Basilar Invagination

Classification

Primary (congenital)
- Associated with vertebral anomalies
  - atlanto-occipital fusion
  - hypoplasia of the atlas
  - Klippel- Feil
- Associated with skeletal dysplasias
  - achrondroplasia
  - Spondyloepiphyseal dysplasia
  - Morqios Syndrome
Secondary

Skull softening disorders

severe osteoporosis
Osteomalacia
Rickets
Pagets
Osteogenesis imperfecta
RA
Neurofibromatosis

Pathology

Odontoid may impinge on cord

medulla
Cerebellum
Vertebral arteries (VBI)
Aqueduct of Sylvius (Hydrocephalus)

XRay

McRaes line

connects anterior + posterior margins of the foramen magnum
( Basion + Opisthion)
odontoid should not project above this line

Chamberlains line

From the posterior margin of the hard palate to the posterior margin of the foramen magnum
Tip of the odontoid should not project more than 3mm above this line

McGregors line

From the posterior margin of the hard palate to the most caudal part of the occiput
tip of the odontoid should not project > 4.5 mm above this line

Treatment

Halo

Preop Halo traction to reduce subluxations & pull the odontoid out of the foramen magnum

Occipito-cervical fusion

technique

midline incision - from extension occip protuberance to ~ C4 level
subperiosteal dissection to expose occiput & cervical laminae
wires passed

under C1 laminae
through drill hole in C2 SP
through hole in outer table at external occipital protuberance

decorticate + make trough in occiput for graft
BG from posterior iliac crest harvested, laid, wires passed through drill holes in graft & then tied over
cervical orthosis for 3/12

Webpage Last Modified: 18 February, 2010