Odontoid view: margins of lateral masses (of C1) lie lateral to margins of articular pillars (of C2) – Spence’s rule. see below
CT is best diagnosis.
Diagnosis of transverse atlantal ligament rupture – 3 criteria:
MRI – most sensitive test (more sensitive than rule of Spence)
Spence's rule: ≥ 7 mm (sum of bilateral distances between dens and lateral mass) displacement of lateral masses in coronal CT view (or > 8 mm on plain XR open-mouth view to consider effects of radiographic magnification)
widening of atlantodental interval (ADI, s. predental space) in sagittal CT view (or lateral XR view): > 3 mm in adults (> 2.5 mm in females), > 4-5 mm in children.
N.B. if > 12 mm - rupture of all ligaments about dens.
Some experts say > 5 mm in adults.
Axial view of stable Jefferson fracture (transverse ligament intact):
Axial view of unstable Jefferson fracture (transverse ligament ruptured)