Flexion-extension radiographs of the spine are primarily used to assess which of the following?

• A. Acute fracture extent.
• B. Facet joint arthritis.
• C. Bone mineral density.
• D. Functional instability and vertebral translation.

Answer: (D)

Flexion-extension radiographs capture how the spine moves when bending forward and backward, looking for abnormal movement between adjacent vertebrae. They are most informative for detecting functional instability—specifically, excessive anterior-posterior translation or angular motion from one position to the other. When instability is present, one vertebra may slip relative to the one below, which these dynamic views will reveal, even if static radiographs look relatively normal. That’s why this technique is the standard for assessing functional instability and vertebral translation.

These views aren’t primarily used to measure acute fracture extent, which is better assessed on neutral radiographs or cross-sectional imaging like CT or MRI. Bone mineral density isn’t evaluated with flexion-extension X-rays but with a DEXA scan. Facet joint arthritis is a degenerative change seen on imaging but isn’t a dynamic finding and isn’t diagnosed mainly from movement between positions.