Cervical Spine Malalignment - True or Pseudo Subluxation ?
Radiology Cases in Pediatric Emergency Medicine
Volume 1, Case 5
Loren G. Yamamoto, MD, MPH
Kapiolani Medical Center For Women And Children
University of Hawaii John A. Burns School of Medicine
     A 6 year old female was taken to a rural emergency 
department with a complaint of neck pain.  Her behavior 
was described as slightly different.  She didn't want to 
walk around and she was not moving her head much.  
The only history of trauma that was obtained was being 
thrown into a swimming pool about 32 hours ago.  She 
was difficult to examine but she was noted to have 
some tenderness over her posterior neck.  A cervical 
spine series was obtained.

View radiographs.

     AP and odontoid views were also done, but they are 
not shown here.  This lateral view shows a 
malalignment of the vertebral bodies of C2-C3.  A stiff 
collar was applied, she was placed on a spine board, 
and transferred to a children's hospital.
     During transport, she fell asleep and the transport 
took place without incident.  Upon arrival, she awoke 
and became very agitated despite the presence of her 
mother.  She complained that she couldn't breathe and 
the back of her head hurt.  She was moving her head 
around excessively despite the immobilization 
measures.  The physician on duty examined the 
radiographs and felt that the C2-C3 malalignment 
represented a normal finding, pseudosubluxation.  An 
opinion with a radiologist was sought via teleradiology, 
who agreed that this was a pseudosubluxation.  
Because of her agitation, she was taken out of cervical 
spine immobilization.  The risk of cervical spine injury 
was felt to be low because of the normal radiographs, 
the relatively benign mechanism of injury, and her 
delayed ambulatory presentation.
     After the cervical spine immobilization was removed, 
the examination of her neck revealed mild tenderness 
on palpation of the spinous processes in the mid portion 
of her neck.  Range of motion was limited in all 
directions and associated with some pain.  It was 
difficult to assess the degree of muscle spasm in her 
neck.  There were no complaints of paresthesia.  Motor 
and sensory functions were fully intact.
     A CT scan of the cervical spine was obtained to rule 
out rotary subluxation given her unwillingness to move 
her neck.  This study was normal.  Her behavior 
appeared to normalize and she was ambulating well.  
Her neck symptoms persisted.  She was discharged 
from the emergency department.  She recovered 
spontaneously without any complications.

Teaching Points:
     Rotary subluxation of one of the cervical spine 
elements (usually C1-C2) can be a difficult diagnosis to 
make.  Plain films are often difficult to interpret.  The 
patient may present with torticollis, which is usually due 
to benign muscle spasm often following a viral infection.  
Although most patients with torticollis do not have rotary 
subluxation, the task of deciding whom to evaluate 
further is difficult.  CT scanning the cervical spine can 
more definitively assess the rotational relationships of 
the cervical spine elements and more effectively rule 
out rotary subluxation.
     Developmental variants of the cervical spine in 
young children can be difficult to deal with when 
interpreting radiographs using measurement 
parameters based on adults.  
     The space between the atlas and the odontoid can 
be 4 to 5 mm in children up to age 15 years, compared 
to 2 mm for adults.  This is because the odontoid is not 
fully ossified.  The radiograph shows only the ossified 
core, while the outer layers of the odontoid are still 
cartilaginous and not visible on radiographs.
     Depending on the positioning of the child's neck, it is 
not unusual to see a straight cervical spine on the 
lateral view without the usual lordosis.  In adults, the 
absence of lordosis is an indirect sign of muscle spasm, 
possibly due to an occult fracture.  However, in 
children, the absence of lordosis is not indicative of 
muscle spasm.
     In children up to age 10 years, flexion and extension 
are greatest about C2 and C3.  C2 may appear to be 
anterior relative to C3 by as much as 5 mm.  This 
pseudosubluxation is increased if the radiograph is 
taken with the neck flexed.  This finding may be present 
in as many as one-third of all lateral cervical spine films 
in children.
     It is extremely important to distinguish true 
subluxation from pseudosubluxation.  It would be 
unwise to assume the presence of pseudosubluxation 
until this is certain.  This pseudosubluxation 
phenomenon may result in a delay in establishing the 
diagnosis of a true subluxation.  Such patients should 
be treated conservatively with cervical spine 
immobilization until the true diagnosis has been 
     The two most common causes of C2-C3 
malalignment are pseudosubluxation and a hangman's 
fracture.  To distinguish these two, Swischuk defined a 
posterior cervical line drawn from the cortex of the 
posterior arch of C1 to the cortex of the posterior arch 
of C3.  This line should pass through or be less than 
1 mm anterior to the posterior arch of C2.  If this 
distance is greater than 1 mm (possibly up to 1.5 or 2 
mm may be normal), this indicates a fracture of the 
arch of C2 (The vertebral body moves anteriorly, while 
the arch and the spinous process move posteriorly).
     Additionally, pseudosubluxations are most 
pronounced with the neck flexed.  C2/C3 malalignment 
should not persist if the neck is placed in a more neutral 
or extended position.  Persistence of the subluxation in 
extension is felt to be due to injury (non-physiologic).

