What Is Excessive Motion Testing? Flexion and Extension X-rays Explained
Excessive motion testing is a set of side-view X-rays taken with the neck or low back bent forward, called flexion, and bent backward, called extension. The films are measured to see whether any vertebra slides or tilts farther on its neighbor than intact ligaments allow. It is the test I use in Charlotte to evaluate the third of the three main spinal injuries, ligament instability, after fracture has been ruled out.
Why X-ray and Not MRI
The AMA Guides to the Evaluation of Permanent Impairment accept alteration of motion segment integrity only on plain-film lateral flexion and extension radiographs. MRI and CT are not used to rate it. The reason is mechanical. A standard MRI is taken lying still, and laxity appears only when the segment moves under load.
A Charlotte spine center showed what position alone can hide. Among 416 patients with degenerative lumbar conditions, 31 of 109 spondylolisthesis levels seen on standing radiographs, or 28%, were not visible on supine MRI (Segebarth, J Spinal Disord Tech 2015). Those were degenerative cases, not injuries, so the 28% is not a trauma figure.
What Is Measured
Two things are measured at each level. Translation is how far one vertebra slides forward or backward on the one below. Angular motion is how much the endplates tilt toward each other, compared with the levels above and below.
The AMA Guides set the thresholds. In the Fifth Edition, cervical translation greater than 3.5 mm, or cervical angular motion more than 11 degrees greater than an adjacent level, meets the threshold. In the Sixth Edition, cervical translation is expressed as greater than 20% anterior or posterior relative translation, thoracic translation is at least 2.5 mm, and lumbar angular motion must exceed 15 degrees at L1-L2, L2-L3, and L3-L4, 20 degrees at L4-L5, or 25 degrees at L5-S1, compared with adjacent-level motion. At L5-S1, translation must exceed 6% anterior or 9% posterior. These are consensus thresholds for impairment rating, and they are applied the way the Guides specify them.
What Normal Looks Like
One study digitized dynamic cervical radiographs from 75 normal subjects. Using C2-C3 as the baseline, nearly all of the differences in angular displacement between levels in flexion were less than 7 degrees (Lin, Spine 2001). The 11 degree cervical threshold sits above that range. Seventy-five subjects from a single population is a small normative sample, and I treat it as context for the threshold, not as a population norm.
How the Films Are Measured at Clear Life
I digitize the films in PostureRay, marking the vertebral body corners so the software calculates translation and angulation at each level. Clear Life has no financial relationship with PostureCo, the developer. The published evidence on the software is specific, and it is narrower than its marketing. One study found that its measurements matched hand-drawn measurements, but it used drawn rectangles in place of patient radiographs (Fedorchuk, Curr Med Imaging 2023). Another found excellent reliability for its computer-vision measurement of sagittal cervical alignment on 254 radiographs, with coauthors affiliated with the developer (Hosseini, J Clin Med 2024). I have not found a peer-reviewed study that validates its flexion and extension instability analysis specifically. So the software produces measurements. The diagnosis is mine, made from those measurements, the AMA thresholds, and the examination.
Limits of the Test
The same Charlotte study that showed the supine MRI gap also found that flexion and extension films added nothing over a single standing lateral film for detecting degenerative spondylolisthesis (Segebarth, J Spinal Disord Tech 2015). The value of motion films is measuring motion, not detecting a slip that a standing film already shows.
Timing matters too. An acutely injured patient guards against movement, and a segment that does not move cannot show excessive motion. A normal study in the first days after a crash tells me less than one taken once motion returns. That is clinical reasoning. I am not aware of a study that defines the best timing. Fracture is always excluded before motion films are taken.
For an example of how post-collision imaging findings and outcomes are documented in the peer-reviewed literature, read Dr. Justin Dick's published case report on refractory lumbar pain following a motor vehicle accident in a geriatric patient.
Frequently Asked Questions
What is excessive motion testing?
Excessive motion testing uses side-view X-rays taken in flexion and extension to measure whether a vertebra slides or tilts farther than intact ligaments allow. It is the test the AMA Guides use for alteration of motion segment integrity.
