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ATLANTOAXIAL INSTABILITY
Abhra
9/08/2011
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Atlanto-Axial Articulation:- approx 50 % of cervical rotation takes place between atlas
and axis, around laterally central but anteriorly eccentric odontoidprocess;
- 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 othersegments, 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
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an atlantodens interval (ADI, distance betweenodontoid process and the posterior border of theanterior arch of the atlas) of greater than 3 mm
in adults and of greater than 5 mm in children asmeasured on plain radiography.
Children-increase slightly on flexion Adults-unchanged b/w flexion & extension
Transverse ligament -primary restraint againstatlantoaxial, anteroposterior movement
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Atlantoaxial instability-
predentate space >3 mm in adults
> 5 mm in children
Symptoms present -atlas impinge on the
spinal cord
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C1-C2 subluxation: Types
Anterior
Lateral
Posterior
Atlantoaxial impaction (AAI)
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AAD in RA
subluxation can occur in up to 70% of patients with rheumatoid arthritis,but frank dislocation occurs in about 25%;
approximately 11% of rheumatoid arthritis patients will develop cordcompression from atlantoaxial subluxation;
among patients that develop myelopathy, 5 years survival rate is 80% butthe 10 year survival rate is 28%, (as noted by T. Mori MD et al 1998);
C1-C2 articulation is synovial which accounts for its frequent involvementin RA;
anterior instability is much more common than posterior instability andoccurs more often in men;
-
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etiology:
results from pannus formation at synovial joints between dens, C1, &transverse ligament, resulting in destruction of transverse ligament, densor both;
transverse ligamentelongation and rupture:- stretching and destruction of these structure
allows atlasvertebra to move forward relative to the axis;- w/ C-spine flexion, atlas moves forward relative to axis;- spinal cord being compressed between posterior arch of the
atlas and the odontoid peg;
dens erosion:
in some cases odontoid is totally eroded by inflammatory reaction;
risk factors:- corticosteroid use;- seropositivity;- RA nodules;- erosive and deforming disease;
http://www.wheelessonline.com/ortho/anatomy_of_atlashttp://www.wheelessonline.com/ortho/transverse_ligament_rupturehttp://www.wheelessonline.com/ortho/anatomy_of_atlashttp://www.wheelessonline.com/ortho/anatomy_of_the_axishttp://www.wheelessonline.com/ortho/anatomy_of_atlashttp://www.wheelessonline.com/ortho/anatomy_of_the_axishttp://www.wheelessonline.com/ortho/anatomy_of_the_axishttp://www.wheelessonline.com/ortho/anatomy_of_atlashttp://www.wheelessonline.com/ortho/transverse_ligament_rupturehttp://www.wheelessonline.com/ortho/anatomy_of_atlas8/13/2019 Atlantoaxial Dislocation
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Radiology
Views
anteroposterior (AP)
AP open mouth odontoid
6-ft (1.8m) lateral views in flexion &extension
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Anterior subluxation
Predentate space> 2.5mm
Lateral subluxation
frontal view - lateral masses of Clpositioned more than 2 mm laterally with
relation to C2
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Posterior subluxation
posterior aspect of anterior arch of atlas
posterior to the anterior border of the body of
C2
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Posterior dislocation of the odontoid process.Preodontoid space measures 8 mm.Normal
2.5 -3mm
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Atlantoaxial impaction:
settling of the skull onto Cl & Cl onto C2
Erosion & bone loss at intervening joints
Lateral views- odontoid tip in relation to
McGregors(MG)* 8 mm above MG in men
9.7 mm above in women
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CLINICAL FEATURES
Earliest and most common symptom of cervicalsubluxation is pain radiating superiorly towards the
occiput .
Additional symptoms of subluxation include:
Spastic quadriparesis which is slowly progressive
Sensory findings are also common, including
painless sensory loss in the hands or feet.
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In patients with C1-C2 subluxation, transient episodes of
medullary dysfunction (such as respiratory irregularity)
associated with vertical penetration of the odontoid
process of C2 and probable vertebral artery compression. Movement of the hands in this setting may result in
paresthesias in the shoulder or arms.
