Influence of Disc Stiffness and Ligaments

Hi all,

I am investigating the influence of head mass, disc stiffness and presence of ligaments on the loading of the cervical joints.

I have ran a couple of simulations by changing the disc stiffness from no to linear to nonlinear as well as switching on and off the ligaments in the cervical spine. I found there is no different in terms of joint reaction forces in any of cervical levels whether disc and ligament switched on or off for the same subject.

Is there any reasons for this or have I ran these simulation wrong?

Do I need to run a different parameter identification for individual change of parameter (one anyset for no disc stiffness, one anyset for linear stiffness, etc etc)?

I'd really appreciate if someone could shine a light how should I go about with this.

Thank you.

Kind regards,
Faizal

Hi Faizal,

Do you run default AMMR model or with your own modifications? I believe we talked about modelling cervical spine as FDK, and this needed ligaments, which are not implemented in the default AMMR. I'd expect to see no difference if you don't have the objects.

Kind regards,
Pavel

Hi Pavel,

Apologies for not giving some background details on this.

This investigation is just a quick study to see the influence of head mass, disc stiffness, and ligaments in the model.

I used full body model from AMMR without any modifications. FDK was not switched on in this study and kinematic rhythm was used. And I used C3D mocap data from subjects doing acitivities involving the neck as the driver for the model. Majority ofsoft drivers were switched on.

Parameters for disc stiffness (none, linear, non-linear) and ligaments (on/off) were tweaked from BodyModelConfig.any

Head mass was tweaked from Main.HumanModel.BodyModel.Trunk.ModelParameters.HeadWithoutNeckMass

Changing the head mass does influence the cervical joint reaction forces. However, disc stiffness and presence of ligaments has a very miniscule effect (0.001 N) for the same subject and same mocap driver.

Let me know what do you think.

Thank you.

Kind regards,
Faizal