Volume 1, Case 5 Answers

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 ascertained.

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.

Neck

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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 ruler.

View the Swischuk line.

Align

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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.

Neck-2

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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 defined.

Align-2

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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.

Neck-3

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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).

Align-3

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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.

Review this radiograph again.

Neck-3

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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 radiographs Neck and Neck-2]). 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 widening.

References

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. 1124-1142.
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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 Loren Yamamoto, 
      MD, MPH Associate Professor of Pediatrics University of Hawaii John A. Burns 
      School of Medicine loreny@hawaii.edu