Validity of Inverse dynamics for orthosis users

[Ganesh B]

Hi all,
Is it valid to perform inverse dynamics on subjects wearing a Knee-Ankle-Foot Orthosis (KAFO), specifically for the braced limb?
Any literature or insights? I have come across literature related to inverse dynamics of above knee amputation (prosthesis) but not much related to inverse dynamics of braced leg?
Thanks in advance for your suggestions and answers.

[Chris Kirtley]

Re: Validity of Inverse dynamics for orthosis users

Great question, Ganesh. Most inverse dynamics models assume the joints are frictionless pin-joints (in 2D) or universal joints (in 3D}. Of course an orthosis acts on the limb with 3-point or 4-point control, so strictly speaking the forces at these points would need to be modelled. That's easier said than done, because you probably don't know the magnitude and precise point of application of these forces. Can you forget about that and just model the whole system as a moment? I must admit I don't know!

[Ross Miller]

Re: Validity of Inverse dynamics for orthosis users

Ganesh,

I'm not very familiar with those devices, but would it be possible to determine a torque-angle relationship(s) for it in isolation? You could then do regular inverse dynamics and calculate/estimate the fraction of the moments that are from the orthosis vs. biological.

Scott Brandon did a similar thing here (chapter 4):

https://qspace.library.queensu.ca/handle/1974/12707

Ross

[Ganesh B]

Re: Validity of Inverse dynamics for orthosis users

Thank you Chris for your insights!
Yes, Orthosis with the limb forms an indeterminate system. So,assuming limb with the orthosis as a single rigid body and no relative motions, is one way to solve the equations as some literature suggests.
I will look into your suggestion. But, I didn't get exactly what do you mean by.."just model the whole system as a moment"

[Ganesh B]

Re: Validity of Inverse dynamics for orthosis users

Thanks Ross. I will check the literature suggested.