Why are flexion and extension X-rays used instead of MRI for ligament instability?
The AMA Guides accept alteration of motion segment integrity only on plain-film lateral flexion and extension radiographs. MRI is taken lying still, and laxity appears when the spine moves under load.
What measurements show spinal instability on X-ray?
Under the AMA Guides Fifth Edition, cervical translation greater than 3.5 mm or angular motion more than 11 degrees greater than an adjacent level meets the threshold. The Sixth Edition uses lumbar angular thresholds of 15, 20, and 25 degrees depending on level.
Is PostureRay accurate?
Published studies show PostureRay measurements match hand-drawn measurements on drawn renderings and are reliable for sagittal cervical alignment. No peer-reviewed study validates its flexion and extension instability analysis specifically. Dr. Justin Dick uses its measurements alongside the AMA thresholds and the physical exam.
When should flexion and extension X-rays be taken after a car accident?
Only after fracture has been reasonably excluded. Muscle guarding in the first days can limit motion, so an early normal study is less informative than one taken once motion returns. No study defines the ideal timing.
Where can I get flexion and extension X-rays after a car accident in Charlotte, NC?
Dr. Justin Dick, DC, CNMT, ARRT(N)(CT), performs and measures flexion and extension X-rays at Clear Life Scoliosis and Chiropractic Center, 8814 Rachel Freeman Way, Suite 103, Charlotte, NC 28278, phone 980-368-0766. Personal injury patients are treated on a lien basis, with no out-of-pocket payment at the time of care.
Sources and Evidence Tiers
- American Medical Association. Guides to the Evaluation of Permanent Impairment, Fourth, Fifth, and Sixth Editions.Evidence tier: Expert consensus (impairment rating guideline)
- Segebarth B, Kurd MF, Haug PH, Davis R. Routine upright imaging for evaluating degenerative lumbar stenosis: incidence of degenerative spondylolisthesis missed on supine MRI. J Spinal Disord Tech. 2015;28(10):394-397. PMID 25353204. LinkEvidence tier: Retrospective cohort
- Lin RM, Tsai KH, Chu LP, Chang PQ. Characteristics of sagittal vertebral alignment in flexion determined by dynamic radiographs of the cervical spine. Spine. 2001;26(3):256-261.Evidence tier: Cross-sectional normative study (75 subjects)
- Fedorchuk C, Comer RD, McRae C, Bak D, Lightstone DF. Validity of radiographic analyses between hand-drawn and computer-aided measurements: a double-blinded test-retest trial. Curr Med Imaging. 2023;19(9):1071-1078. PMID 36748215. LinkEvidence tier: Measurement validity study on drawn renderings, not patient radiographs
- Hosseini MM, Mahoor MH, Haas JW, et al. Intra-examiner reliability and validity of sagittal cervical spine mensuration methods using deep convolutional neural networks. J Clin Med. 2024;13(9):2573. PMID 38731102. LinkEvidence tier: Reliability study; coauthors affiliated with the software developer
About the author. Dr. Justin M. Dick, DC, is the owner and treating clinician at Clear Life Scoliosis and Chiropractic Center in Charlotte, NC. He holds dual imaging credentials as a Certified Nuclear Medicine Technologist (CNMT) and as an ARRT-registered technologist in nuclear medicine and CT, ARRT(N)(CT). He is a Senior Fellow of the CLEAR Institute, holds the ISICO World Masters credential, is a SOSORT provisional member, and is a certified DOT medical examiner on the FMCSA National Registry. He has multiple peer-reviewed publications indexed in PubMed and serves as adjunct faculty at Life, Sherman, and Palmer chiropractic colleges.
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Clear Life Scoliosis and Chiropractic Center sees personal injury and spinal imaging patients from Charlotte NC, Huntersville NC, Ballantyne NC, Matthews NC, Concord NC, Mooresville NC, Rock Hill SC, and Fort Mill SC.
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- Dr. Justin Dick's research
- Case report: refractory lumbar pain after a motor vehicle accident
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8814 Rachel Freeman Way, Suite 103
Charlotte, NC 28278
Phone: 980-368-0766
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