Dynamic X-rays

Dynamic X-rays, also called flexion-extension views, are X-rays taken while you bend the spine forwards and then backwards. Comparing the two positions shows how the vertebrae move relative to each other. The purpose is to detect abnormal or excessive movement — instability — that would not be apparent on a single static picture.

Ordinary X-rays capture the spine frozen in one position. By taking films at the extremes of movement, a radiologist can measure whether one vertebra slides too far forward, backward or opens up abnormally as you bend. If a vertebra shifts more than a defined amount between the flexion and extension views, this indicates that the segment is not being held stable — useful, for example, in assessing a slipped vertebra or checking a spine before or after fusion surgery.

You will be asked to bend as far forward as is comfortable, and then to lean back, holding each position briefly while the image is taken. The radiographer will guide you and will only ask for movement within your comfortable range. The test is painless in itself, though moving may reproduce familiar symptoms; you should tell staff if anything is too uncomfortable. It uses the same low X-ray dose as standard films, and pregnancy is checked as usual.

Instability is defined by movement, so it can be invisible on a still image and only appear when the spine is put through its range. Dynamic X-rays capture that movement, helping to confirm whether a slipped vertebra is stable or shifting, and whether abnormal motion might be contributing to symptoms. This information can be important in deciding whether stabilising surgery, such as a fusion, is appropriate, and in checking how a spine behaves after previous surgery.

• —Royal College of Radiologists — iRefer: Making the Best Use of Clinical Radiology
• —UK Health Security Agency — Ionising Radiation: Patient Dose Information
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.