Why Should You Have Your Leg Alignment Checked Before a Knee Replacement?
Because your knee does not work in isolation. A standing, full-leg standing x-ray captures the true alignment from hip to ankle under your body weight. This gives your surgeon calibrated measurements for implant size, position and angle, helping to plan a knee replacement that suits your whole leg, not just the joint itself.
Key takeaways
- Lying-down images can hide the real angle of your leg because gravity is removed.
- A standing scan shows both legs side by side, so your surgeon can compare and plan accurately.
- EOS imaging uses about 90% less radiation than a standard x-ray, around ten times less.
- Calibrated, life-size images allow precise implant templating before you reach the operating theatre.
- No referral is needed. You can self-refer and share the results with your surgical team.
Why does leg alignment matter for knee replacement planning?
Leg alignment matters because your implant needs to sit at the correct angle relative to your entire limb, not just the worn joint surface. If your leg bows inward or outward, a standard knee-only x-ray may not reveal the full picture. Your surgeon needs to see the mechanical axis, the imaginary line from the centre of your hip to the centre of your ankle, to decide exactly where and how to position the new joint.
When you lie down for a conventional x-ray or CT scan, gravity is no longer compressing your joints. Your muscles relax. The image can make alignment look different from how your leg actually loads when you walk. A standing scan captures your leg exactly as it functions in real life.
This is why many orthopaedic surgeons now request a full-leg standing image before surgery. It shows both legs together, so the surgical team can compare the affected side with the unaffected side and plan the correction with confidence.
What is included in a pre-operative alignment assessment?
A pre-operative alignment assessment at ScanAlign, standing EOS imaging in Harley Street includes everything your surgeon needs for accurate knee replacement planning.
Both legs captured hip to ankle in a single exposure while you stand naturally.
Life-size, distortion-free images that allow precise implant templating and sizing.
About 90% less radiation than a standard x-ray, around ten times less.
A detailed report you can share directly with your surgeon or surgical team.
Because the EOS system captures both legs in a single standing exposure, your surgeon can compare the operated side with your other leg. This side-by-side view helps inform decisions about whether a total or partial knee replacement is more appropriate, and supports teams using robotic knee replacement systems that rely on precise pre-operative data.
How do you book a pre-operative knee scan?
You can self-refer without a GP letter or consultant request. Here is how it works.
Free video consultation
A short call with our specialist radiographer to confirm standing imaging is right for your situation and answer any questions.
Attend your scan
Visit 19 Harley Street, London. The scan itself takes only a few seconds while you stand still. Find out more about what happens during an EOS scan.
Receive your report
Your calibrated images and alignment report are prepared and sent to you securely.
Share with your surgeon
Forward the report to your surgical team so they can use it for implant templating and pre-operative planning.
Ready to give your surgeon the full picture before surgery?
Book a free video consultationHow does a standing EOS scan compare to a standard pre-op x-ray?
A standard pre-op x-ray usually captures just the knee joint, often while you are lying down. An EOS standing scan captures both full legs under load. Here is a quick comparison.
| Feature | Standard knee x-ray | EOS standing scan |
|---|---|---|
| Area captured | Knee joint only | Hip to ankle, both legs |
| Patient position | Often lying down | Standing, weight-bearing |
| Mechanical axis visible | No | Yes |
| Calibrated for templating | Varies | Yes, life-size images |
| Both legs compared | Separate exposures needed | Single exposure |
| Radiation dose | Standard | About 90% less |
When MRI is the better choice: EOS shows bones, joints and alignment clearly. If your surgeon needs to assess soft tissue, cartilage, ligaments or nerves around the knee, MRI is usually the better tool. The two scans complement each other well.
What questions should you ask before knee replacement surgery?
Preparing the right questions helps you feel more confident going into surgery. Here are some worth raising with your surgeon.
- Has my full leg alignment been measured, or only the knee joint?
- Would a standing, calibrated image change your approach to implant positioning?
- Are you using mechanical alignment or kinematic alignment for my procedure?
- Do you have life-size images for implant templating?
- How does my other leg compare, and will that affect the plan?
If your surgeon has not yet seen a full-leg standing image, you can book pre-operative imaging yourself and share the results with their team.
Frequently asked questions
No. You can self-refer directly. We will send the report to you, and you can share it with your surgeon.
Standing captures how your leg actually loads when you walk. Lying down removes gravity and can make alignment look different from real life, which may affect implant positioning.
EOS uses about 90% less radiation than a standard x-ray, around ten times less. This is particularly helpful when full-leg images are needed.
EOS images are DICOM-standard medical images, the same format used across NHS and private hospitals. Your surgeon can view them in any radiology system.
The scan itself takes only a few seconds. The whole appointment, including positioning and paperwork, is usually straightforward and quick.
Yes. Both legs are captured in a single standing exposure. This lets your surgeon compare the affected side with your other leg.
Yes. Robotic systems rely on accurate pre-operative measurements. A calibrated, standing full-leg image provides the data these systems need for precise implant placement.
You can find current pricing details on our FAQs page. We are happy to discuss costs during your free video consultation.
No. EOS takes flat images similar to an x-ray, but while you stand. It does not produce cross-sectional slices like CT. The key advantage is capturing true weight-bearing alignment with very low radiation.
EOS and MRI serve different purposes. EOS shows bone alignment under load. MRI shows soft tissue, cartilage and ligaments. Many surgeons find having both gives the most complete picture.
Give your surgeon the full picture
A free video consultation confirms whether standing alignment imaging is right for your knee replacement preparation.
Book a free video consultationWritten by Abbas Dhami (Specialist Diagnostic Radiographer)
Sources
- Paley, D. (2002). Principles of Deformity Correction. Springer. Covers mechanical axis assessment and pre-operative planning for lower-limb surgery.
- Illés, T. & Somoskeöy, S. (2012). The EOS imaging system and its uses in daily orthopaedic practice. International Orthopaedics, 36(7), 1405–1411.
- National Joint Registry (NJR) for England, Wales, Northern Ireland and the Isle of Man. Annual reports on knee replacement outcomes and alignment considerations.
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.