problem with knee joint loads too high in result of Inverse Dynamics

[Linjie Wang]

Dear all,

Did Anyone encounter the problem that the knee joint forces in 3 translational directions and moments in 3 directions were too high during the process of inverse dynamics? I used the model, motion track and GRF data from the 4th Knee Grand Challenge. The result of inverse kinematics is fine, but when I checked the result of inverse dynamics, the loads on the knee joint are very huge (e.g. the vertical force goes 100000N but the GRF in the same direction is around 600N). I tried checking the masses and their loaction, GRF locations, or adding the torso and the other leg, but nothing improved. So I wonder if someone help and give me any suggestion how to deal with it.

Thanks a lot!
Linjie

[Yanis AMMOUCHE]

Dear Linjie,

Maybe it is related to the position of the applied GRF, to check if it's ok, you can visualize them with file => preview_experimental data => .mot file.

What was the name of the motion file you use from the Knee challenge ?

Yanis

[Linjie Wang]

Hi, Yanis.

Thanks a lot for your reply.

the motion file I am currently using is the 'jw_ngait_tm_fast1-new' from the treadmill gait trials and the GRF data is the file of corresponding name.

Linjie

[Yanis AMMOUCHE]

Hi

Sorry for my suggestion, I did not see you already checked the GRF. Just in case, the gravity at the beginning is defined downward the y-axis. I think after doing an inverse kinematic analysis, the model will rotate and the z-axis will be the new upward axis, be sure to change the gravity vector in the OpenSim model even if I'm sure you already did.

I will try to do this ID analysis.

PS : For the IK, I have a problem with the TRC file as they said the number of workunits can't be negative. I saw that you already encountered this type of problem, how did you solve it then ?

[Linjie Wang]

try to change the number of PathFileType from 4 to 3 in the trc file, and then the system will automatically upload the starting and ending times in the trc file into the corresponding windows in the interface of IK tool.

I changed the gravity vector already but there might be some problems somewhere else. Anyway, thanks all the same for your suggestion.

Linjie

[Linjie Wang]

sorry, the value should changed from 3 to 4

[Yanis AMMOUCHE]

Sorry but it says that even when I change the pathfile type from 3 to 4. Did you change/suppress something else for these datas ?

[Linjie Wang]

No, I didn't. Maybe you can check if the names of virtual marks are consistent with the ones of experimental marks in trc file. or do you wanna try my trc file?

[Yanis AMMOUCHE]

No it is ok, I manage to see where the problem was.

I did an Inverse dynamics analysis and I'll show you the results of the knee force, is it what you were talking about ?

[Linjie Wang]

Yes! Have you got any idea about the cause of this problem?