SimmSpline Function for Knee joint translation

[Hooman Shirzadi]

Hello,

I have a question regarding the function that OpenSim has utilized to define the translation of the knee joint having a knee flexion angle. I assume that the developers considered the equations from "Walker et al." paper (please find attached) to define the knee coordinate system. However, I put the flexion angles provided at the XML. file (gait2392) in the equations and did not get the same results for the translation in X and Y axis. Thereby, I would highly appreciate it, if you could provide me the equations that developers already used to define the translations.

Sincerely,
Hooman

[jimmy d]

Documentation of the gait2392 model states that the model uses Yamaguchi et al. (1989) knee model definition.

Yamaguchi G.T., Zajac F.E.: A planar model of the knee joint to characterize the knee extensor mechanism." J . Biomecl7. vol. 21. pp. 1-10. 1989.

[Hooman Shirzadi]

Hello James,

Thank you so much for your prompt response.

However, I couldn't find any equation regarding the knee coordinate translation in X and Y axis VS knee flexion angle in the mentioned paper.

I have another question. Considering the knee extension range of movement which the maximum is approximately 5 degree, could you please give me some hint about why the developers considered the range between -2.0944 and 2.0944 (-120_120) for the knee movement.

Any answers related to my question would be highly appreciated.
Thank you in advance.

Sincerely,
Hooman

[jimmy d]

From the documentation page I linked above;

Yamaguchi et al. (1989) developed a simplified model of the knee. The single-degree-of-freedom model provided by Yamaguchi et al. accounts for the kinematics of both the tibiofemoral joint and the patellafemoral joint in the sagittal plane as well as the patellar levering mechanism. Delp et al. adopted this planar knee model and specified the transformations between the femoral, tibial, and patellar reference frames as functions of the knee angle.

In Delp (1990)

The tibiofemoral contact point depends on the knee angle and was specified according to data reported by Nisell et al [21.]