Type I is an isolated hairline fracture of the ring of the axis with minimal displacement (< 3 mm) of the body of C2. The fracture may involve any part of the ring of the axis and may extend anteriorly into the body of C2. The fracture line is then oblique, involving usually one or rarely both posterior-inferior corners of the body. The disc space below the axis is normal and stable.
To rule out a type II injury, extension and flexion X-rays are obtained.