What Imaging Do Orthopaedic Surgeons Need for Pre-Operative Planning?
Pre-operative planning imaging must show the full mechanical axis of both limbs under physiological load, with calibrated measurements accurate enough for implant templating. Standing, weight-bearing EOS imaging captures the entire lower limb, pelvis and spine on a single exposure, with inherent 1:1 scale and DICOM-ready output, giving surgeons the data they need without magnification error.
Key takeaways
- Standing EOS captures both limbs and the pelvis on one calibrated image, at 1:1 scale.
- Inherent calibration removes the magnification error associated with conventional radiographs.
- About 90% less radiation than a standard X-ray, around ten times less.
- Images are delivered as DICOM files compatible with your templating software.
- Fast referral pathway from register to refer patients to image delivery.
Why does pre-operative imaging need to be weight-bearing?
Alignment under load is the only alignment that matters in surgery. When a patient lies down for a conventional radiograph, CT or MRI, gravity is removed and the muscles relax. Joint spaces open, rotational deformities reduce, and the mechanical axis shifts. The image may understate the very deformity you are planning to correct.
Standing, weight-bearing imaging captures the skeleton in the position it actually functions. Leg-length discrepancy, varus or valgus malalignment, pelvic obliquity, and sagittal balance all present as they do in life. For pre-operative planning imaging, this is the difference between templating on a best guess and templating on reality.
What does standing EOS imaging provide for surgical planning?
EOS provides a single, calibrated, full-length radiographic image of the patient standing upright. Both limbs, the pelvis and the spine are captured simultaneously. The slot-scanning technology produces images at a true 1:1 ratio, so there is no magnification error and no need for an external calibration marker.
No magnification error. No ball marker needed. Measurements reflect true anatomy.
Images delivered via DICOM transfer, ready for your templating software and PACS.
About 90% less radiation than a standard X-ray, around ten times less.
Full bilateral capture from hip to ankle. No stitching artefacts or alignment errors.
The result is an image you can template directly, with confidence that the measurements for implant sizing, offset, and component position reflect the patient's true standing anatomy.
How does EOS compare with conventional pre-operative imaging?
EOS addresses several well-documented limitations of conventional radiography and CT for surgical planning imaging. The table below summarises the key differences.
| Factor | Conventional X-ray | CT scanogram | Standing EOS |
|---|---|---|---|
| Patient position | Supine or standing (single region) | Supine | Standing, weight-bearing |
| Field of view | Single joint or stitched cassettes | Full leg, supine only | Both limbs, pelvis and spine in one exposure |
| Magnification | Variable, requires calibration marker | Minimal | 1:1 scale, inherently calibrated |
| Calibration marker needed | Yes | No | No |
| Radiation dose | Standard | Higher | About 90% less than standard X-ray |
| Stitching artefacts | Possible with multi-cassette | None | None |
| DICOM output | Usually | Yes | Yes |
A note on MRI. EOS shows bones, joints and alignment with excellent detail. For soft-tissue assessment, disc pathology or nerve compression, MRI is usually the better tool. Many surgical plans benefit from both.
How do I refer a patient for standing EOS imaging?
Referral is straightforward. You can register to refer patients through our online portal, or contact us directly at 19 Harley Street, London. No GP letter is required.
Register or refer
Complete the short online form or send us the referral details directly. Specify the clinical question and which regions you need imaged.
Patient attends
Your patient visits ScanAlign, standing EOS imaging in London at 19 Harley Street. The scan itself takes only a few seconds.
Calibrated images produced
Full-length, 1:1-scale images are generated with all relevant alignment measurements.
DICOM transfer
Images are delivered to you via DICOM, ready for import into your PACS and templating software.
Ready to refer? Refer a patient for pre-operative imaging
Which surgical procedures benefit from standing EOS imaging?
Any procedure that depends on accurate limb alignment, leg-length measurement, or implant sizing benefits from calibrated, weight-bearing imaging. Common referral reasons include the following.
The low radiation dose also makes EOS well suited to post-operative follow-up imaging, where repeat scans may be needed over time to monitor component position or alignment change.
Frequently asked questions
No. You can refer directly as a consultant or surgeon. The patient can also self-refer. No GP letter is required.
EOS uses slot-scanning technology with a fixed, known geometry between the X-ray source and the detectors. This produces images at a true 1:1 ratio without the need for an external calibration marker, removing the magnification error that conventional radiographs introduce.
Yes. Images are delivered as standard DICOM files. They can be imported directly into your PACS and are compatible with common templating software.
EOS delivers about 90% less radiation than a standard X-ray, around ten times less. This is particularly relevant when repeat imaging is needed for post-operative monitoring.
Yes. A single standing exposure captures both lower limbs from hip to ankle, along with the pelvis, on one continuous image. There is no need to stitch separate cassettes, so there are no stitching artefacts.
Yes. EOS is well suited to knee replacement planning because it shows the full mechanical axis under standing load. This allows accurate measurement of the HKA angle and confident templating of component sizes without magnification error. See our page on full-leg standing x-ray for more detail.
Yes. Because EOS captures the pelvis and spine in a standing position, it shows functional pelvic tilt under load. This is valuable for planning acetabular component orientation, particularly in patients with spino-pelvic imbalance.
The scan itself takes only a few seconds. The patient stands still inside the EOS system while the image is acquired. The entire appointment is brief.
Not always. EOS excels at showing bony alignment, joint spacing, and mechanical axis under load. For soft-tissue detail, disc pathology, or nerve assessment, MRI remains the better tool. For cross-sectional bone detail, CT has its own role. Many surgical plans use EOS alongside other modalities.
You can register to refer patients through our online referral portal or contact us directly at 19 Harley Street, London.
Give your surgical plan the imaging it deserves
Standing, calibrated, 1:1-scale imaging delivered via DICOM. Register to refer or send us your first patient.
Refer a patient for pre-operative imagingWritten by Abbas Dhami (Specialist Diagnostic Radiographer)
Sources
- Illés, T. & Somoskeöy, S. (2012). The EOS imaging system and its uses in daily orthopaedic practice. International Orthopaedics, 36(7), 1405-1411.
- Deschênes, S. et al. (2010). Diagnostic imaging of spinal deformities: reducing patients' radiation dose with a new slot-scanning X-ray imager. Spine, 35(9), 989-994.
- British Orthopaedic Association. Standards for pre-operative planning and templating in arthroplasty. BOA guidance documents (ongoing).
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.