Pediatric emergency medicine trisk 3609 3609

Abnormal posterior cervical line is also shown. E: Dens fracture (arrow ) with anterior
subluxation of the dens on the body of C2. (A : Reprinted with permission from Swischuk L.
Emergency Radiology of the Acutely Ill or Injured Child . 2nd ed. Baltimore, MD: Williams &
Wilkins; 1986:572.)

Atlantoaxial Subluxation
Atlantoaxial (AA) subluxation is a result of movement between C1 and C2
secondary to transverse ligament rupture or a fractured dens ( Fig. 112.25 ).
Ligament instability may be precipitated by tonsillitis, cervical adenitis,
pharyngitis, arthritis, or connective tissue disorders. Approximately 15% of
patients with Down syndrome have radiographically demonstrated AA
subluxation and therefore should be discouraged from contact sports. The
presence or absence of AA subluxation in patients with Down syndrome, once
believed to be a static phenomenon, may actually be transient and/or progressive.
This ligament instability may progress to ligament rupture with minor trauma.
Subluxation caused by a transverse ligament disruption is evidenced by a widened
predental (periodontoid, atlantodental interval) space on a lateral radiograph ( Fig.
112.25 ). Rotary subluxation can be classified as follows: type I (no displacement
of C1), type II (3 to 5 mm C1 on C2 anterior displacement), type III (more than 5
mm C1 on C2 anterior displacement), and type IV (posterior displacement of C1
on C2). Normal predental measurement in children is less than 5 mm compared
with less than 3 mm in adults. This space is wider in children than in adults for the
same reasons as described for pseudosubluxation. Steele’s rule of three states that
the area within the ring of C1 consists of one-third odontoid, one-third spinal cord,
and one-third connective tissue ( Fig. 112.26 ). Therefore, limited space is
available for dens movement or predental space widening without neurologic
compromise. Neurologic symptoms are often not seen until the predental space
exceeds 7 to 10 mm. A dens fracture is the cause of AA subluxation more often
than ligamentous disruption in a young child because the weakest part of the
musculoskeletal system in a child is the osseous component ( Fig. 112.25 ).
Neurologic damage can occur from direct spinal cord injury or secondarily from

vertebral artery damage.

Cervical Distraction Injuries
Cervical distraction injuries may result from rapid acceleration- or decelerationtype incidents, such as high-speed motor vehicle collisions, pedestrian accidents
or infant abusive head trauma ( Fig. 112.27 ). This type of injury, although
uncommon, is reported to be approximately 2.5 times more common in children
than in adults. Cervical distraction injuries may be obvious or subtle on the initial
lateral radiograph. Measurements for potential distraction injuries include the