Determine the Swischuk line for our patient.
     Our original patient's radiograph is below:

    Locate the posterior arch of C1 and the posterior 
arch of C3.  Draw a line through this.  Does this line 
pass within 1 mm of the posterior arch of C2 ?  The 
actual dimensions on your screen are enlarged 
depending on the degree of magnification and the size 
of your monitor so you cannot actually measure it with a 

View the Swischuk line.

     The Swischuk line is drawn on our patient's 
radiograph.  The posterior arch of C2 is pointed out; 
however, in this example, the posterior arch of C2 is 
poorly identified because the radiograph's angle is 
slightly oblique.  The distance from the Swischuk line to 
the posterior arch of C2 is about 1.6 mm.  This is more 
than the 1 mm upper normal limit described by 
Swischuk; however, other reports have indicated that 
this distance can be up to 1.5 or 2 mm.  Note that this 
radiograph is taken with the neck in flexion [Click on 
Neck to see flexion angle].  This artificially amplifies the 
degree of C2/C3 pseudosubluxation.  Ideally, the 
radiograph should be taken in a neutral or extended 
position to minimize the C2/C3 pseudosubluxation.

View another example.

     This radiograph again shows a malalignment of C2 
on C3.  Note that again, the neck is positioned in 
flexion.  Is this a pseudosubluxation or a true 
subluxation?  Identify the posterior arches of C1 and 
C3.  Draw a line connecting these points.  Does this line 
pass within 1 mm of the posterior arch of C2 ?
     Drawing the Swischuk line on this radiograph is 
easier.  The posterior arches of C1, C2, and C3 are well 

     This Swischuk line intersects the posterior arch of 
C2.  It indicates good alignment of this region despite 
the apparent malalignment of the vertebral bodies.
     You should be confident that you can identify the 
landmarks necessary to draw the Swischuk line.  This is 
important in distinguishing pseudosubluxation from a 
true subluxation.  Pseudosubluxation occurs commonly 
(up to 33%); therefore, it is very likely that you will need 
to draw the Swischuk line several times a day.

View another example.

     This radiograph also shows malalignment of C2 on 
C3.  It again shows modest flexion.  Draw the Swischuk 
line on this radiograph.  Drawing the Swischuk line on 
this radiograph is considerably more difficult because 
the posterior arch of C1 is not as obvious.  The arch of 
C1 is positioned obliquely in this film, thus you can 
actually see the arch (it resembles a loop).

     The gap between the Swischuk line and the 
posterior arch of C2 is about 1 mm.  This is at the upper 
normal limit described by Swischuk, but other reports 
have indicated that this can be up to 1.5 or 2 mm.

View this radiograph again.

    This radiograph was taken as part of a foreign body 
series in a patient with a bronchial foreign body.  There 
was no suspicion of cervical spine injury.  Note that the 
neck is flexed.  This amplifies the C2/C3 
pseudosubluxation.  Neck flexion also increases the 
width of the prevertebral soft tissues.  In a properly 
positioned radiograph, the prevertebral soft tissue 
thickness should be about half the width of the vertebral 
bodies (as demonstrated in the two previous 

     If this space is widened, it suggests the presence of 
a retropharyngeal abscess in a febrile patient with upper 
airway symptoms or soft tissue edema or bleeding from 
an occult cervical spine fracture in a trauma patient.  In 
the [Neck-3] radiograph, the prevertebral soft tissues 
are excessively wide, but not because of an abscess or 
bleeding.  This finding is purely due to positioning in this 
case.  In this case, taking the radiograph with the neck 
extended will probably "cure" the patient of the 
pseudosubluxation and the prevertebral soft tissue 

     Fassier F.  C1-C4 Fractures and Dislocations.  In:  
Letts RM (ed).  Management of Pediatric Fractures.  
New York, Churchill Livingstone, 1994, pp. 807-831.
     Ozonoff MB.  The Spine.  In:  Ozonoff MB.  Pediatric 
Orthopedic Radiology.  Philadelpha, W.B. Saunders 
Company, 1992, pp. 1-7.
     Woodward GA.  Neck Trauma.  In:  Fleisher GR, 
Ludwig S.  Texbook of Pediatric Emergency Medicine, 
third edition.  Baltimore, Williams & Wilkins, 1993, pp. 
     Swischuk LE.  Anterior Displacement of C2 in 
Children:  Physiologic or Pathologic?  A Helpful 
Differentiating Line.  Radiology 1977;122:759-763.
     Chung SMK.  The Neck.  In:  Handbook of Pediatric 
Orthopedics.  New York, Van Nostrand Reinhold, 1986, 
pp. 43-52.

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Web Page Author:
Loren Yamamoto, MD, MPH
Associate Professor of Pediatrics
University of Hawaii John A. Burns School of Medicine