Atlantoaxial Rotatory Displacement (AARD)

Question 1

Atlantoaxial Rotatory Displacement (AARD)

Answer 1

C1-C2 rotatory instability (fixed rotation of C1 on C2) caused by subluxation or facet dislocation

• common cause of childhood torticollis
• spectrum of disease that ranges from mild subluxation to fixed facet dislocation

Question 2

Pathophysiology

common causes include

Answer 2

• infection (~35%)
  
  • may have history of pharyngitis or otitis media
  • Grisel’s disease is the condition of AARD following a respiratory infection or retropharyngeal abscess
  • thought to be linked to lymphatic edema in area of cervical spine
• trauma (~24%)
• recent head or neck surgery (~20%)
• idiopathic
• associated conditions
  
  • Down’s syndrome
  • rheumatoid arthritis
  • tumors
  • congenital anomalies

Question 3

pathoanatomy and mechanism

Answer 3

• mechanism is thought to be related to ligamentous laxity
• transverse ligament integrity
  
  • transverse ligament is intact
    
    • spinal canal stenosis can only occur with severe rotation and facet dislocation
  • transverse ligament is ruptured
    
    • and there is a component of anterolithesis (> 5mm), then spinal canal stenosis can occur with less rotation (45 degrees)
    • vertebral arteries may also be at risk

Question 4

embryology of C2

Answer 4

embryology

• develops from five ossification centers
• subdental (basilar) synchondrosis is an initial cartilagenous junction between the dens and vertebral body that does not fuse until ~6 years of age
• the secondary ossification center appears at ~ age 3 and fuses to the dens at ~ age 12

Question 5

Occipital-C1-C2 ligamentous stability

Answer 5

provided by the odontoid process and its supporting ligaments

• transverse ligament
  
  • limits anterior translation of the atlas
• apical ligaments
  
  • limit rotation of the upper cervical spine
• alar ligaments
  
  • limit rotation of the upper cervical spine

Question 6

Classification

Answer 6

Question 7

Symptoms

Answer 7

• tilted head
• neck pain
• headache

Question 8

Physical exam

Answer 8

• ipsilateral rotation and contralateral tilt of the head in relation to the lateral mass of C1
  
  • chin rotated to the side opposite the facet subluxation (e.g. right sided facet subluxation will have chin rotated to the left)
• contra-lateral sternocleidomastoid may be spastic
  
  • sternocleidomastoid (SCM) spasm occurs on the SAME side as the chin (e.g. right sided facet subluxation will have chin rotated to the left, and left SCM will be spastic)
    
    • this protective spasticity occurs to reduce further subluxation
    • C1-C2 subluxation (and resultant chin position) is primary, SCM spasm is secondary/reactive
  • in contrast to congenital muscular torticollis where the SCM spasm occurs on the OPPOSITE side of the chin (e.g. left SCM spasm will rotate the head to the right, and chin will be on the right)
    
    • SCM spasm is primary
• reduced cervical rotation

Question 9

Radiographs

Answer 9

recommended views

• AP, open-mouth odontoid
  
  • look for variation in size and distance from midline of C2 lateral masses (reflects rotation)
• lateral
  
  • facet joint appears anterior and wedge shaped instead of normal oval shape
• cervical flexion & extension views
  
  • may be useful to exclude instability
  • may be difficult due to position of head and resisted neck motion

Question 10

Dynamic CT

Answer 10

• is diagnostic gold standard
• take CT with head straight forward, and then in maximal rotation to right and left
  
  • will see fixed rotation of C1 on C2 which does not change with dynamic rotation

Question 11

MRI

Answer 11

of little value unless neurologic symptoms

Question 12

Nonoperative

Answer 12

• soft collar, NSAIDS, exercise program
  
  • indications
    
    • subluxation present for < 1 week (traumatic or Grisel’s disease)
    • many patients probably reduce spontaneously before seeking medical attention
• head halter traction, NSAIDS, benzodiazepines, then hard collar x 3 months
  
  • indications
    
    • subluxation persists > 1 week
    • persistent torticollis in spite of soft collar (above) x 2 weeks
  • technique
    
    • small amount (5 lbs.) usually enough
    • either in hospital or at home
    • muscle relaxants and analgesics may be needed
• halo traction, then halo vest x 3 months
  
  • indications
    
    • subluxation persists > 1 mos.
    • failed halter traction x 2 weeks (above)

Question 13

Operative

Answer 13

posterior C1-C2 fusion

• indications
  
  • subluxation persists > 3 mos (or late diagnosis)
  • neurologic deficits present
  • failed halo traction x 2 weeks

Question 14

C1-C2 posterior fusion techniques

Answer 14

• approach
  
  • posterior midline cervical approach
• stabilization technique
  
  • sublaminar wiring techniques (Gallie or Brooks)
    
    • require postoperative halo immobilization and rarely used
  • posterior C1-C2 transarticular screws construct
    
    • contraindicated in patients with an aberrant vertebral artery
  • posterior C1 lateral mass screw and C2 pedicle screw construct
    
    • modern screw constructs do not require postoperative halo immobilization
• outcomes
  
  • C1-C2 fusion will lead to 50% loss of neck motion
  • Higher fusion rate in elderly compared to anterior fusion