Rajagopal's model - Patella Movement

[Axel Koussou]

Dear OpenSim experts,

I am using the Rajagopal's model and I would like to have some info about the patella movement.
I understand that the knee_angle_r/l_beta coordinate, which is the coordinate related to the movement of the patella, depends on the knee angle.

If you run a IK analysis or you look at the IK results provided in the Rajagopal's model download forlder (https://simtk.org/projects/full_body/. Go to IK folder, then results_walk or run folder), you can easily compute that the knee_angler/l_beta obtained is the knee angle multiplied by around 0.0175.

Nevertheless, if you look into the.osim model file, in the ConstraintSet section, you will find the constraint about the patella movement : the knee_angle_r/l_beta coordinate is related to the knee angle with a linear function, whom coefficient is 1.

So, why is it not 0.0175?

Moreover, I would like yto study the knee in hyper-extension. The knee RoM of the model was originally limited to 0 degrees of extension. Thus, I increased the RoM allowed, and I would like to be sure of the patella movement in this added extension degrees.
The patella movement is related to the knee_angle_r/l_beta through a SimmSpline function. Does anybody have information about this function. In the article, it is said that :

Similarly, patellar kinematics were parameterized by the knee flexion angle using the kinematics define in Arnold et al., modified such that the patella articulated with the femur.

However, I did not find any information in the article quoted.

Thanks in advance,

Regards

P.S : I have already sent an email to the authors of the model but I did not receive any answer.