Inputs for Adding Muscles and Ligaments into Foot/Ankle Model

[Michael Asmussen]

Hi Everyone,

I am looking at inserting a number of ligaments of the ankle and foot into the current "Gait2392_Simbody" model.

I was wondering if anyone knows of any references to estimate the max force these ligaments can produce, their force-length curve, resting length, and origin/insertion? If not, is there a method that can be used to provide an approximation of the max force and force-length curve of these ligaments?

Similarly, is anyone aware of any references to provide the the necessary parameters to model the intrinsic muscles of the foot? If not, a method to provide an approximation for these parameters?

Thank you!

Mike

[Michael Asmussen]

Hi Everyone,

I have resolved the intrinsic foot muscle questions, but if anyone has insight into the questions about the ligaments (pasted again below), that would be great

Thanks!

Mike

I was wondering if anyone knows of any references to estimate the max force these ligaments can produce, their force-length curve, resting length, and origin/insertion? If not, is there a method that can be used to provide an approximation of the max force and force-length curve of these ligaments?

[Christopher Dembia]

Matt Demers modeled passive tissues at the ankle joint (so, not instrinsic ligaments) using a "bushing force." For example, OpenSim has a "ExpressionBasedBushingForce" component. This would be an alternative to using path-based ligaments. The "ExpressionBasedBushingForce" allows you to define the force-length curves of the force element somewhat freely. Since there is no path, then there would be no need to specify origin/insertion points. See Fig 2 in http://nmbl.stanford.edu/wp-content/upl ... rs2017.pdf

Maybe you already found it, but this paper (http://www.sciencedirect.com/science/ar ... 01478#fig2) has some details about foot modeling and contains a table with the yield strength and strain of ligaments in the foot. I'm not sure how useful that is. Also, the paper has a supplementary PDF that might provide some useful information about other foot models.

Other members of the OpenSim might know more about existing foot models/data.

This is unrelated to your question, but I was just wondering: What DOFs do you have within the foot, other than the MTP joint? That is, what would the ligaments crossing the arch do? Are your current DOFs sufficient?

[Michael Asmussen]

Hi Chris,

Thanks for the insight! I think the approach by Matt Demers might be a good alternative to the path-based ligaments if I cannot find suitable literature to support how to put the ligaments in the model.

No, I have not found this article yet and thanks for passing it along! I have currently been focusing on the intrinsic foot muscles, but this will "jump start" my ligament modelling.

In the standard Gait_2392 model only has the MTP joint along with a PF/DF joint and an In/Ev joint. The KU Leuven has a few more DoF. I might adapt their model when including the ligaments and muscles of the foot. Can you add DoF to the model via the GUI or is this addition solely down in the xml file?

Thanks Chris!

Mike

[Sanne Vancleef]

Hi Michael,
A colleague of mine is also working on the implementation of ankle ligaments (Tiago Malaquias). He is not participating in this workshop, but it might be interesting to get in touch with him. This is the link to his paper: http://www.tandfonline.com/doi/abs/10.1 ... 16.1206533.

Kind regards,
Sanne

[Michael Asmussen]

Hi Sanne,

Thanks for the input!

I believe I have downloaded your colleagues model (KU Leuven Foot Model) and am thinking about adapting it to a model I would use.

I will definitely contact him about implementing the ligaments.

All the best and thanks for the suggestion!

Mike