Jefferson fracture refers to fracture of which vertebra?

• A. Atlas (C1)
• B. Axis (C2)
• C. C3
• D. C4

Answer: (A)

Jefferson fracture is a fracture of the atlas, the first cervical vertebra (C1). It’s a burst-type injury of the ring of C1 produced by axial loading on the skull, such as a dive or a heavy landing. Because the damage involves the ring of C1 rather than the dens on C2, the axis is usually spared, which helps distinguish it from odontoid or other C2 injuries. On imaging, the ring of the atlas breaks in multiple places and the lateral masses can separate outward, often widening the space seen on radiographs of the neck. This makes it clear that the fracture involves the atlas (C1) rather than C2, C3, or C4.