When performing an AP projection, RPO of the Lumbar spine, the MSP forms what degree of angulation with the image receptor?

• A. 45 degrees
• B. 0 degrees
• C. 30 degrees
• D. 60 degrees

Answer: (A)

Opening the lumbar joints in an AP projection done in a right‑posterior oblique position relies on placing the MSP at the right amount of obliquity relative to the image receptor. When the MSP is rotated about 45 degrees, the lumbar zygapophyseal joints come into true profile and the vertebral structures are demonstrated with minimal superimposition. This specific angle is the standard to visualize those joints clearly on an AP oblique view. If there’s no rotation, the joints are obscured by overlapping vertebrae; too little rotation (around 30 degrees) won’t open the joints adequately, and excessive rotation (about 60 degrees) can distort anatomy and shift structures out of the intended view.