Pseudosubluxation of the cervical spine is the physiological anterior displacement of C2 on C3 in children. It is common in children <7 years, and less often present in older children. Less often it is seen at C3 on C4. It is more pronounced in flexion and is of clinical significance as it can be confused with traumatic cervical injury 1.
Immature lax ligaments are considered the cause of this appearance.
Pseudosubluxation is based on a normal relationship of the upper cervical spine using Swischuk's line and the absence of prevertebral soft tissue swelling.
Swischuk's line is drawn from anterior aspect of posterior arch of C1 to anterior aspect of posterior arch of C3 2.
- the anterior aspect of posterior arch of C2 should be within 1-2 mm of this line:
- if deviated less than 2 mm: it is consistent with pseudosubluxation, but this alone is insufficient to rule out a hangman fracture
- if deviated more than 2 mm: it is indicative of true subluxation 1
- 1. Ghanem I, El Hage S, Rachkidi R et-al. Pediatric cervical spine instability. J Child Orthop. 2008;2 (2): 71-84. doi:10.1007/s11832-008-0092-2 - Free text at pubmed - Pubmed citation
- 2. Swischuk LE. Anterior displacement of C2 in children: physiologic or pathologic. Radiology. 1977;122 (3): 759-63. doi:10.1148/122.3.759 - Pubmed citation