What Imaging Does a Surgeon Need to Plan a Hip Replacement?
Your surgeon needs a calibrated, weight-bearing x-ray of the whole pelvis and both hips to plan a hip replacement accurately. Standing imaging reveals your true pelvic tilt, leg length difference and joint alignment under load, which all affect implant sizing, cup positioning and the overall surgical plan.
Key takeaways
- Surgeons rely on calibrated x-rays to template the correct implant size and position.
- Lying-down images can hide pelvic tilt, making cup angle and leg length measurements less reliable.
- A standing, whole-body image captures the pelvis and spine together, giving a full picture of your alignment.
- An EOS standing x-ray produces a non-magnified, life-size image at about 90% less radiation than a standard x-ray.
- No GP referral is needed for a private pre-operative scan.
What x-rays does a surgeon need before a hip replacement?
A surgeon needs at least an anteroposterior (front-on) x-ray of the full pelvis and a lateral (side-on) view of the affected hip. These images are used for surgical templating, which means digitally overlaying implant outlines onto your x-ray to choose the best size and position for the replacement components.
For templating to work, the image must be calibrated. That means the x-ray includes a metal ball of a known size placed beside your hip, so the software can correct for any magnification. If magnification is not accounted for, implant sizing can be wrong by a clinically significant amount.
The key measurements your surgeon takes from these images include:
- Implant size. The femoral stem and acetabular cup must fit your anatomy precisely.
- Cup angle. The angle at which the socket component is placed affects stability and wear.
- Offset. The distance from the centre of the hip to the femur's shaft, which controls muscle tension and gait.
- Leg length. Your surgeon plans to restore equal leg lengths, so an accurate baseline is essential.
Why does standing imaging matter for hip replacement planning?
Standing imaging matters because your pelvis tilts differently when you are upright and bearing weight compared with lying down. When you lie on an x-ray table, your muscles relax, your pelvis falls into a neutral position and the image may not reflect the alignment you actually live with.
Pelvic tilt has a direct effect on the angle of the acetabular cup. A cup that looks well-positioned on a lying-down image can be too steep or too flat once you stand up. This is part of a broader assessment called spinopelvic analysis, which looks at how your spine and pelvis work together.
Shows your real, weight-bearing alignment. Your pelvic tilt, any leg length difference and the natural curve of your spine are all captured as they are in everyday life. The image is produced at true life size with no magnification error, removing the need to guess a correction factor.
Muscles relax. Alignment shifts. With no gravity loading the joint, the pelvis can tilt forward or backward compared with standing. Magnification varies depending on your body size and the distance from the x-ray source, which means the calibration marker may not perfectly match the plane of your hip joint.
If you have a stiff or fused spine, your pelvis compensates more than usual when you move between sitting and standing. A standing image makes that compensation visible, giving your surgeon the information needed to position the cup safely. Conditions like developmental dysplasia of the hip or unusual hip anteversion and retroversion also benefit from this fuller picture.
What is included in a pre-operative hip replacement scan?
A pre-operative hip imaging session at ScanAlign, private standing imaging in London, includes everything your surgeon needs for templating and alignment assessment. For full details of our service, see our hip replacement imaging service.
A head-to-foot or pelvis-to-ankle image captured while you stand naturally.
No calibration ball needed. The image is produced at a 1:1 scale, removing magnification error.
Pelvic tilt, sacral slope and spinal balance are all visible on the same image.
A specialist radiographer's report with images formatted for surgical templating software.
How does an EOS standing x-ray compare with a standard hip x-ray?
An EOS standing x-ray captures the full skeleton in one pass while you stand upright. Below is a quick comparison with a conventional hospital x-ray for hip replacement planning.
| Feature | Standard x-ray | EOS standing x-ray |
|---|---|---|
| Patient position | Usually lying down | Standing, weight-bearing |
| Magnification | Present. Needs calibration ball | Non-magnified, true 1:1 scale |
| Pelvic tilt visible | Not under real-world loading | Yes, under natural weight-bearing |
| Radiation dose | Standard | About 90% less, around ten times less |
| Full spine included | Separate image required | Captured in the same scan |
How do I book pre-operative imaging before a hip replacement?
You do not need a GP referral. You can self-refer or bring a request from your orthopaedic surgeon.
Free video consultation
A short call to discuss your surgery timeline and confirm the scan is right for you.
Attend 19 Harley Street
The scan itself takes only a few minutes. You stand still in normal clothing (no metal). No preparation is needed.
Images reviewed
A specialist radiographer reviews your images and prepares a report with templating-ready files.
Sent to your surgeon
The report and images are shared with your surgical team, ready for their planning session.
Ready to get the imaging your surgeon needs? You can book pre-operative hip imaging or start with a free consultation.
Book a free video consultationIs an EOS scan safe before hip replacement surgery?
Yes. An EOS scan uses about 90% less radiation than a standard x-ray, around ten times less. It is a quick, non-invasive procedure with no injections and no contrast dye. You simply stand in the scanner for a few seconds.
When is MRI better? EOS shows bones, joints and alignment clearly. If your surgeon also needs to assess soft tissue, cartilage, tendons or nerves around the hip, MRI is usually the better tool. Many patients benefit from both.
Frequently asked questions
You need a calibrated anteroposterior x-ray of the full pelvis and a lateral view of the affected hip. A standing, non-magnified image is the most accurate option for surgical templating because it shows your true pelvic tilt and leg length under load.
No. You can self-refer for a private scan. You are also welcome to bring a referral from your orthopaedic surgeon if you have one.
Pelvic tilt changes the effective angle of the acetabular cup once the implant is in place. If the surgeon plans on a lying-down image where the pelvis is in a different position, the cup angle may not be optimal when you stand up. Standing imaging shows your real tilt.
A non-magnified x-ray produces images at true life size. Standard x-rays enlarge the image slightly because of how the beam spreads. A non-magnified image removes that error, so implant templates can be overlaid directly without correction factors.
An EOS scan uses about 90% less radiation than a standard x-ray, around ten times less. This is especially helpful if multiple images are needed during your surgical planning.
Yes. EOS images are provided in standard DICOM format and are compatible with common digital templating systems. Because they are already at 1:1 scale, no magnification calibration step is needed.
The scan itself takes only a few minutes. You stand still inside the EOS system while it captures a full image in a single pass. Most appointments, including paperwork, are short and straightforward.
Wear comfortable clothing without metal fastenings (zips, buttons, underwire). Most people can be scanned in light gym-style clothing. You will be asked to remove belts, jewellery and anything metallic around the scan area.
Pricing depends on the scan protocol your surgeon requires. You can discuss this during your free video consultation. Full cost information is available on the ScanAlign website.
Yes, and it is especially valuable. A stiff or fused spine limits how much your pelvis can tilt between sitting and standing. A standing image captures your actual pelvic position, which helps your surgeon choose a safer cup angle.
Get the imaging your surgeon needs
A standing, non-magnified image gives your surgical team the most accurate starting point for a hip replacement. Start with a free video consultation.
Book a free video consultationSources
- Lum ZC, Coury JG, Cohen JL, Dorr LD. The current knowledge on spinopelvic mobility. The Journal of Arthroplasty. 2018;33(1):291-296. (PubMed)
- Illés T, Somoskeöy S. The EOS imaging system and its uses in daily orthopaedic practice. International Orthopaedics. 2012;36(7):1405-1411.
- National Institute for Health and Care Excellence (NICE). Joint replacement (primary): hip, knee and shoulder. NICE guideline [NG157]. 2020.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
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.