How the trim line is currently generated.

Limbform takes a 3D scan of a transtibial residual limb and produces a trim curve and a manufacturing file. The steps below run offline on a small computer beside the scanner. The prosthetist makes the clinical decisions at each step.

Steps

The residual limb is captured with a commercial handheld scanner. STL, PLY and OBJ meshes load directly. The software cleans the mesh and rotates it into a standard orientation, so later steps do not depend on how the scanner was held.
The prosthetist marks about seven anatomical landmarks on the scan: patella, patellar tendon, tibial tubercle, fibular head, medial and lateral condyles, and the popliteal area. Each pick snaps to the nearest point on the surface. The landmark set is saved next to the scan to ensure a case reopens as it was left.
A rule engine draws the trim curve from the landmarks. The rules set the relief over the patellar tendon, the height of the posterior wall and how smoothly the curve passes through the medial and lateral walls. The software then checks that the curve is a closed loop, lies on the surface and does not cross itself.
The curve and the limb are exported as STEP for CAD/CAM or STL for printing.

Hardware

The scanner is currently a commercial handheld unit. The pipeline only runs on a Jetson Orin Nano Super module beside it.

Output on a synthetic limb

Rendered tapered limb model with the proximal end up. A red trim curve wraps the upper third and two blue landmark markers just below it. — Pipeline output on a synthetic test limb: the red curve is the generated trim line and the blue markers are placed landmarks.

The next image on this page will come from a scan of a volunteer limb or a phantom, and a short video of the full offline run on the module will follow it.

Files from the run shown above:

synthetic-trimline.step, the trim curve as 180 points (17 KB)
synthetic-limb.stl, the synthetic limb mesh (250 KB)

Curve checks on the synthetic limb with the default rules
Check	Result
Gap from the last point back to the first (equal to the point spacing)	1.59 mm
Largest distance from the surface	0.04 mm
Self-intersections	0

What is not done yet

Loading, cleanup, orientation, landmarks, curve generation, curve checks and export all work on synthetic geometry. The default rule values are 15 mm of anterior relief, 10 mm of posterior rise and a smoothing factor of 0.3. These are only starting values which will change once prosthetists review curves on real scans. The pipeline has not been validated on patient scans and is not a medical device.

If you fit transtibial sockets and want to review generated curves on your own scans, use the pilot form.