Case study

X-ray to 3D CT Reconstruction & Knee Alignment Analytics

CT scans cost several times more than X-rays, which can delay orthopedic diagnosis. A US hospital needed 3D, CT-like results from standard 2D X-rays to measure the bone alignment angles used in surgical planning.
  • Client: Hospital based in the US
  • Industry: Health & Fitness
  • AI capability: Computer Vision
Standing long-leg X-rays annotated with the femoral and tibial mechanical axes, and a knee close-up marking the LDFA and MPTA angles
Bone geometry estimated from standard X-rays
2D → 3D
Plus mHKAA, LDFA and MPTA calculated automatically
CPAK
Cloud deployment for clinical access
AWS
Delivered for a hospital in the US
2024

The challenge

3D answers from a flat image

Assessing lower limb alignment usually calls for 3D imaging. X-rays are cheaper and easier to get, but they lack the volumetric depth of a CT scan. Turning a 2D X-ray into a 3D reconstruction precise enough for clinical screening is hard.

The system had to find and measure bone angles such as the lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) as an initial screening tool. It needed to work across varied patient anatomy with approximately 75–80% accuracy, which called for a specialised deep learning approach.

  • 2D to 3D mapping

    Estimating the shape and depth of bones from a single flat projection.
  • Reconstruction precision

    3D estimates reliable enough for screening, at approximately 75–80% accuracy.
  • Anatomical variability

    Results that hold up across different patients' knee structures and conditions.
  • Cost versus quality

    Useful 3D insight from low-cost X-ray imaging, before a CT is ordered.

What we built

A deep learning pipeline from X-ray to alignment angles

We built the pipeline around 2D to 3D image registration and generative reconstruction. Trained on paired medical data, it predicts 3D bone geometry from flat projections, then an analytics layer takes the orthopedic measurements.

  1. Stage 1

    Take a standard X-ray as input

    The system starts from a regular 2D X-ray, so no extra imaging is needed for the initial evaluation.
    2D X-ray image
  2. Stage 2

    Segment bones and find landmarks

    Automated bone segmentation locates key anatomical landmarks, including the femoral condyles and the functional flexion-extension (F/E) axis.
    Landmarks and surgical axesBone segmentationLandmark detection
  3. Stage 3

    Reconstruct the 3D bone structure

    A neural network trained with Generative Adversarial Networks (GANs) estimates 3D bone geometry from the 2D input, with training focused on keeping the anatomy realistic.
    Estimated 3D bone geometry2D to 3D registrationGANs
  4. Stage 4

    Calculate alignment angles

    An analytics engine calculates CPAK, mHKAA, LDFA and MPTA automatically, and overlays the results on the image for review.
    Standardised angle measurementsCPAKmHKAALDFAMPTA
  5. Stage 5

    Serve it from the cloud

    The deep learning pipeline runs on AWS so results come back quickly and the system scales as more images come in.
    Fast turnaround for cliniciansAWS
long-leg-ap-sample.png
Processing
R · AP standing

Input image

Modality
2D X-ray
View
Standing, hip to ankle
Extra imaging
None

A CT scan would give 3D detail, but costs several times more than an X-ray.

1/4Input is a standard 2D X-ray of the leg: cheaper and more widely available than a CT scan.

Illustrative sample: the leg is a drawing and the angle values are examples, not patient data.

Results and impact

3D-assisted screening at the cost of an X-ray

The system gives clinicians a tool for initial orthopedic screening. Automating the angle calculations supports surgeons in the early stages of preoperative planning and patient evaluation, before more expensive imaging is needed.

  • 3D-assisted insight from a standard X-ray
  • Alignment angles measured the same way every time
  • A simpler first step in the clinical workflow
  • Lower cost of early evaluation

    Initial screening starts from an X-ray instead of a CT scan.
  • Consistent measurements

    CPAK, mHKAA, LDFA and MPTA are calculated automatically rather than by hand.
  • Faster preoperative planning

    Surgeons get alignment data early, while deciding next steps.
  • Built on custom computer vision

    Segmentation, landmark detection and reconstruction models trained for this task.
    Computer vision model training

Project showcase

Angle calculation in action

A recording of the system calculating leg alignment angles, including an initial mHKAA and CPAK assessment.

Demonstrating an initial mHKAA and CPAK assessment.

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