Joint moments in the spine

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1

Hi,

I am interested to know the joint moments in the spine. I have tried different approaches, and had some trouble. I red a couple posts in the forum, but did not end up with a satisfactory explation.

Please correct me, if what I think is wrong or partially true in the following.
In principle, muscles are actuators in our body, and should be activated to result in zero net joint moments when the accelerations of associated joints are set to zero (assuming negligible effect because of Coriolis acceleration). So, by joint moments, I mean these moments provided by muscles only. What is the exact way of finding these moments?

To find it for L4L5 joint, I tried this code:

AnyForceMomentMeasure2 L4L5Jnt = {  
    AnyRefFrame &Ref = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.L4Seg.L4L5JntNode;
    AnySeg &Seg1     = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.L5Seg;
    AnySeg &Seg2     = Main.HumanModel.BodyModel.Trunk.Buckle.Segments.BuckleSeg;
    AnySeg &Seg3     = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.SacrumSeg;
    AnySeg &Seg4     = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.PelvisSeg;
    #include "MuscleElementList.any"  };

MuscleElementList.any includes all the muscle elements in the model whether they apply force on this joint or not. I included all the elements because it is very difficult to identify which of them are actually have effect on this joint. Will this measure exclude all the muscle force elements that do not apply to L4, and give what I intented to obtain? Or, I need to do something else?

Kind regards,
Riza Bayoglu.

Biomechanical Engineering Department
University of Twente.

1 Like
2

Hi Riza,

That is supposed to be the right approach. You might be missing contribution of the muscles attached higher than these levels. Do you have a particular problem with this approach?

Kind regards,
Pavel

P.S. Sorry for answering late - have been very busy.

3

Hi Pavel,

Thank you for your message. Please see attached picture of the current trunk model that I am working on.

Starting from Sacrum joint, I issued similar commands to extract the moments in the MuscleMoment.txt file. MuscleElementList.any includes all the muscle elements in this model. Note that I do not have shoulder and arm body parts, so their muscles excluded. A flexion analysis of 36 degrees (motion performed by a combination of pelvis, lumbar and thoracic spines) yielded the results shown in the JointMoments.xlxs file.

I failed to understand what they actually mean. As I said before, I only need to extract moments provided by muscles. I understood from the reference manual that below code performs a free body analysis at the L4L5JntNode. So, it only includes segments below L4, and all the muscles that attaches to these segments, and gives and equivalent force and moment at the specified joint. To my understanding, this equivalent moment is the moment provided by the muscles. But, the results I produced did not make sense to me. Probably I misunderstood something.

  AnyForceMomentMeasure2 L4L5Jnt = {  
    AnyRefFrame &Ref = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.L4Seg.L4L5JntNode;
    AnySeg &Seg1     = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.L5Seg;
    AnySeg &Seg2     = Main.HumanModel.BodyModel.Trunk.Buckle.Segments.BuckleSeg;
    AnySeg &Seg3     = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.SacrumSeg;
    AnySeg &Seg4     = Main.HumanModel.BodyModel.Trunk.Segments.SegmentsLumbar.PelvisSeg;
    #include "MuscleElementList.any" };

Do you have any idea about this?

Regards,
Riza.

4

When you say do not make sense - what exactly do you think is wrong?

Pavel

5

I estimated the moment at T12L1 joint from head, neck and thorax massess for standing and flexed positions. They were around -0.3 and -35 Nm, respectively. However, the model gave -0.6 and -21.6 Nm instead.

6

Riza,

Yes, it probably sounds a bit too high, but 2.5kg over 1 m in a flexed position - might not be too unrealistic. I guess the thorax length is 45 cm + neck + head, depends on how much flexion you prescribed i guess.

Secondly, I am not sure what is exactly included in the muscle list - could it be that something is missing? I can also see that it is not our model from the repository - so I just assume that the thoracic part is completely rigid and nothing was changed for the rest of the configuration.

I think it is a bit hard to say what we are supposed to see - what I would do is go from the simpler configuration towards a more complex one. I would isolate a single muscle and see what happens for this one, how much torque it generates. I am afraid with the current question we will simply speculate about what we are supposed to see. Could you come up with another question that might help you to answer this question?

Kind regards,
Pavel