Pseudosubluxation

Pseudosubluxation is an anatomic variant where there is anterior positioning of the body of C2 on C3. It is a normal finding seen in up to 20% of children under 16 years of age and is caused by ligamentous laxity in this age group.

This physiologic laxity can make it difficult to recognize true pathologic displacement of C2 on C3 in children. A line along the posterior arches of C1, C2 and C3 can be used to help make this distinction on lateral radiographs. In the majority of cases, this posterior cervical line passes through the anterior cortex of the posterior arch of C2; however, the posterior cervical line can also be normal if it passes just behind the anterior cortex of the posterior arch of C2, touches the anterior aspect of the anterior cortex of the posterior arch of C2, or if it comes within 1 mm of the anterior cortex of the posterior arch of C2.

Special thanks to Dr. Hansel Otero for the image.

References

• Cattell HS, Filtzer DL. Pseudosubluxation and other normal variations in the cervical spine in children. A study of one hundred and sixty children. J Bone Joint Surg Am. 1965 Oct;47(7):1295-309.
• Swischuk LE. Anterior displacement of C2 in children: physiologic or pathologic. Radiology. 1977 Mar;122(3):759-63.