Analysis of CT-scan based hip with generic motion data

[Olesya Klets]

Hello everyone,

A bit of background:

I would like to analyse hip moments and moment arms during gait for analysis if hip implant (testing different locations of the hip implant and how it affects hip muscles' moments and moment arms, hip joint reaction forces). I will use motion capture data from the OpenSim (so it is not subject-specific).

I have three stl files: right femur, left femur, pelvis. The rest of bones will be from OpenSim. I will scale them by one factor-these generic bones and try to apply this motion capture data from OpenSim. Is it doable in OpenSim?

My question is about first steps. I used ParaView and found what translations and rotations should be applied to my bones and that bones should by scaled by factor 0.001.

I have copied stl files to Geometry folder in OpenSim. I edited gait2392 simbody.osim in text editor and added translations, rotations, scale factor. When I open this model again in OpenSim, bones are missing.

I have no idea what I am doing wrong and would be grateful for help. I have read tutorials but didn't find a relevant info. Would be grateful for any advice.

I will add the screenshot of a part of the .osim code for one femur.

Thank you in advance for help!

[Dimitar Stanev]

Hi,

It is possible that the stl files are stored in millimeters. OpenSim uses meters and this means that if you import a geometry that is in mm then the vertices are very far away (e.g., 1000mm is interpreted as 1000m). To check this look at the values of the vertices in paraviw. If they are in the range of hundreds then you have to scale your geometry by a factor of 1 / 1000 before importing into OpenSim.