How Does Sagittal Balance Imaging Support Spinal Surgery Planning?
Standing, weight-bearing sagittal balance imaging captures the full spine and pelvis in a single unstitched radiograph under physiological load. This gives spinal surgeons accurate spinopelvic parameters, reveals compensation mechanisms that disappear when the patient lies down, and supports precise deformity correction planning and post-operative comparison.
Key takeaways
- EOS produces a single, unstitched full spine standing radiograph from C2 to the femoral heads, with about 90% less radiation than a standard X-ray.
- Weight-bearing images reveal the true sagittal vertical axis (SVA) and compensation mechanisms such as pelvic retroversion and knee flexion.
- Spinopelvic parameters including pelvic incidence, lumbar lordosis and PI-LL mismatch are measured under physiological load.
- Low dose allows serial imaging for pre-operative planning and post-operative comparison without cumulative radiation concerns.
- EOS shows bony alignment. For soft tissue, discs or nerve assessment, MRI remains the appropriate tool.
Accurate sagittal balance assessment is fundamental to adult deformity surgery planning. The surgical literature consistently links sagittal malalignment to poor patient-reported outcomes, and correction targets are derived from standing spinopelvic measurements. Yet many referral pathways still rely on supine or segmented imaging, which can understate the degree of imbalance the patient actually experiences on their feet.
At ScanAlign, unstitched full-body standing imaging at 19 Harley Street, we provide EOS slot-scanning radiography specifically designed for this clinical need. The system captures the entire skeletal chain, from the skull base to below the knees, in a single, calibrated, weight-bearing acquisition.
Why does standing imaging change spinal surgery planning?
Standing imaging reveals the spine under its true mechanical load, which is the only position that reflects the patient's functional alignment. When a patient lies supine, muscular relaxation, the absence of gravity and the support of the table can mask significant sagittal imbalance. Curves flatten, pelvic tilt reduces, and the C7 plumb line shifts posteriorly. The result is a radiograph that may underestimate the correction needed.
A full spine standing radiograph with EOS removes these artefacts. The patient stands naturally, bearing weight through their usual compensation strategies. If the pelvis is retroverted, the hips are flexed or the knees are bent to maintain gaze, all of this is visible in a single image. This is the functional reality the surgeon must correct for.
Which spinopelvic parameters can be measured from a standing EOS scan?
All standard spinopelvic parameters used in adult deformity planning can be derived from a calibrated standing EOS acquisition. These include pelvic incidence (PI), lumbar lordosis (LL), PI-LL mismatch, sacral slope, pelvic tilt, thoracic kyphosis, the sagittal vertical axis (SVA) and the C7 plumb line relative to the sacral endplate.
The horizontal offset of C7 from the posterior sacral endplate, measured under true weight-bearing conditions.
The difference between pelvic incidence and lumbar lordosis, a core planning metric for lordosis restoration targets.
Weight-bearing pelvic tilt reveals active compensation. Supine values may differ significantly from standing values.
Full-length imaging captures thoracic kyphosis, cervical lordosis and coronal alignment simultaneously.
Because EOS captures the entire skeletal chain in a single unstitched exposure, there are no stitching artefacts that can distort angular measurements. The image is geometrically calibrated, which supports reliable measurement software output.
How do standing and supine imaging compare for deformity assessment?
Standing imaging consistently reveals greater sagittal imbalance than supine imaging in the same patient. The difference is clinically meaningful and can change surgical targets.
True physiological load. The patient stands with their natural posture, including any compensatory strategies. The SVA, pelvic tilt and knee flexion are all visible. The C7 plumb line position reflects the functional offset the patient lives with.
Unstitched, calibrated acquisition. A single pass from head to below the knees captures the full chain without stitching error. The low-dose slot-scanning technology delivers about 90% less radiation than a standard X-ray, around ten times less, making serial imaging practical for pre-operative and post-operative comparison.
Gravity is removed. The table supports the spine, relaxing paraspinal muscles and reducing curves. Pelvic tilt often decreases. The SVA shifts posteriorly, masking the degree of forward imbalance. In patients with flatback syndrome or fixed sagittal imbalance, supine films may appear deceptively normal.
Compensation is hidden. Pelvic retroversion, hip extension and knee flexion are not visible on a supine film. These compensatory mechanisms are critical to understanding how much correction is required and where the correction should be placed.
