Knee Joint Reaction Force


I have a few questions:

  1. What is the principle of the Knee Joint Constraint Reaction Fout? There are 5 output Fout (3 forces and 2 moments) and I want to know how to calculate these?

  2. What is the original contact mechanism between thigh and shank of the default hinge knee model (AnyRevoluteJoint)?

Any help would be appreciated!

Best Regards,

Hi Lee,

  1. This is a reaction force / moment - it is calculated in the inverse dynamics step together with muscle forces by an optimization procedure we call “the muscle recruitment”. It represents an amount of force/moment a certain degree of freedom needs to “resist”/“react to” forces acting on the segments as in the Newton’s third law. The moments in the knee joint can be interpreted as the moments generated by the surface contacts wrt. to the knee joint node to counteract muscles pulling the bones.

  1. Kinematically it is a revolute joint located at the instantaneous centre of rotation. Dynamically these are compressive and shear reaction forces, plus moments to balance the out-of-the-plane torques generated by muscles and the contact surfaces as explained above.

I hope this helps. Some more information can be found in the tutorials, reference manual, and basic mechanics and biomechanics books.

Kind regards, Pavel

Hi, Pavel

Thank you for your reply, really helps! :smile:

Speaking of muscle recruitment, I want to know how to introduce the normalization factor based on the muscle volume as shown as Marra did before. Are there any tutorials?

[ Marra M A, Vanheule V, Fluit, René, et al. A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty[J]. Journal of Biomechanical Engineering, 2015, 137(2):020904. ]

Thank you very much!
Best Regards,

Yes. That is possible, even though it requires a little hack to get working. Let me see if I can find some code for it. Can you create a new topic on forum with the volume recruitment question? That way it will be easier for other users to benefit from the answer.

OK, Thank you!