Flexion-Extension Radiographs¶
Definition¶
Flexion-extension radiographs are dynamic lateral radiographs obtained with the patient actively flexing and extending the spine. They are used to evaluate segmental instability — abnormal motion between adjacent vertebrae — that may not be apparent on static images.
Technique¶
Patient Positioning¶
- Flexion view: patient actively bends forward as far as tolerated while a lateral radiograph is obtained
- Extension view: patient actively arches backward as far as tolerated while a lateral radiograph is obtained
- The patient must perform the motion actively (not assisted by the technologist) to prevent iatrogenic injury in the setting of ligamentous instability
- Standing or seated positioning is preferred over supine
Key Technical Points¶
- Adequate range of motion is essential — if the patient is in spasm or splinted by pain, the study may be falsely negative
- The study should be delayed 2–4 weeks after acute injury to allow muscle spasm to subside and reveal underlying ligamentous instability
- Each view should be compared to the neutral lateral
- Digital imaging with post-processing can help optimize visualization
Indications¶
- Suspected ligamentous instability after trauma (when initial imaging is equivocal)
- Evaluation of spondylolisthesis — to determine if the slip is fixed or dynamic
- Assessment of pseudarthrosis after spinal fusion — motion at the fused segment indicates non-union
- Chronic neck or back pain with suspected segmental instability
- Pre-surgical planning for fusion procedures
- Follow-up of known instability or post-surgical assessment
Interpretation¶
Measurements¶
| Parameter | Normal | Abnormal (Suggests Instability) |
|---|---|---|
| Sagittal translation (change in alignment between flexion and extension) | <2 mm (cervical), <3 mm (lumbar) | ≥3.5 mm (cervical), ≥4.5 mm (lumbar) |
| Angular change (change in disc angle between flexion and extension) | <11° per segment | ≥11° at a single segment (cervical), ≥15° (lumbar) |
What to Look For¶
- Compare the three contour lines (anterior body, posterior body, spinolaminar) on flexion and extension views
- Measure translation at each level — the amount one vertebra slides relative to the next
- Measure segmental angulation — the change in angle between adjacent endplates
- In post-fusion patients, any motion across the fused segment suggests pseudarthrosis
Clinical Pearl
Flexion-extension radiographs are most useful when obtained at least 2 weeks after acute injury. In the acute setting, pain and muscle spasm limit motion and can mask underlying instability, producing a false-negative study. If clinical suspicion for ligamentous injury is high in the acute setting, MRI is the preferred study — it can directly visualize ligamentous disruption without requiring patient motion.
Limitations¶
- Muscle spasm in the acute setting limits motion and reduces sensitivity
- Patient cooperation is required — inadequate motion produces non-diagnostic studies
- Only evaluates sagittal plane instability — does not detect rotational or lateral instability
- Cannot visualize soft tissue structures (disc, ligaments, cord)
- Radiation exposure — two additional views beyond the standard series
- MRI has largely replaced flexion-extension films for acute ligamentous injury evaluation
Key Points¶
- Flexion-extension radiographs are dynamic studies that evaluate segmental instability
- Patient must perform motion actively — never passively assisted
- Best performed 2–4 weeks after acute injury when muscle spasm has subsided
- Sagittal translation ≥3.5 mm (cervical) or ≥4.5 mm (lumbar) suggests instability
- Motion across a fused segment indicates pseudarthrosis
- MRI is preferred over flexion-extension films for acute ligamentous injury evaluation
References¶
- Khan SN, Erickson G, Sena MJ, Gupta MC. Use of flexion and extension radiographs of the cervical spine to rule out acute instability in patients with negative computed tomography scans. J Orthop Trauma. 2011;25(1):51-56. PMID: 21085024. Available from: https://pubmed.ncbi.nlm.nih.gov/21085024/
- Insko EK, Gracias VH, Gupta R, Goettler CE, Gaieski DF, Dalinka MK. Utility of flexion and extension radiographs of the cervical spine in the acute evaluation of blunt trauma. J Trauma. 2002;53(3):426-429. PMID: 12352475. Available from: https://pubmed.ncbi.nlm.nih.gov/12352475/
- Alvarez AP, Anderson A, Farhan SD, Lu Y, Lee YP, Oh M, et al. The utility of flexion-extension radiographs in degenerative cervical spondylolisthesis. Clin Spine Surg. 2022;35(7):319-322. PMID: 35276718. PMCID: PMC9311460. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC9311460/
- Chan V, Marro A, Rempel J, Nataraj A. Determination of dynamic instability in lumbar spondylolisthesis using flexion and extension standing radiographs versus neutral standing radiograph and supine MRI. J Neurosurg Spine. 2019;31(2):229-235. PMID: 31026815. Available from: https://pubmed.ncbi.nlm.nih.gov/31026815/
- Wu SK, Kuo LC, Lan HCH, Tsai SW, Chen CL, Su FC. The quantitative measurements of the intervertebral angulation and translation during cervical flexion and extension. Eur Spine J. 2007;16(9):1435-1444. PMID: 17464516. PMCID: PMC2200749. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC2200749/
- Dvořák J, Panjabi MM, Chang DG, Theiler R, Grob D. Functional radiographic diagnosis of the lumbar spine: flexion-extension and lateral bending. Spine (Phila Pa 1976). 1991;16(5):562-571. PMID: 2052999. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC8009657/
- Gaillard F, et al. Lumbar spine (flexion and extension views). Radiopaedia.org. Available from: https://radiopaedia.org/articles/lumbar-spine-flexion-and-extension-views