For adult deformity surgery planning, the difference between standing and supine spinopelvic measurements can exceed clinical thresholds. Surgical targets derived from supine data risk under-correction, which the literature associates with revision surgery and poor outcomes.
How do surgeons refer patients for standing sagittal balance imaging?
Surgeons can refer patients directly to ScanAlign for EOS sagittal balance imaging. No GP involvement is needed. The process is straightforward and designed for the surgical workflow.
Register as a referrer
Complete a short registration so we can link referrals to your practice. You can register to refer patients online.
Submit a referral
Send us the clinical indication and any specific imaging requirements. We accommodate requests for particular views, field of view or inclusion of the lower limbs.
Patient attends for imaging
The scan takes place at our Harley Street clinic. The acquisition itself typically lasts under a minute. The patient stands in their natural posture throughout.
Images and measurements delivered
Calibrated DICOM images are provided along with spinopelvic parameter measurements. These are compatible with standard deformity planning software.
If you are a spinal surgeon or clinical team member and would like to discuss imaging requirements, you can refer a patient or contact us directly.
Book a free video consultationWhen is MRI more appropriate than EOS for spinal assessment?
MRI is usually the better tool when the clinical question involves soft tissue, discs or nerves. EOS shows bones, joints and alignment with precision under weight-bearing conditions, but it does not image the spinal cord, disc hydration, neural foramina or ligamentous structures.
EOS and MRI are complementary. EOS provides the global alignment and spinopelvic parameter data needed for deformity correction planning. MRI provides the soft-tissue detail needed for neural decompression planning and disc assessment. In most adult deformity cases, both modalities contribute to the surgical plan.
Frequently asked questions about sagittal balance imaging
Sagittal balance imaging is a standing, weight-bearing radiograph that captures the entire spine and pelvis in the sagittal plane. It allows measurement of the key spinopelvic parameters used to assess and plan correction of sagittal malalignment.
The sagittal vertical axis reflects the patient's functional balance under gravity. When the patient lies down, gravity is removed, muscles relax, and the SVA shifts posteriorly. Standing measurement captures the true offset and any compensation mechanisms the patient uses.
EOS uses slot-scanning technology to produce a single, unstitched, calibrated image from head to feet. Conventional full-length standing X-rays are typically stitched from multiple cassettes, which can introduce measurement error. EOS also delivers about 90% less radiation than a standard X-ray, around ten times less.
Yes. The calibrated EOS image includes the pelvis and full lumbar spine, allowing accurate measurement of both pelvic incidence and lumbar lordosis. The PI-LL mismatch is calculated from these values.
EOS delivers about 90% less radiation than a standard X-ray, around ten times less. This low dose makes it practical for serial pre-operative planning and post-operative comparison imaging without the cumulative radiation concerns associated with conventional radiography or CT.
No. Consultant surgeons can refer patients directly. Patients may also self-refer. There is no requirement for GP involvement.
Common indications include adult spinal deformity assessment, flatback syndrome, degenerative sagittal imbalance, pre-operative planning for corrective osteotomy or long fusion, post-operative alignment monitoring, and assessment of adjacent segment disease following previous surgery.
Yes. EOS images are delivered as calibrated DICOM files. They are compatible with standard surgical planning software used for adult deformity correction, including tools that calculate correction targets from spinopelvic parameters.
The acquisition itself typically lasts under a minute. The patient stands still in their natural posture while the scanner moves from head to feet. The total appointment, including positioning, is brief.
ScanAlign is a private, self-pay clinic. For current pricing and what is included, please see our frequently asked questions page.
Refer a patient for standing sagittal balance imaging
If you would like to discuss a case or refer a patient for EOS imaging at our Harley Street clinic, we are happy to help.
Book a free video consultationWritten by Abbas Dhami (Specialist Diagnostic Radiographer)
Sources
- Schwab F, Ungar B, Blondel B, et al. Scoliosis Research Society-Schwab adult spinal deformity classification: a validation study. Spine. 2012;37(12):1077-1082.
- Lazennec JY, Brusson A, Rousseau MA. Lumbar-pelvic-femoral balance on sitting and standing lateral radiographs. Orthopaedics & Traumatology: Surgery & Research. 2013;99(1 Suppl):S87-S103.
- Deschênes S, Charron G, Beaudoin G, et al. Diagnostic imaging of spinal deformities: reducing patients radiation dose with a new slot-scanning X-ray imager. Spine. 2010;35(9):989-994.
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.