Neurologic findings in patients with vertical atlantoaxial
subluxation may also include decreased sensation in the
distribution of the fifth cranial nerve, sensory loss in theC2 area, nystagmus, and pyramidal lesions
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symptoms of spinal cord compression that demand immediate
attention and intervention include [20]:
A sensation of the head falling forward upon flexion of the
cervical spine Changes in levels of consciousness
"Drop" attacks
Loss of sphincter control
Respiratory dysfunction
Dysphagia, vertigo, convulsions, hemiplegia, dysarthria, or
nystagmus
Peripheral paresthesias without evidence of peripheral nerve
disease or compression
http://www.uptodate.com/contents/cervical-subluxation-in-rheumatoid-arthritis/abstract/20http://www.uptodate.com/contents/cervical-subluxation-in-rheumatoid-arthritis/abstract/208/13/2019 Atlantoaxial Dislocation
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Ranawat class Neurological status
I No neurological deficit
II Subjective weakness with hyperreflexia and
dysesthesia
IIIA Objective weakness and long tract signs;
ambulatory
IIIB Objective weakness and long tract signs;
non ambulatory
Neurological impairment
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SIGNS
Loss of occipitocervical lordosis
Resistance to passive spine motion
Abnormal protrusion of the axial arch felt by theexamining finger on the posterior pharyngeal wall
In addition, neurologic findings appropriate to thesymptoms described above may be seen, including:
Increased deep tendon reflexes
Extensor plantar responses
Muscle weakness, spasticity, or muscle atrophy
Gait disorders
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IMAGING-MRI
particularly valuable in the assessment of cervical spine disease in RA,
because it permits visualization of the pannus producing cord
compression, the spinal cord, and bone
development of neurological dysfunction is strongly associated with MRI
evidence of atlantoaxial spinal canal stenosis, particularly in patients with
evidence of upper cervical cord or brainstem compression or subaxial
myelopathy
Bone marrow edema (BME) can be observed by MRI in patients with earlycervical spine involvement, with involvement of the odontoid process in
patients with changes at the atlantoaxial level and involvement of the
vertebral plates and the interapophyseal joints subaxiall
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one draw-back of MRI imaging is that it often underestimates the degree
of atlantoaxial subluxation when compared to plain film radiography
This was illustrated in a series of 23 patients with RA or JIA who had bothradiographs and MRI with flexion and extension views performed within a
one-month time frame [36]. After accounting for magnification on the
plain films, the measured atlantoaxial subluxation by MRI was less than
that noted on radiographs in 19 of the 23 patients; in the worst case the
measured distance differed by 7 mm.
Thus, unless flexion and extension MR images document excessive
subluxation, plain film radiography is still needed to assess atlantoaxial
stability
http://www.uptodate.com/contents/cervical-subluxation-in-rheumatoid-arthritis/abstract/36http://www.uptodate.com/contents/cervical-subluxation-in-rheumatoid-arthritis/abstract/368/13/2019 Atlantoaxial Dislocation
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Since neck positioning required for intubation prior to surgery may be fatal
among patients with RA and unrecognized C1-C2 disease, and since
subluxation is not always symptomatic, radiographic evaluation of the
cervical spine should also be considered for all patients with RA scheduled
to undergo surgery requiring manipulation of the neck for either
anesthesia or surgery
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NATURAL HISTORY
Patients with subluxation and signs of spinal cord compression have a
poor prognosis without surgery.
In this setting, myelopathy progresses rapidly and death may quickly
ensue
As an example, in a study of 21 patients with atlantoaxial subluxation and
signs of myelopathy who were medically managed medically, neurologic
deterioration occurred in 16 of 21 (76 percent) and all were unable to walk
within three years of follow up . None survived more than eight years
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MRI findings may be more helpful than plain film radiography
in determining prognosis.
As an example, among 82 patients with MRI evidence of cordcompression at the level of C1-C2, 60 percent deteriorated
with conservative management over a median of 12 months .
Those with subaxial cord compression fared better, with only18 percent worsening with time.
Among all patients, nine eventually required surgical
intervention: six due to a combination of pain and progressiveneurologic deficits, two due to pain only, and one because of
painless neurologic deterioration
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PREVENTION
Limited evidence suggests that the administration of combination therapy
consisting of disease modifying anti-rheumatic drugs may help prevent the
development of cervical spine subluxation.
195 patients with RA of recent onset (two years or less) were randomly
assigned to a regimen of sulfasalazine, methotrexate
hydroxychloroquineand prednisoloneor to sulfasalazine alone [48].
