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Atlantooccipital Junction Anatomy


Atlantooccipital Junction Anatomy
Vertebral artery Hypoglossal canal, Posterior margin of foramen magnum, Posterior atlantooccipital membrane, Posterior arch of atlas (C1), Nuchal ligament, Ligamentum flavum, Posterior atlantoaxial membrane, Spinous process of axis (C2), Hypoplastic dens, Os odontoideum with fibrous union and narrowing of vertebral canal with head in extension, 

Lowest level of occipital bone, McGregor’s line, from posterior nasal spine of hard palate to lowest point of occipital bone., Average normal position of tip of dens is 1.32 mm above this line, with standard deviation of _2.6 mm as measured on standard lateral radiograph. Tip _4.5 mm above line is considered to indicate basilar impression. Abnormalities of dens, most often associated with skeletal dysplasias such as Klippel-Feil, Down, or Morquio syndromes, Tectorial membrane, Apical ligament of dens, Superior longitudinal band of cruciate ligament of atlas, Anterior atlantooccipital membrane, Anterior arch of atlas (C1), Articular cavity, Dens of axis (C2), Transverse ligament of atlas, Inferior longitudinal band of cruciate ligament of atlas, Anterior longitudinal ligament, Posterior longitudinal ligament
Atlantooccipital Junction Anatomy