Bones movement

[Alexandra Yurova]

Hi,

there is a problem during forward dynamics simulation of knee joint motion: bones are intersecting each other, which is not physiologically correct. How one can prevent this effect? Which constraints should be used?

Regards,
Alexandra

[Thomas Uchida]

If the issue has to do with the kinematics of the model, you can adjust the definition of the knee joint. If the issue is only with the visualization, then you can adjust the size/location of the geometry attached to the Bodies. It would help to know what model you are using and how the knee joint has been defined in this model.

[Alexandra Yurova]

I use the following model: https://simtk.org/projects/kneemodel, but patellofemoral joint has more DoF.
The knee joint is defined as a custom joint.
In some experiments patella moves through tibia or femur. I am interested, which constraints should be used to prevent this.

[Thomas Uchida]

I use the following model: https://simtk.org/projects/kneemodel

Perhaps you could try contacting the authors of the model. They are likely to have experience with this issue and suggestions for how to resolve it.

[Alexandra Yurova]

It seems, that preventing of bones intersection during movement is a general problem, concerning musculoskeletal modeling in OpenSim, therefore I asked about it here.

[Thomas Uchida]

It seems, that preventing of bones intersection during movement is a general problem, concerning musculoskeletal modeling in OpenSim, therefore I asked about it here.

In general, there are a few reasons one might report "bones intersecting". Here are a few possibilities:
1. The bodies are connected to each other with a joint (e.g., pin joint at the knee) whose definition is inconsistent with the geometry that is being used to visualize the model. In this case, the joint could be redefined or the geometry could be adjusted. Note that the bone meshes do not affect the dynamics of the model.
2. The bodies are supposed to be in contact but are interpenetrating too much (e.g., contact model between the foot and floor in a forward dynamic simulation). The contact model parameters can be adjusted.
3. The intersecting bodies are not directly connected to each other (e.g., tibias on left and right legs), in which case the intersection can be prevented by limiting the model's range of motion, defining contact surfaces on the intersecting bodies, and/or adjusting the visualization geometry. Which strategy might be appropriate would depend on the simulation that is being run.

[Alexandra Yurova]

Thank you!