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Introduction
  • 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
  • Pathophysiology
    • common causes include
      • 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
    • pathoanatomy
      • 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
Anatomy
  • Axis Osteology
    • axis has odontoid process (dens) and body
    • 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 
  • Occipital-C1-C2 ligamentous stability 
    • 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
Classification

Fielding Classification of AARD  
Type I

 • Unilateral facet subluxation with intact transverse ligament
 • Odontoid acts as a pivot point with 1 facet subluxating anteriorly, 1 facet subluxating posterioly.
 • Most common and benign type

Type II

 • Unilateral facet subluxation with 3 to 5 mm of anterior displacement.
 • Injured Transverse ligament
 • 1 facet acts as pivot point and 1 lateral mass is displaced anteriorly

Type III

 • Bilateral anterior facet displacement of > 5 mm.
 • Rare with higher risk of neurologic involvement or instantaneous death.
 • Both lateral masses are displaced

Type IV

 • Posterior displacement of atlas (C1) (with odontoid fracture, or hypoplastic dens)
 • Rare with higher risk of neurologic involvement or instantaneous death


Physical Exam
  • Symptoms
    • tilted head
    • neck pain
    • headache
  • Physical exam
    • 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
Imaging
  • Radiographs
    • 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
  • Dynamic CT 
    • 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  
  • MRI 
    • of little value unless neurologic symptoms
Treatment
  • Nonoperative
    • 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)
  • Operative
    • posterior C1-C2 fusion 
      • indications
        • subluxation persists > 3 mos (or late diagnosis)
        • neurologic deficits present
        • failed halo traction
Complications
  • Missed diagnosis
    • diagnosis is often missed delayed
 

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