Atlantoaxial_Instability

Question 1

Atlantiaxial instability in Morquio’s Syndrome

Answer 1

Accumulation of keratin sulfate

Odontoid hypoplasia

Fusion if greater than 5 mm instability even if asymptomatic

Spinal cord compression can be due to extra-dural soft tissue thickening. Posterior occipitocervical fusion

Question 2

Anterior Atlantic-dens interval

Answer 2

Adult normal 3 mm or less; > 3.5 mm considered unstable

Pediatric 5 mm or less

Instability alone is not an indication for surgery.

> 10mm is itself an indication for surgery

Question 3

C1-2 SAC ( space available for the cord)

Answer 3

In adults with RA < 14mm increased risk for neurological injury and indication for surgery

Question 4

Lateral mass displacement overhang and stability

Answer 4

Rule of Spence

Sum > 6.9mm (8.1mm with radiographic magnification) is suggestive of transverse ligament rupture and considered unstable

Question 5

Down Syndrome ADI

Answer 5

Asymptomatic <4.5mm - unrestricted activities

Asymptomatic between 4.5-10mm - at risk and restricted from head contact activities

ADI >10mm or any symptomatic patient with cord changes on MRI - fusion

Symptomatic between 4.5-10mm without cord changes MRI - closely observed and restricted activity

Question 6

Posterior Atlanto-dens interval PADI

Answer 6

<14mm is indication for surgery

> 13mm is the most important radiographic finding to predict neurological recovery after decompressive surgery

Question 7

Rheumatoid C1-2 fusion

Answer 7

AADI > 10mm
PADI < 14 mm
Progressive myelopathy

Transarticular C1-2 screws eliminates halo

Occipitocervical fusion if basilar invagination

Question 8

Rheumatoid odontectomy

Answer 8

Rarely indicated

Secondary procedure with residual anterior cord compression due to pannus that fails to resolve after posterior spinal fusion

Pannus often resolves after posterior fusion alone due to decrease in instability

Question 9

Treatment of os ofontoideum

Answer 9

Observation unless neurologic deficit or instability

Posterior C1-2 fusion

Question 10

Risk factors for type II odontoid fracture (8)

Answer 10

6mm or more displacement - >50% nonunion - strongest reason to opt for surgery

Age over 50
Fx comminution
Fracture gap > 1mm
Angulation > 10 degrees
Delay in treatment > 4 days
Posterior redisplacement > 2mm
Smoker

Question 11

Treatment of atlas fractures

Answer 11

Depends on integrity of transverse ligament

Dickman transverse ligament injury classification
Type I - intrasubstance tear - C1-2 fusion
Type II - bony avulsion at C1 lateral mass - halo vest treatment successful 75%