Net reaction force/moment shoulder

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1

Dear experts,

I am trying to compare results I am observing for glenohumeral reactions with G. Bergmann’s results. To be sure, I am NOT running the shoulder arthroplasty/validation model so, yes, it is NOT an orange-to-orange comparison. It is simply the first attempt at shedding light on a dark area.

So, is FTotalGlobal the correct variable to compare net glenohumeral reactions reported by Bergmann’s group? If not, then which one is it? Also, is there a variable for net glenohumeral moment? If yes, where do I locate it?

I also tried the following (since I last posted the message):

In Chart 2D/3D, I go to Studies->InverseDynamicStudy->Output->BodyModel->Right->ShoulderArm->MomentMeasure->GHNetMoment-> and select F or M.

Now, the selection is confusing: Traditionally, F stands for force and M stands for moment. The values that I see for the two variables in Chart 2D/3D seem reasonable in that traditional sense. However, both F and M fall under the folder MomentMeasure/GHNetMoment/. So, are these F and M the net force and moments in the glenohumeral joint?

Thank you,

Vikas

2

Hi Vikas,

  1. It seems that you found the correct location to see the values.
    HumanModel.BodyModel.Right.ShoulderArm.Jnt.GHReactions.ResultanForce.FTotalGlobal shows the global representation of the GH reaction force.
    Main.HumanModel.BodyModel.Right.ShoulderArm.Jnt.GHReactions.ResultanForce.FTotalLocal shows the local representation of the GH reaction force with respect to the ‘gh’ node in the Scapula segment.

  2. GHNetMoment and GHNetMomentMuscles are implemented by using AnyForceMomentMeasure2 class.
    It will calculate the resultant force and moment from the listed force elements in the measure. So its output will be the global force(F) and moment(M).
    You don’t need to put too much meaning on the names of those instances of AnyForceMomentMeasure2 class.
    Also it will be better for you to see the description of the AnyForceMomentMeasure2 class.

Best regards,
Moonki

3

Hello Moonki,

Thank you for your response.

I guess I should emphasize that my goal is to compare net joint reactions and moments from AnyBody with G. Bergmann’s data and I am not sure which variable to choose.

So, which variables in AnyBody will allow me to accomplish my goal?

Is it Studies->InverseDynamicStudy->Output->BodyModel->Right->ShoulderArm->MomentMeasure->GHNetMoment-> and select F or M?

Thank you,

Vikas

4

Hello Vikas,

like Moonki said: F are the Forces and M are the Moments.

Regards,
Patrick

5

Thanks for your response, Patrick. However, I am not sure if that answers my question. Perhaps I am missing something. So, let me try to rephrase my question.

To me, AnyBody seems to provide 3 different variables for shoulder joint reaction forces:

[ul]
[li]BodyModel.Right.ShoulderArm.MomentMeasure.GHNetMoment.F[/li][li]BodyModel.Right.ShoulderArm.Jnt.GHReactions.ResultantForce.FTotalGlobal[/li][li]SelectedOutput.Right.ShoulderArm.JointReactionForce.Glenohumeral_XXX[/li][/ul]
Each of those gives me different results. Looking at the naming convention, it seems they should give me the same result!

So, my questions are:

[ol]
[li]Which one of these three variables am I supposed to choose when comparing with Bergmann’s data?[/li][li]What is the meaning of each one of these variables?[/li][/ol]
I hope this time I have made myself sufficiently clear.

Thank you,

Vikas

6

Hi Vikas,
Most of those values show exactly the same, but they show the force in a different coordinate system.
The original joint:

 HumanModel.Right.ShoulderArm.Jnt.GHReactions.ResultanForce.FTotalLocal[xxx]

shows 3 force components in a virtual reference frame. This depends on how the joint is constructed.

These vectors are transformed into a different coordinate system, similar to the ISB definition in the shoulder. You can find this in the SelectedOutput:

SelectedOutput.Right.ShoulderArm.JointReactionForce.GlenoHumeral_xxx

The developer of this model added the forces in another coordinate system, I assume that one should be similar to the Bergmann measured ones:

Main.Study.Output.GHReactionInHumerus[xxx]

I think the GHNetMoment is not a final force value, but something on the way…

If you compute the resultant force Fres = (Fx^2 + Fy^2 + Fz^2)^0.5 you will see all 3 are the same magnitude.

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