knee_angle_l_beta explanation

[Sergiu Iliev]

hi all,

I am new to OpenSim and have started processing some data to simulate lower body dynamics. I am particularly interested in the knee joint.

I have used the Rajagopal model. As far as I know, the knee is modeled as a 1D joint that is constrained to allow only flexion and extension. However, in the inverse kinematics results I can see a knee_angle_l_beta value. What does this mean, where can I find more information about it and how is it computed?

I'm curious to hear your advice and I thank you in advance!

Best,
Sergiu

[Dimitar Stanev]

Hi Sergiu,

This coordinate is related to the movement of the patella. If you look into the .osim file and locate this coordinate, you will see that it is actually a coupled coordinate that is a function of the actual knee angle, therefore not a free degree of freedom. Please also note that the knee is not modeled as a pure rotation joint, but it also translates in the anterior-posterior and inferior-superior directions. These translations are also a function of the knee angle. Some links that might help you:

https://simtk-confluence.stanford.edu:8 ... Sim+Models
https://simtk-confluence.stanford.edu/d ... 4%2BModels
https://simtk-confluence.stanford.edu:8 ... Model+2010

[Sergiu Iliev]

Thank you Dimitar for the quick reply and explanation - that is very helpful and much appreciated!