What is the recommended tube angulation for a lateral radiograph of the L5-S1 joint?

• A. 0 degrees
• B. 5-8 degrees caudal
• C. 15 degrees cephalad
• D. 20 degrees caudal

Answer: (B)

When imaging the L5–S1 region from the side, a slight caudal tilt of the x-ray tube helps the beam run parallel to the disc space at that junction. The L5–S1 area sits at the bottom of the lumbar curve and has a natural angle due to lordosis, so angling the tube a little downward aligns the central ray with the plane of the L5–S1 disc space. This reduces overlap of the bones and opens the joint space enough to evaluate for degenerative changes or misalignment.

The best balance is a small caudal angle in the range of about five to eight degrees. Too little angle can leave the joint space obscured by overlapped anatomy, while too much angle—such as a large caudal tilt—can distort the anatomy and misrepresent the joint or adjacent structures. A modest caudal angle consistently improves visualization of the L5–S1 joint on a lateral view.