The "fat" C2: a sign of fracture.

Rotational and lateral bending injuries may cause oblique fractures of the centrum (body) of the second cervical vertebra below the odontoid and plane of the superior articular facets. These fractures are often obscure because the fracture lines are frequently not perpendicular to the plane of the radiograph on either anteroposterior or lateral views. The fracture fragments may shift in relation to one another, causing the body of C2 to appear enlarged or "fat" in relation to C3. We discuss the basis of the "fat" C2 sign and illustrate a variety of fractures that can produce this change.