How to change varus-valgue angle?

[JAVIS (NAM)]

Hello.
I'm using Plug-in-gait_Simple model.
I did motion capture of several people. Some of them has deformity in lower limb. mostly varus. But anybody model has 0 deg angle as varus-valgus.

How to change varus-valgus angle on Plug-in-gait_Simple model?
I can only change length variable.

[depierie (Enrico De Pieri)]

Hey Javis,
I also faced a similar question not so long ago and this is what I discovered.

You can edit the varus/valgus alignment by editing: Main.HumanModel.BodyModel.Right/Left.Leg.Seg.Thigh.KneeJoint.VarusValgusRotation.

It is a fixed offset between the femur and tibia reference frame, so it might not be very realistic for very dynamic motions, but I found it to be reasonable during the stance phase of gait.

It's an editable variable (in radians) so you can change it manually by right clicking on the variable in the model tree after loading the model, assuming you know the actual value of the varus/valgus alignment for the subject you're modelling.

Similarly you could define an operation like:

Main.Studies.ParameterIdentification = {
AnyOperationSetValue SetValue_LeftValgus = {
  Target = { &Main.HumanModel.BodyModel.Left.Leg.Seg.Thigh.KneeJoint.VarusValgusRotation };      
  Source = { your measured value };
}; };

Otherwise, if you don't know the value before hand, you could still optimize it based on the markers data in this way:

  OptimizeAnthropometricsOnOff OptimizeAntropometricsOnOff (

  RIGHT_VARUS_VALGUS = ON,
  LEFT_VARUS_VALGUS = ON,
  ) ={};

This will optimize the frontal plane alignment of the knee during the model's scaling, and then maintain the identified optimal value for the rest of the kinematic/inverse dynamic analysis.
But watch out that you should ideally have both medial and lateral knee markers, at least during the static trial, and trust that they were placed accurately (i.e. watch out with patients with a lot of soft tissue).

The last approach is what I used in a recent study: https://onlinelibrary.wiley.com/doi/full/10.1002/jor.25403

[JAVIS (NAM)]

Thanks. It helps me a lot.