Facet joint and ligaments in lumbar spine

Hi,

I am trying the AMMRV1.3.1 and focus on the lumbar spine model. I find that in the standing model, there are ligaments and disc stiffness for lumbar region, but no facet joint. And there is a facet joint model separately.

1 I don’t which one is the standard model for lumbar spine.
2 If I want to combine these two model to get a model with facet joint, ligaments and disc stiffness, could I just combine them without changing stiffness/force of facet joint, ligaments and disc?

Thanks,
Best regards,
Rui

Hi Rui,

  1. There is no ‘standard’ model of the lumbar spine with facet joints - you can find two implementations of the facet joints in the repository in Applications/Examples folder, however, they are only demonstrations of the mechanisms that can be employed to model them:
    SpineFixationWithForceDepKinematics and FacetJointModel.

The latter one is described in: “Implementation of facet joints in a detailed musculoskeletal lumbar spine model based on inverse dynamics”, Mark De Zee. And the former one is an experimental mechanism. No validation has been done on any implementation and as such it is not yet included in the standard body model.

  1. Please have a look at the “SpineFixationWithForceDepKinematics” example. It combines all these components and uses a Force-dependent kinematics approach, which means that the kinematics will be computed taking into account facet joint contact forces. However, please, bear in mind that this facet joint implementation is experimental. Try to investigate how it works and what modifications are needed for your model.

Best regards,
Pavel

Thank you very much. It helps!

Hi Pavel,

I try the “SpineFixationWithForceDepKinematics” example. It is a nice model, but the forces in the facet joints are always 0 when flexion, extension and so on. Did I make a mistake or it is 0. You said the facet joint implementation is experimental, and is that means I should modify the facet joint by myself if I want to use it?

The Force-dependent kinematics approach is a new approach and it is not used in the ‘StandingModel’. Are there some validation studies for this approach?

Thanks
Best regards,
Rui

Hi Rui,

The contact forces do appear in the model (we have recently checked that) - please try to expose the model to a larger range of motion as the surfaces might not simply reach each other.
And secondly please check if the facet component is switched on in the example.

And regarding the validation on force-dependent kinematics + spine - we are working on that right now. In the AMMRv1.3.1 it is still a demonstration of the FDK facility.

Best regards,
Pavel

Hi Pavel,

Thanks a lot. Yes, there are facet forces when I exposed the model to a larger range of motion.

Another problem is that I try to include the arms and legs (only bone without muscles) in the “SpineFixationWithForceDepKinematics” to get a full body model, but it showed “Model is kinematically indeterminate : Position analysis failed : 367 independent constraints and 399 unknowns” when calculation. Should some parameters be turned on or this model is an example just for spine region?

Best regards,
Rui

Hi Rui,

You need to define some motion/constraints for the newly added components.

Regards,
Pavel

Dear Pavel,
I’ve read your statements. There was mentioned that ligaments and disc stiffness are included in the lumbar model! But due to ‘A generic detailed model …’ by Mark de Zee et al. , ligaments are excluded in the lumbar model. However, they’ve not discussed about disc stiffness.
I found the discs as simple spherical joints with no sign of stiffness.

Please let me know if ligaments and esp. disc stiffness are contributed in your model. (I’m using AMMR v1.0 , AMS v4.0)

Thanks in advance,
Mohamad

Dear Mohamad,

These ligaments were introduced later. You are using quite an old version of AMS and AMMR. I think you could either define these structures yourself or get newer version of AMS/repository.

Regards,
Pavel

Thank you Pavel,
And how about the disc stiffness? Is it included in the model I’m using?

It is included as a cumulative stiffness of the whole joint + surrounding ligaments. Individual components were introduced later at the same time.

Regards,
Pavel

Thank you again Pavel,
And finally, in which sub-file I can find that stiffness? I almost searched whole the code.

Hi Mohamad,

I was wrong about your version of the repository - there is no cumulative stiffness in that one either. It will have to be implemented.

Regards,
Pavel