What is the primary purpose of flexion-extension views in the lumbar spine?

• A. To assess sagittal balance
• B. To evaluate bone density
• C. To assess instability
• D. To measure curvature magnitude

Answer: (C)

Flexion-extension views are a dynamic test that shows how lumbar vertebrae move relative to each other when you bend forward and backward. By comparing the positions of the vertebrae in flexion and in extension, you can detect abnormal motion between levels. If there is excessive slip (translation) or a large change in the angle between bones, that indicates instability in the segment. This information is important for conditions like spondylolisthesis or instability from degenerative or traumatic changes and helps guide treatment decisions, including whether stabilization might be needed. This study isn’t used to assess bone density, measure curvature on a single static image, or evaluate standing sagittal balance, which are done with different kinds of imaging.