Which imaging view is best initial for evaluating C1-C2 involvement in suspected rheumatoid arthritis?

• A. Lateral cervical spine view
• B. Open mouth view
• C. AP view
• D. MRI

Answer: (B)

In rheumatoid arthritis, cervical spine involvement often targets the C1–C2 region, where instability can have serious consequences. To screen for atlantoaxial instability, you need an image that directly visualizes the dens (odontoid process) and its relationship to the atlas. The open-mouth (odontoid) view does exactly that: it provides a frontal slice through the C1–C2 articulation, allowing assessment of the atlantodental interval and detection of anterior subluxation or misalignment of C1 over C2. This makes it the best initial radiographic projection for evaluating C1–C2 involvement.

Other views have limitations for this purpose. A lateral view can show overall cervical alignment but does not optimally visualize the dens or the anterior atlantoaxial interval. An AP view likewise fails to adequately depict the dens–atlas relationship. MRI is excellent for soft tissues, ligaments, and neural elements, but it’s not the first imaging modality used to assess bony alignment in this location; it’s typically reserved for evaluating suspected ligamentous injury or neurological compromise after initial radiographs.