Pediatric emergency medicine trisk 3612 3612

FIGURE 112.28 Examples of methods to assess occipital/C1 relationships. A, C1 anterior arch;
B, basion (anterior margin of foramen magnum); C, anterior portion of the posterior ring of C1;
O, opisthion (posterior margin of foramen magnum); and D, tip of the dens (odontoid process).
These landmarks may not be easily visible on all radiographs. A BC:AO ratio of more than 0.9
to 1.0 suggests anterior dislocation or subluxation of the atlantooccipital joint. A BD distance of
more than 10 to 12.5 mm should be suggestive of atlantooccipital dislocation. A C1–C2:C2–C3
ratio of more than 2.5 suggests injury to the tectorial membrane and ligamentous instability.