Dynamic X-rays of the Lumbar Spine: How Useful Are They?
Standing AP and lateral X-rays are often ordered when back and/or leg pain doesn't go away. The value of X-rays in diagnosing low back pain (LBP) has been questioned in the past. In this study, researchers reviewed the use of flexion-extension (F/E) X-rays for patients with LBP.

FE X-rays are taken with the patient bedning forward or extending backward as far as possible while in the standing position. This allows for a better idea of how the spine looks in a functional position. This type of X-ray is called a dynamic radiograph.

Dynamic F/E X-rays may be taken to look for spinal instability. But should every patient with LBP have this type of X-ray at the initial (first) exam? According to the results of this study, the answer is No.

A series of X-rays were taken and reviewed by three experts. The series included AP, lateral, and dynamic F/E radiographs. The panel included a musculoskeletal radiologist, a spine surgeon, and an orthopedic resident. The films were also measured and analyzed using digital measuring tools and computer software.

Only two patients out of 342 had findings on the dynamic F/E X-ray that weren't seen in standard X-rays. And neither one of those patients needed surgery. The authors suggest dynamic radiographs of the lumbar spine are only justified in surgical patients. They are not advised for routine screening of LBP.
Qusai M. Hammouri, MD, et al. The Utility of Dynamic Flexion-Extension Radiographs in the Intitial Evaluation of the Degenerative Lumbar Spine. In Spine. October 2007. Vol. 32. No. 21. Pp. 2361-2364.