knee lateral moment

Main Forum
1

Dear somebody in AnyBody,

I just run inverse dynamics analysis using GiatLowerExtremity model (AMMRV1.31, AnyBody version 5) using C3D data. When I checked on the Selected Ouput, we have : Knee lateral moment.

My questions are:

  1. What is the meaning of knee lateral moment? is it knee varus-valgus moment? if yes, can anybody tell me when it is positive, which direction of this moment pointing out to? and vice versa when its negative.

When I check the model, this direction was relative to the thigh coordinate system.

Thanks for the help
Kindest Regards
A.D. Wibawa

2

Dear A.D. Wibawa,

Yes, your guess is right. The knee lateral moment is as same as the varus-valgus moment.

If you see ‘…\AMMR\Body\AAUHuman\LegTD\LegMoments.any’ file, then you can see the following code.

AnyForceMomentMeasure KneeJointReactionMoments = 
{
  AnyForceBase &Force = ..Jnt.Knee.Constraints.Reaction;
  [b]AnyRefFrame &Thighknee = ..Seg.Thigh.KneeJoint[/b];
  AnyVec3 Mlocal = M*Thighknee.Axes;
};

And Knee_LateralMoment value came from the first component of Mlocal value of above measure,
the sign of Knee_LateralMoment follows the coordinate system of Thigh.KneeJoint reference nodes.

Attached please find a snapshot of the KneeJoint coordinate system.
Then according to the right-hand-rule around the X-axis, you can find which direction will have the positive sign.

Best regards,
Moonki

3

Dear moonki,

Thanks for sharing about knee lateral moment, since in the model, the knee joint is a point contact between femur and tibia, so knee varus-valgus direction is in vertical direction (y axis), is it correct?

And since this is a moment, moment is (force x moment arm)some distance which is perpendicular to the center of rotation. Can we know from the model how much is that distance defined in the model?

Correct me please if I understand wrongly.

Thanks again
Kind Regards
A. D Wibawa

4

Adhi,

The knee is a revolute joint around the v-v axis = z-axis (not y-axis). as you can see in Moonkis picture.

The moment is calculated by

  1. Force: all muscle forces applied in the muscle attachment points and
  2. Moment arm: the distance of the muscle att. points to the joint center
5

Thanks Amir for your explanation,

Please clarify me if I am wrong.
I still don’t understand with the moment direction. So, when it is positive, the moment is directing to the z axis and when it is negative the moment is pointing out to minus z axis. if this is the case then its the same as knee medial and lateral side? (correctme if I am wrong)

I guessed that the varus-valgus moment is pointing out at y-azis (positive or negative respectively) but the question is then, at which side? lateral or medial?
(I thought like this based on its name: knee lateral moment)

I need your explanation on this point.

Kindest Regards
A. D Wibawa

6

Adhi,

If you are unsure about moments in a joint, the only way to understand them is to make a simple example.

Take the FreePosture model, position the hip joint straight and include following force applied to the foot:

AnyForce3D FootForce = 
{
  F = {0,0,100};
  AnyRefNode &ToeNode = Main.HumanModel.BodyModel.Right.Leg.Seg.Foot.GroundJoint;//
 };
 AnyDrawVector DrawForce = {
   Vec = .FootForce.F*0.0025 ;
   GlobalCoord = Off;
   AnyRefNode &SphereI = Main.HumanModel.BodyModel.Right.Leg.Seg.Foot.GroundJoint;//Right; 
   Line.Thickness=0.0025;
   Line.RGB={0,1,1};
   Line.End.Style = {5} ;
   Line.End.Thickness = 3*Line.Thickness;  
   Line.End.Length = 4*Line.Thickness;
   Line.Start.Style = {0};
   Line.Start.Thickness = 3*Line.Thickness;  
   Line.Start.Length = 3*Line.Thickness;
   Line.Start.RGB = {1,0,0};
 };

If you apply 100N and then switch to -100N you can see the moment changing and you’ll see what direction it is applied.

7

Dear Ali and Moonki,

I understand now the axis and the direction of knee varus valgus moment, thanks for the example code. However, further question will be, can knee lateral moment from Anybody say which moment is that, whether it is a knee varus moment or knee valgus moment? or maybe AnyBody takes an assumption that all knee lateral output is knee varus moment??

Thanks for sharing
Kindest Regards
Adhi

8

Adhi,

first, my name is not Ali, second, your new question assumes that you did not understand the axis and the direction of the varus valgus moment.

have look at that simple sketch:

http://annals.org/DownloadImage.aspx?image=/data/Journals/AIM/19967/16FF3.jpeg&sec=23917520&ar=713937&imagename=

the difference between varus moment and valgus moment is only the direction. From the example, one force will lead to the varus moment, when switching the sign, it will lead to the valgus moment. AMS shows that in plus or minus moment.