Atlantoaxial Dislocation

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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_atlas


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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/20


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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/36


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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_link


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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
http://www.wheelessonline.com/ortho/myelopathyhttp://www.wheelessonline.com/ortho/myelopathy


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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)
http://www.ingentaconnect.com/content/els/03038467http://www.ingentaconnect.com/content/els/03038467


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THANK YOU

Atlantoaxial Dislocation

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