on plain radiographs in (d) flexion and (e) extension[5]
Neutral (left), extension (center), and flexion (right) lateral X-rays showing the atlantodental interval (ADI) anterior to the odontoid process and the space available for spinal cord posteriorly. The ADI is above the average for adults of 3 mm and is slightly reduced in extension, but severely increased in flexion. This patient's space available for spinal cord (SAC) reducing to below 14 mm indicates risk of paralysis[3]

Radiographs

  • 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

CT

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

MRI

  • May better help evaluate soft tissue lesions

Classification

Wang classification system of atlantoaxial dislocations[3]

Fielding and Hawkins Classification

  • Type I: Simple rotatory displacement with an intact transverse ligament[6]
  • 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

Wang Classification of Atlantoaxial Dislocations

  • Type I
    • Description: Instability
    • Reducible in dynamic X-rays
    • Incidence: 52.2%
    • Surgical technique: posterior fusion
  • Type II
    • Description: Reducible
    • Reducible with skeletal traction under general anesthesia
    • Incidence: 17.7%
    • Surgical technique: Posterior fusion procedure
  • Type III
    • Description: Irreducible
    • Irreducible with skeletal traction under general anesthesia
    • Incidence: 29.6
    • Surgical technique: Transorally released anteriorly before posterior fusion
  • Type IV
    • Description: Bony dislocations
    • Dislocations with bony anomalies that are visualized by reconstructive computed tomography scan
    • Incidence: 0.4%
    • Surgical technique: Transoral odontoidectomy

Management

Screening

  • Down Syndrome
    • Children with down syndrome should be screened at age 5, and perhaps in again in adulthood (need citation)

Nonoperative

  • Indications
    • Fielding and Hawkins Type I
    • Type II if symptomatic, involve nsurosurgery
  • Immobilization
    • Cervical Collar
    • Halo vest
    • Sternooccipital mandibular immoblizer
    • Guided by clinical and imaging findings
  • Bed rest
  • Meds: NSAIDS, Muscle Relaxants
  • Physical Therapy
    • Indicated after immobilization period is concluded
  • Traction
    • Gradual traction may be indicated in chronic, neglected or irriducible subluxation
    • This is usually followed by immobilizatoin

Operative

  • Indications
    • Type III
    • Type IV
  • Technique
    • Transarticular screws
    • Screw-rod construct
    • Sublaminar wiring
    • Halifax clamp

Rehab and Return to Play

Rehabilitation

  • No standardized US-based rehabilitation guideline for AAI
  • After immobilization
    • Gentle range of motion
    • Soft tissue release and muscle energy
    • Therapy should be cautious and avoid forceful manipulation

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

Prognosis and Complications

Prognosis

  • General
    • Prognosis is variably, depends on etiology, severity, presence of neuro defects and timeliness of intervention
    • Overall prognosis is favorable with a timely diagnosis and appropriate surgical stabilization
    • Patients with myelopathy, neuro deficits and cord compression have much worse prognosis[7]
  • Surgical
    • Prognosis is good for patients who undergo early surgical stabilization[8]
    • Most patients with successful surgery have good functional recovery

Complications

  • Neck pain
  • Presistant headache
  • Spinal cord compression and myelopathy
  • Myelopathy
  • Spasticity
  • Radicular symptoms
  • Brainstem compression
  • Syringomyelia and Chiari malformation
  • Vertebral artery injury or insufficiency
  • Cranial neuropathy
  • Gait disturbance and ataxia
  • Bladder and bowel dysfunction
  • Sudden death

See Also

Internal

External

References

  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. ↑ 3.0 3.1 3.2 3.3 Yang, Sun Y., et al. "A review of the diagnosis and treatment of atlantoaxial dislocations." Global spine journal 4.3 (2014): 197-210.
  4. ↑ Mintken, Paul E., Lisa Metrick, and Timothy Flynn. "Upper cervical ligament testing in a patient with os odontoideum presenting with headaches." journal of orthopaedic & sports physical therapy 38.8 (2008): 465-475.
  5. ↑ Bugarini, Alejandro, et al. "Neurophysiologic monitoring during cervical traction in a pediatric patient with severe cognitive disability and atlantoaxial instability." Surgical Neurology International 13 (2022): 396.
  6. ↑ 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.
  7. ↑ Hensinger, Robert N., J. William Fielding, and Richard J. Hawkins. "Congenital anomalies of the odontoid process." Orthopedic Clinics of North America 9.4 (1978): 901-912.
  8. ↑ Henderson Sr, Fraser C., et al. "Atlanto-axial rotary instability (Fielding type 1): characteristic clinical and radiological findings, and treatment outcomes following alignment, fusion, and stabilization." Neurosurgical review 44.3 (2021): 1553-1568.
Created by:
John Kiel on 17 April 2020 19:45:05
Authors:
Last edited:
10 October 2025 01:07:06
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