Anteroposterior (AP) radiograph (Fig. 60A) demonstrates lateral offset of the lateral masses of C1 relative to the lateral margins of C2 (arrows). Coronal reconstruction from cervical spine CT (Fig. 60B) confirming lateralization of the lateral masses of C2 relative to the occipital condyles as well as the lateral margins of C2. Short white lines indicate the degree of lateralization of the lateral masses of C1; if the sum is greater than or equal to 7 mm, transverse ligament disruption is likely. Axial images from cervical spine CT confirm two anterior C1 ring fractures (Fig. 60C) and a displaced fracture of the left lateral C1 ring (Fig. 60D). (Images courtesy of Jordan Renner, MD, University of North Carolina, Chapel Hill, NC, USA.)

Congenital variant (cleft/malformation), C1 ring fracture (Jefferson).