= AARF = ATLANTOAXIAL ROTATORY SUBLUXATION (AARS) = ATLANTOAXIAL ROTATORY FIXATION (AARF) = SPONTANEOUS HYPEREMIC DISLOCATION = ATLANTOAXIAL ROTATORY / ROTARY DISLOCATION = DISTENTION LUXATION = NASOPHARYNGEAL TORTICOLLIS

= nontraumatic subluxation / rotational disorder of atlantoaxial joint leading to limited rotation / fixation of neck comprising many different entities

Cause: idiopathic spontaneous

1. increased ligamentous laxity: rheumatoid arthritis, Marfan syndrome, Down syndrome, Morquio syndrome
2. congenital abnormality: incomplete odontoid process, incomplete transverse ligament
3. infection: sinusitis, otomastoiditis, otitis media, pharyngitis, adenotonsillitis, cervical / retropharyngeal / tonsillar abscess = Grisel syndrome
   (= not associated with trauma or bone disease primarily in children) ← hyperemia + pathologic ligamentous relaxation

Predisposed: cervical dystonia, post surgery

May be associated with: ipsilateral contracted SCMM

• history of insignificant cervical spine trauma / upper respiratory tract infection
• limited painful neck motion = painful torticollis
• head held in “cock-robin” position = rotation + flexion + tilt of head contralateral to direction of rotation with inability to turn head that does not resolve within 5–7 days after injury

X-ray (Dx difficult to make):

• atlanto-odontoid asymmetry (open mouth odontoid view):
  • decrease in atlanto-odontoid space + widening of lateral mass on side ipsilateral to rotation
  • increase in atlanto-odontoid space + narrowing of lateral mass on side contralateral to rotation
• atlantoaxial asymmetry remains constant with head turned into neutral position
• posterior arch of C1 not identified in true lateral projection
• obscuration of craniovertebral junction in true lateral view

CT (dynamic with 3D reconstruction [a] with head in resting position [b] with maximal contralateral rotation):

• facet displacement in neutral head position
• asymmetrically fixed C1-C2 rotation
  Rotation up to an average of 79° in adult volunteers, loss of contact of articular facets of C1 and C2 during rotation as high as 74–85% in physiologic conditions. Therefore, a diagnosis of subluxation of the atlanto-occipital joint should not be made based solely on the CT appearance of this joint.

MR:

• disruption of alar + transverse ligg.
• spinal cord compression (rare)

Types:

• I <3 mm anterior displacement of atlas on axis = rotatory fixation within normal range of movement (most common)
  Injury: intact alar + transverse ligaments
  • pivot around dens, NO anterior displacement of atlas
• II 3–5 mm anterior displacement of atlas + unilateral displacement of lateral mass of atlas ← restraint by alar lig.
  Injury: transverse ligament
  • center of rotation shifted to one of lateral masses
  
  
• III >5 mm anterior displacement of atlas + anterior displacement of both lateral masses
  Injury: deficiency of both (alar + transverse) ligaments
• IV posterior displacement of atlas on axis (rare)
  Injury: deficiency of both (alar + transverse) ligaments

DDx: torticollis (atlantoaxial symmetry reverts to normal with head turned into neutral position)