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
- Associated with vertebral anomalies
- 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)
X-ray
- 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