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Atlantoaxial Subluxation

- See:
       - C1 / C2
       - AtlantoAxial Rotatory Subluxation in Down's Syndrome:
       - Atlantooccipital Disassociation:
       - Atlantoaxial Rotatory Fixation:
       - Atlantoaxial Subluxation in R.A.:
       - Cross Table Lateral:
       - Occipital-Atlanto-Axial Anomalies:
       - Posterior Atlanto-Axial Arthrodesis
       - Torticollis:

- Discussion:
    - refers to loss of ligamentous stability between atlas and axis;
    - occurs most often in older children and adolescents;
    - mechanism of injury in atlantoaxial rotatory subluxation is unknown, but is usually due to forced rotation of the neck along w/
           some element of lateral tilt;
           - it can occur spontaneously or after trauma;
           - complete C1-C2 dislocation is a known complication of football spearing;
    - pts complain of neck pain, occipital neuralgia, and occassionally symptoms of vertebrobasilar artery insufficiency;
    - prognosis:
           - significant potential for continued displacement of atlas on axis w/ resultant pressure on spinal cord;
           - vertebrobasilar artery insufficiency may lead to cerebral infarcts;
    - Atlanto-Axial Articulation:
           - approx 50 % of cervical rotation takes place between atlas and axis, around laterally central but anteriorly eccentric odontoid
           - lateral wall of atlas rotates to across canal of axis, physiologically decreasing opening between these 2 segments;
           - spinal canal of the atlas is large compared w/ that of other segments, which rotation around axis along w/ translational
                   displacement without pressure on the spinal cord;
           - Steele's Rule of Thirds:
                   - canal of atlas is about 3 cm in its AP diameter;
                   - spinal cord, odontoid process, and free space for cord are each about 1 cm in diameter;
                   - anterior displacement of the atlas that exceeds one centimeter may jeopardize the adjacent segment of the spinal cord;
    - Associated Conditions:
           - Down syndrome (25% of patients);
           - Rheumatiod Arthritis (adults);
           - Grisel's syndrome:
                   - atlantoaxial instability may be noted in nl child in association w/ pharyngeal infection (Grisel's syndrome);
                   - hyperemia causes demineralization of attachment of transverse ligament to anterior arch of atlas, with subsequent rotary
                           subluxation of atlas on axis or anterior atlantoaxial subluxation;
           - Klippel Feil;
           - Morquio syndrome;
           - Spondyloepiphyseal dysplasia:
           - Achondroplasia:
           - Larsen's syndrome:
    - Diff Dx:
           - Torticollis;
           - Atlantoaxial Rotatory Fixation:
           - Odontoid Fractures
           - Congenital Anomalies:
                  - os odontoideum:
                  - congenital absence of the odontoid process;

- Radiographs:
    - Lateral View:
          - ADI < 3.5 mm in flexion, implies that the transverse ligament is intact;
          - ADI 3-5 mm, transverse ligament is insufficient; (this is a type II injury);
                - in children upto 4.5 mm may be normal;
          - ADI > 5 mm:
                - indicates failure of the alar ligaments;
                - consistent w/ type III rotatory subluxation;

- Non Operative Treatment:
    - Grissel's syndrome
           - vast majority of pts w/ this form of torticollis improve spontaneously;
           - w/ the subluxation does not resolve, the child should be admited for Halter traction (in order to avoid rotatory fixation);
           - in those few cases in which persistent instability is present, stabilization by posterior atlantoaxial arthrodesis is required;
    - Children:
           - children w/ radiographic evidence of transverse ligament disruption can be treated non operatively in acute cases (less than 3
                  wks) in which there is no indication of transient or permanent neurological deficit;
           - requires treatment in halter or skull traction (NSAIDS and muscle relaxants may be given as necessary);
           - following reduction, pt is kept in traction or a halo 3 months;
           - recurrence of deformity is possible, even with this treatment, and therefore flexion-extension radiographs are needed after halo
                    has been removed;
           - ref: The delayed presentation of atlantoaxial rotatory fixation in children
    - Adults: should not be treated non operatively, since ligament healing potential is unreliable;
    - Elderly Patient: in some cases, can be managed non-operatively, because few demands are made on neck;

- Arthrodesis:
    - indications for fusion:
           - children:
                  - fusion is indicated w/ neurologic involvement;
                  - persistent anterior displacement;
                  - deformity present for more than 3 months;
                  - recurrence of deformity following 6 wks of immobilization;
           - young adults:
                  - instability, w/ or w/o pain, is treated w/ arthrodesis, because trivial trauma might lead to catastrophic cord injury;
                  - w/ moderate displacement that minimally shifts on flexion & extension views may undergo further gradual displacement of
                          atlas over time which again places the cord at risk;
    - considerations for fusion:  
           - fusion should be proceded by 2 to 3 weeks of skeletal traction
           - after skeletal traction is continued for 6 wks or use a halo cast
           - extension reduction and surgical stabilization followed by 8-12 weeks in halo jacket;
           - w/ chronic subluxation, operative reduction should not be attempt, and rather the surgeon should accept a fusion in situ or
                     should perform occiput to C2 fusion;
    - posterior C1-C2 arthrodesis:

Atlanto-axial instability and spinal cord compression in children--diagnosis by computerized tomography.

Atlanto-axial fusion for instability.

Spine fusion for atlanto-axial instability.