How Is Femoral Torsion Measured Without a CT Scan?
Femoral anteversion and torsion can be measured accurately with a low dose biplanar EOS scan instead of CT. The EOS system captures two simultaneous standing images and builds a 3D reconstruction of your femur, giving your surgeon the version angle they need with about 90% less radiation than a standard X-ray, around ten times less.
Key takeaways
- Femoral torsion describes how much your thigh bone is twisted along its length.
- CT has been the traditional way to measure it, but it delivers a relatively high radiation dose.
- EOS biplanar imaging produces a 3D model of the whole leg while you stand, using about 90% less radiation than a standard X-ray.
- Standing measurement captures how torsion affects your alignment under real weight-bearing conditions.
- The results can guide decisions about physiotherapy, gait retraining, or surgical planning such as derotation osteotomy.
What is femoral anteversion and why does it matter?
Femoral anteversion is the natural forward twist of your thigh bone (femur) between the hip joint and the knee. Everyone has some degree of this twist. When it falls outside the typical range, clinicians call it excessive anteversion or, if the bone twists the other way, retroversion. You can learn more about the difference between anteversion versus retroversion.
Too much or too little twist changes the way your leg sits in the hip socket. It can cause in-toeing (feet pointing inward when you walk), hip pain during activity, or a restricted range of internal and external hip rotation. Over time, it may contribute to cartilage wear or compensatory problems at the knee or lower back. Understanding femoral anteversion in adults is an important step toward working out why you have ongoing symptoms.
Why is CT the traditional way to measure femoral torsion?
CT has been the standard for measuring femoral version because it creates cross-sectional slices through the hip and knee, allowing the radiologist to calculate the twist angle precisely. It works well for the measurement itself, but it has two significant drawbacks.
First, a CT rotational profile assessment of both legs involves a meaningful dose of ionising radiation targeted at the pelvis and knees. For a measurement that many people need repeated over time, or that younger adults may need before surgery, this adds up.
Second, CT is performed lying down. Your muscles relax, gravity no longer loads your joints, and the image does not reflect how your bones and joints actually line up when you are standing and walking. That is a significant gap when the whole point of the measurement is to understand how torsion affects your movement in real life.
How does EOS measure femoral torsion without CT?
EOS is a biplanar imaging system. It takes a front-facing and a side-facing image at the same time, in a single standing scan lasting about 20 seconds. Specialist software then uses those two views to build a calibrated 3D reconstruction of your skeleton.
From that 3D model, the version angle of each femur can be calculated, along with tibial torsion, knee alignment, and overall leg rotation from hip to ankle. Because you are standing in your natural posture, the measurements reflect real weight-bearing alignment, not a relaxed position on a scanning table.
The radiation dose is about 90% less than a standard X-ray, around ten times less. For a scan that covers both legs from pelvis to feet, that is a considerable difference compared with CT. You can read a detailed breakdown of EOS compared with x-ray, CT and MRI.
How does EOS compare with CT for torsion measurement?
EOS and CT both provide accurate version angles, but they differ in radiation dose, patient position, and the scope of information they deliver in a single scan.
| Factor | CT rotational profile | EOS biplanar scan |
|---|---|---|
| Patient position | Lying down | Standing, weight-bearing |
| Radiation dose | Higher | About 90% less than a standard X-ray |
| 3D reconstruction | Yes (from many slices) | Yes (from two simultaneous views) |
| Full-leg alignment | Not in one scan | Pelvis to feet in one image |
| Tibial torsion | Requires additional slices | Included in the same scan |
| Soft tissue detail | Good | Not applicable (bones and joints only) |
When MRI is the better choice: EOS shows bones, joints, and alignment. If your clinician needs to see soft tissue such as cartilage, labrum, muscles, or nerves, MRI is usually the better tool. The two scans answer different questions and often complement each other.
What are the steps to get a femoral torsion measurement at ScanAlign?
