Occipiocervical_Instability

Question 1

Population with most acquired occipitocervical instability

Answer 1

Down’s

Question 2

Cause of and displacement direction for traumatic occipitocervical instability

Answer 2

High energy distraction or translation.

Head most often displaces anteriorly

Question 3

Cause of acquired occipitocervical instability

Answer 3

Bony dysplasia or ligament and soft tissue laxity

Question 4

Powers Ratio

Answer 4

Basion to midvertical portion of the spinolaminar line of atlas

Divided by

Opisthion to the midvertical of the posterior surface of the atlas

> 1 anterior subluxation
< 0.55 posterior translation

Question 5

Traynelis classification of Occippitocervical instability

Answer 5

Based on direction of displacement)

Type I - anterior displacement
Type II - longitudinal displacement
Type III - posterior displacement

Question 6

Harborview classification of occipitocervical instability

Answer 6

Based on degree of instability

Stage I - minimal or non-displaced, unilateral injury to craniocervical ligaments

Stage II - minimally displaced, but MRI demonstrates significant soft tissue injuries. Stability may be based on traction test.

Stage III - gross craniocervical misalignment ( BAI or BDI > 2mm beyond normal limits)

Question 7

Harris rule of 12s

Answer 7

Basion to dens BDI

Basion line perpendicular to posterior axial line if axis

> 12mm suggests occipitocervical dissociation

Question 8

Safe zone for occipital screws

Answer 8

Within an area measuring 20mm lateral to the external occipital protuberance along the superior nuchal line

Unicortical screws 8mm with 6 total screws