Atlantoaxial impaction or anterior subluxation developed in 2 and 7
percent of the sulfasalazine alone group, respectively, but in none of those
receiving combination therapy after two years of treatment. DMARD
treatment was unrestricted after two years
At five years of follow-up, the occurrence of anterior atlantoaxial
subluxations was significantly associated with initial single DMARD
therapy
http://www.uptodate.com/contents/sulfasalazine-drug-information?source=see_linkhttp://www.uptodate.com/contents/methotrexate-drug-information?source=see_linkhttp://www.uptodate.com/contents/hydroxychloroquine-drug-information?source=see_linkhttp://www.uptodate.com/contents/prednisolone-drug-information?source=see_linkhttp://www.uptodate.com/contents/cervical-subluxation-in-rheumatoid-arthritis/abstract/48http://www.uptodate.com/contents/cervical-subluxation-in-rheumatoid-arthritis/abstract/48http://www.uptodate.com/contents/prednisolone-drug-information?source=see_linkhttp://www.uptodate.com/contents/hydroxychloroquine-drug-information?source=see_linkhttp://www.uptodate.com/contents/methotrexate-drug-information?source=see_linkhttp://www.uptodate.com/contents/sulfasalazine-drug-information?source=see_link8/13/2019 Atlantoaxial Dislocation
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TREATMENT
Medical
surgical
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MEDICAL
Patients with severe subluxation but without signs of cordcompression are at risk for severe injury and perhaps death
due to a variety of insults. These include small falls, whiplash
injuries, and intubation.
stiff cervical collars should be prescribed for stability
Collars that are not rigid (and therefore more comfortable for
the patient) give reassurance to both physician and patient,
but provide little structural support. Spinal manipulation is contraindicated
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PHYSIOTHERAPY
role of neck muscle strengthening exercises is uncertain.
A decrease in anterior atlantoaxial subluxation was noted in a subgroup of sevenpatients with RA and unstable atlantoaxial joints during active isometric neckflexor muscle contraction
While this suggests that isometric neck flexor exercise is probably safe, theefficacy of neck flexor muscle strengthening for symptoms related to subluxation,radiographic progression, and other important patient outcomes were notassessed in this study.
In contrast to the neck flexors, isometric neck extensor muscle tighteningworsened radiographically apparent atlantoaxial subluxation in those with
unstable articulations.
Thus, while further investigation of neck flexor strengthening may be warranted,isometric exercise of the neck extensors should be avoided
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Patients with pain due to irritation of C2 nerve root, but who
do not have evidence of cord compression, may benefit from
agents used for chronic neuropathic pain.
These patients may obtain some benefit from local nerve
blocks, although the relief is generally temporary.
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SURGERY
Benefits offered by surgical management of patients with atlantoaxial
subluxation who have myelopathy include an improved survival, an
improvement in myelopathy in some patients, and a decreased risk of
neurologic progression.
The beneficial effects of surgery were illustrated in an observational study
that compared 19 patients with symptomatic atlantoaxial subluxation who
underwent laminectomy and occipitocervical fusion with those of 21
others who were managed conservatively
The five- and ten-year survival rates for those who were operated upon
were 84 and 37 percent, respectively.
In contrast, none of the 21 patients managed conservatively survived
more than eight years.
Neurologic improvement was noted in 68 percent following surgery, while
in the nonoperative group, 76 percent had neurologic deterioration
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indications for surgery:- more than 9 mm of anterior atlantoaxial subluxation places pt at high risk
for development of cord compression;- ADI of > 7 to 10 mm or posterior space (SAC) < 13 mm is contraindication
surgery in other areas of body & C-spine should be stabilized first;
ATLANTOAXIAL FUSION- most indicated for patients w/ C1/C2 subluxation which is reducible;
- results may be unacceptable if myelopathy is present;- sublaminar wiring may be contra-indicated in these patients when the SAC
is less than 12 mm;- in RA, periodontoid pannus tissue is often present and can contribute to
cord compression;- after posterior cervical fusion, this pannus tissue will often resolve;
OCCIPITOCERVICAL FUSION
- if myelopathy is present, this may be the procedure of choice;- if there is an associated irreducible atlanto-axial dislocation then consider
additional decompressive laminectomy of the atlas
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COMPLICATIONS
surgery is less successful in patients w/ servere Ranawat IIIb
lesions (non ambulatory with objective weakness);
- complications include pseudoarthrosis &
recurring myelopathy;
- pseudoarthrosis rate can be decreased by extendingfusion to occiput with wire fixation
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NEWER SURGERIES
Stereotactically-guided C1-2 transarticular
screw placement
Clinical Neurology and Neurosurgery, Volume
99, Supplement 1, July 1997 , pp. 111-111(1)
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THANK YOU