Pediatric emergency medicine trisk 3610 3610
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atlantooccipital and C1–C2 interspinous distances. The atlantooccipital distance
should not exceed 5 mm. The C1–C2 interspinous distance should not exceed 10
mm. Sun’s ratio, C1–C2:C2–C3, >2.5 suggests potential ligamentous instability.
Sun’s ratio, as well as a ratio of measurements of the basion to the posterior arch
of C1 (BC) and the opisthion to the anterior arch of C1 (OA), is demonstrated in
Figures 112.27 and 112.28 . If the BC:OA ratio is more than one, it signifies
atlantooccipital dislocation, an often fatal injury. Neurologic deficits may develop
from direct spinal damage or associated carotid or vertebral artery injury.
Distraction injuries may also be seen with difficult newborn deliveries. These
injuries may not be visible on a plain radiograph because the pediatric cervical
spine can transiently distract 2 in before residual radiographic evidence of spinal
column separation is present. However, the spinal cord can distract only 0.25 in
before permanent neurologic damage occurs. A CT scan should be obtained in
patients with potential atlantooccipital dislocation. An MRI scan is useful in
evaluating an infant with diminished motor activity and who is suspected of
having a distraction injury.
FIGURE 112.26 A cross section through the ring of C1 demonstrates Steele’s rule of three. The
space between the cervical cord and dens allows limited movement between C1 and C2 without
immediate neurologic compromise.