You do not need a GP referral. The process is straightforward, and you can self-refer at any stage.
Free video consultation
A brief call with a specialist radiographer to discuss your symptoms and confirm whether an EOS scan is the right next step for you.
Attend your scan
You stand inside the EOS unit at our Harley Street clinic. The scan takes about 20 seconds and covers both legs from pelvis to feet.
3D reconstruction and analysis
The biplanar images are used to build a 3D model of your lower limbs. Femoral version, tibial torsion, and full rotational profile are all calculated from this model.
Your report
You receive a detailed report covering your rotational profile and alignment findings. This is exactly what a surgeon or physiotherapist needs for planning. Find out more about what an EOS scan report shows.
Who should consider an EOS torsion measurement?
A standing rotational profile assessment is useful for anyone with unexplained hip, knee, or gait problems where torsion may be a factor. It is not the right tool for every situation.
- Persistent in-toeing or out-toeing as an adult
- Hip pain with limited internal or external rotation
- Pre-surgical planning for derotation osteotomy
- Follow-up measurement with lower radiation than CT
- Combined femoral and tibial torsion assessment needed
- Soft tissue injury (labral tear, muscle strain). MRI is better.
- Acute fracture or trauma. A&E or urgent imaging is needed first.
- Infection or tumour concern. CT or MRI with contrast is more appropriate.
Not sure whether an EOS scan is right for your situation? Start with a free video consultation. A specialist radiographer will talk through your symptoms and advise you honestly.
Book a free video consultationFrequently asked questions
Femoral anteversion is the forward twist of your thigh bone between the hip and the knee. A certain amount is normal. When the angle is unusually large or small, it can affect hip rotation, walking pattern, and joint comfort.
Traditionally it is measured with a CT scan that takes cross-sectional images of the hip and knee. EOS biplanar imaging offers an alternative. It builds a 3D model from two standing views, allowing the version angle to be calculated with significantly less radiation.
Published research shows strong agreement between EOS 3D reconstructions and CT-based measurements for femoral version. Your clinician can discuss whether EOS is suitable for your specific clinical question.
An EOS scan uses about 90% less radiation than a standard X-ray, around ten times less. This is particularly relevant for full-leg scans covering the pelvis, thighs, and knees.
Yes. Because EOS captures the full leg from pelvis to feet in one standing scan, both femoral version and tibial torsion measurement are included in the same 3D reconstruction.
No. You can self-refer. We recommend starting with a free video consultation so a specialist radiographer can confirm that EOS is the right scan for your needs.
You can book a torsion measurement scan through our online booking page, where up-to-date pricing is provided during the booking process.
When you lie down, muscles relax and gravity no longer loads your joints. Standing imaging captures how torsion, alignment, and rotation interact under the same forces your body experiences every day. This gives a more clinically relevant picture.
Yes. The 3D rotational profile from an EOS scan provides the precise version angles a surgeon needs to plan a derotation osteotomy. Many surgeons now accept EOS data as an alternative to CT for this purpose.
ScanAlign is based at 19 Harley Street, London. We are a private, self-pay clinic offering ScanAlign, low dose standing imaging for whole-body alignment assessment.
Get your torsion measured with less radiation
A free video consultation is the first step. We will tell you honestly whether an EOS scan is the right choice for your situation.
Book a free video consultationWritten by Abbas Dhami (Specialist Diagnostic Radiographer)
Sources
- Guenoun B, et al. Reliability of a new method for lower-extremity measurements based on stereoradiographic three-dimensional reconstruction. Orthopaedics & Traumatology: Surgery & Research, 2012;98(5):506-513.
- Buck FM, et al. Femoral and tibial torsion measurements with 3D models based on low-dose biplanar radiographs in comparison with standard CT measurements. American Journal of Roentgenology, 2012;199(5):W607-W612.
- EOS imaging clinical evidence library. EOS imaging (now part of Alphatec Holdings). Available at: eos-imaging.com.
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.