A 7-year-old female is brought in by paramedics in 
full C-spine immobilization after being involved in a 
motor vehicle accident.  According to her parents, the 
unrestrained child was sitting in her restrained mother's 
lap on the passenger side when the passenger side of 
the car was broadsided by another vehicle.  The child's 
head was thrown into the dashboard, and she sustained 
severe injuries to the face and scalp.
     Upon arrival in the ED, the patient is crying and 
responsive to all stimuli.  There are multiple facial 
lacerations, a large scalp laceration, and facial 
edema/ecchymosis.
     A lateral neck radiograph is taken.

View lateral neck radiograph.

     The hangman's fracture is an unstable fracture of 
the C2 pedicles, with forward displacement of C1 and  
the body of C2 on C3.  This traumatic spondylolisthesis 
of C2 is the result of hyperextension of the head relative 
to the neck.  
     Motor vehicle accidents, hanging and 
hyperextension can cause these fractures by creating 
a hyperextension or flexion force (leverage) of the 
cervical spine as a fulcrum.  The upper portion of the 
cervical spine (skull, C1, C2) then separates from the 
lower cervical spine.  Hyperextension will initially cause 
fracture of the C2 neural arch (pedicles) and disruption 
of the anterior ligaments.  The return to neutral position 
will then cause the body of C2 to become anteriorly 
displaced over C3.
     Lateral neck radiographs are extremely helpful, and 
the fracture of the neural arch is usually easily seen.  
Oblique views are also helpful.  AP views do not 
contribute much.  CT scans are not as helpful as in 
other cervical fractures.
     If the neural arch fracture is not evident on the 
lateral neck view in a hangman's fracture, it may 
resemble a benign "pseudosubluxation" of C2 on C3.  It 
is essential to properly identify a hangman's fracture.  
DO NOT mistake this for a "pseudosubluxation".  Refer 
to Case 5 of Volume 1 (Cervical Spine Malalignment - 
True or Pseudo Subluxation ?) for a more detailed 
discussion of cervical spine "pseudosubluxations".

View the anatomic markers on the lateral neck
     radiograph.

     The white arrow points to the fracture of the pedicle 
(neural arch) of C2.
     In the lateral neck radiograph of a hangman's 
fracture, the C2 vertebral body is displaced superiorly, 
and the inferior articular facets of C2 are displaced 
inferiorly.  The C2 pedicle fractures are anterior to the 
inferior articular facets and posterior to the superior 
articular facets.  With the loss of bony support, the C2 
vertebral body will usually move anteriorly relative to 
C3.
     The diagram shows three lines drawn along the 
cervical spine.  From left to right on the diagram, these 
are the anterior cervical line, the posterior cervical line, 
and the spinolaminal line.  A fourth line that is often 
drawn over the spinous processes is not shown here.
     These lines show only minimal disruption in the 
C2-C3 region.
     In a hangman's fracture, the anterior and posterior 
cervical lines will usually be abnormal because of the 
anterior displacement of C2 on C3.
     The spinolaminal line is usually not intact between 
the C2 spinous process base and the C1 posterior arch, 
with the posterior arch of C1 displaced anterior to the 
C2 spinous process base.  This is the result of the C2 
body carrying the odontoid process when it moves 
forward on C3.  C1 and the skull follow the C2 forward 
movement because the occipitoatlantoaxial joints are 
not damaged.
     The spinolaminal line from C2 to C7 may remain 
intact because the inferior articular facets of C2 remain 
in their usual location, and the apophyseal joints 
between the C2 inferior articular facets and the C3 
superior articular facets remain unchanged.
     A patient with a C2 hangman's fracture may present 
in a variety of ways, often with a strong association with 
facial and scalp injuries.

     In a patient with a hangman's fracture, when the 
fracture of the neural arch (pedicle) of C2 is not visible 
on the lateral neck view (an uncommon occurrence), 
the only evidence of the fracture may be modest 
malalignment of C2-C3.  This can also be seen in a 
benign pseudosubluxation.  Distinguishing a benign 
C2-C3 pseudosubluxation from a TRUE subluxation 
associated with a hangman's fracture is critical.  Refer 
to Case 5 of Volume 1 (Cervical Spine Malalignment - 
True or Pseudo Subluxation ?) for a more detailed 
discussion of cervical spine "pseudosubluxations".
     In general, the C2-C3 pseudosubluxation differs 
from the hangman's fracture in several ways:
     1.  The injury mechanism history for a 
pseudosubluxation is generally more benign.   A 
hangman's fracture is typically an 
acceleration/deceleration mechanism (motor vehicle 
crash) or a hanging mechanism.
     2.  Clinically, a patient with a pseudosubluxation will 
appear to have sustained much less trauma than a 
patient with a hangman's fracture.
     3.  A pseudosubluxation is ONLY seen on lateral 
neck radiograph views that are positioned without 
lordosis (i.e., in flexion, or neutral).  If C2-C3 
malalignment is noted on a lateral neck radiograph with 
good lordotic (extension) positioning, this is probably a 
TRUE subluxation (a hangman's fracture), and NOT a 
pseudosubluxation.  Since the occiput of most children 
is large, most lateral neck radiographs taken on children 
strapped to spine boards, will frequently show the neck 
in neutral or flexed positioning.
     4.  A visible fracture of the neural arch is usually 
evident on the lateral neck view in a hangman's 
fracture.  The absence of a visible fracture does not rule 
out a hangman's fracture since it may be difficult to 
visualize radiographically at times.
     5.  The Swischuk line, may be helpful in identifying 
some hangman's fractures.  This line is drawn from 
the anterior aspect of the posterior arch of C1 to the 
anterior aspect of the posterior arch of C3.  The anterior 
aspect of the posterior arch of C2 should be within 1-2 
mm of this line.  If it is deviated more than 2 mm, this is 
indicative of a true subluxation.  If it is deviated less 
than 2 mm, this is consistent with a pseudosubluxation, 
but this alone is insufficient to rule out a hangman's 
fracture.  Note that in our patient with the hangman's 
fracture, the Swischuk line is in good alignment in the 
presence of a hangman's fracture.

View Swischuk line.

     The left image is our patient with the hangman's 
fracture.  The right image is a normal patient whose 
neck is positioned in flexion showing C2-C3 
pseudosubluxation.  The Swischuk lines are in good 
alignment in both images.

     6.  Clinically, if one is confident that a 
pseudosubluxation is the reason for the C2-C3 
malalignment, one could reposition the patient to obtain 
a repeat lateral neck radiograph in extension (lordosis).  
If the C2-C3 malalignment resolves, this is consistent 
with a pseudosubluxation.  If the C2-C3 malalignment 
persists, this is consistent with a true subluxation.  
However, this maneuver is often not clinically useful 
since cervical spine movement should be minimized 
until cervical spine fractures and/or instability have 
been ruled out.
     7.  In uncertain cases, a CT or MRI scan may be 
necessary to rule out a hangman's fracture.

References:
     Cornelius R, Leah J.  Imaging evaluation of cervical 
spine trauma.  Neuroimaging Clinics of North America 
1995;5(3),451-463.
     Fesmire F, Luten R.  Pediatric cervical spine.  
Journal of Emergency Medicine 1989;7:133-142.
     Roberge R.  Facilitating cervical spine radiography in 
blunt trauma.  Emergency Medicine Clinics of North 
America 1991;9(4):733-742.
     Daffner R.  Evaluation of cervical vertebral injuries.  
Seminars in Roentgenology 1992;27(4); 239-253.
     Gerlock A, et al.  The cervical spine in trauma.  WB 
Saunders Company, Philadelphia, 1978.