C2-C3 Subluxations: Pseudo and True

The term subluxation is often misused and misunderstood. There are many definitions for subluxation depending on who is using the term, be it orthopedic surgeon, radiologist or chiropractor. I don't want to get into the subluxation discussion in this article. For the purposes of this article, I will simply state that a radiographic subluxation is a disrelationship between two contiguous vertebrae due to either trauma, disease or both. Regarding traumatic injuries of the cervical spine, a subluxation generally can be demonstrated radiographically in the lateral projection. Most experts will agree with the findings of displacement of more than 3 mm of one vertebral body in relationship to another.¹ To add to the confusion, there is an entity called a pseudosubluxation which further muddles the terminology. It is this term I would like to review.

The pseudosubluxation occurs when there is an anterolisthesis of C2 on C3 in patients under the age of 16. The pseudosubluxation has been reported as common in young patients and is considered to be of no clinical significance. Several have reported this entity in children up to the age of 14 and even as old as 16 years. Keats and Lusted² describe it as a normal finding. The pseudosubluxation appears exactly like a subluxation except that it occurs at C2/3 only and generally measures no more than 2 mm. The disrelationship is always an anterolisthesis of C2 on C3.

The difficulty arises when a young patient has experienced a traumatic injury, most commonly an auto accident, and presents with all the symptoms of a hyperflexion sprain. How do we differentiate the true traumatic subluxation injury from the pseudosubluxation? This differentiation is not easy, and you may feel that it is unnecessary if the patient has clinical symptoms and a clear history of injury. This is probably a reasonable opinion to have, as long as one does not need to defend one's opinion in court or to an insurance carrier. I think we should be aware of this entity and know how to defend our opinion as to whether or not there is a true subluxation present.

It has been stated that the pseudosubluxation is due to the immature musculature in infants and children, or possible improper positioning of the patient. There are, of course, true subluxations at the C2/3 level in children the same as adults. The important point is to be able to differentiate the two entities.

Sischuk performed radiographic studies on 500 children up to the age of 14 and has arrived at the following technique for differentiating the pseudosubluxation from the true subluxation. On a flexion view of the cervical spine, a line is drawn through the anterior cortex of the posterior arches of C1, C2 and C3. In the normal situation, or when a pseudosubluxation is present, the line is considered normal if it touches the anterior aspect of the cortex of C2 or comes within 1 mm of the cortex of C2. If a true subluxation exists, the posterior cervical line will miss the posterior arch of C2 by 2 mm or more. If the line misses the arch by 1.5 mm, the patient has suffered from a traumatic incident; a true subluxation complex is present.

For an adult patient, this procedure is not necessary to document a subluxation. However, if there is a C2-3 anterior subluxation evident on a young patient, at least under the age of 14, I would recommend checking this technique out -- just in case you need to ever defend your opinion about the existence of a subluxation, which occasionally happens.

References

1. Sischuk LE. Radiology 1977, vol. 122, p. 756.

    

2. Keats T, Lusted L. Atlas of Roentgenoraphic Movement, 5th ed., 1985.