Precisions on the shoulder

Hi !

I will try to ask precise questions…

For the glenohumeral joint, you said it was possible to define it like
a contact between two ellipsoids. Can you tell by which way ?
Will this model be able to provide slide of a bone on the other?
Can we see friction forces?

If it’s complicated, is it possible to know displacement forces, i
mean, not only the pressure onto the glenoid ?
You wrote if we disable a muscle, we could have the loads
redistributed on other muscles but could we see the forces in the
joint in all directions ?

I explain : in case of a massive tear of the rotator cuff, the GH
joint is not a ball-in-a-socket joint any more but could provide
rotation AND gliding movements… I’m interested in the both. The aim
of the model is not to dislocate.

Thanks a lot

Yoann

Hi Yoann

It is possible to define it like a contact between two ellipsoids.
It is done by creating a mechanism using the normal elements of
AnyScript, this mechanism will act like two ellipoids in contact. It
ends up being a very complicated mechanism to control, so i would
not recommend this, but if you are still interested we have a
preliminary knee model that uses this technique. This model will not
take into account dynamic friction. But sliding should be possible,
if you drive the sliding motion.

You can see all the reactions in the GH today by looking in this
location of the output tree

Main.Study.Model.HumanModel.Right.ShoulderArm.Jnt.GHLinCon.Reaction.F
out

It gives a vector with three elements containing the GH reaction
forces.

Another option could be to switch off the side way reactions in the
GH joint. If you do so the muscles will have to carry the sideways
forces. The joint will not dislocate but it will not be able to take
up sideways forces. If you want to do this it should be changed in
the BRep/aalborg/Arm3d/Jnt.any, by a redefinition of the GH joint,
where the reactions in the GHLinCon should be changed. This is
ofcourse a drastic change to the model and i am not sure if this is
what you would like to do, this will remove all sideways forces in
the GH joint.

Please do not hesitate to ask again if you have further questions

Best regards
Soeren AnyBody Support

I think the e
— In anyscript@yahoogroups.com, “Yo” <yoann.collet.1@e…> wrote:
>
> Hi !
>
> I will try to ask precise questions…
>
> For the glenohumeral joint, you said it was possible to define it
like
> a contact between two ellipsoids. Can you tell by which way ?
> Will this model be able to provide slide of a bone on the other?
> Can we see friction forces?
>
> If it’s complicated, is it possible to know displacement forces, i
> mean, not only the pressure onto the glenoid ?
> You wrote if we disable a muscle, we could have the loads
> redistributed on other muscles but could we see the forces in the
> joint in all directions ?
>
> I explain : in case of a massive tear of the rotator cuff, the GH
> joint is not a ball-in-a-socket joint any more but could provide
> rotation AND gliding movements… I’m interested in the both. The
aim
> of the model is not to dislocate.
>
> Thanks a lot
>
> Yoann
>

Hi Soeren and thank you for the precisions,

Still some little things :

> But sliding should be possible,
> if you drive the sliding motion.

Ok, but the aim is to see if there is sliding, when only driving an
abduction. It’s not possible if i well understood, is it?
I mean, if you don’t drive a slide of the humeral head on the glenoid,
the centres of rotation will stay the same for the both. Am i right?

> Another option could be to switch off the side way reactions in the
> GH joint. If you do so the muscles will have to carry the sideways
> forces. The joint will not dislocate but it will not be able to take
> up sideways forces.

If we can’t see a passive displacement of the humeral head, the
sideways reactions would give directions where the head would go if
the model was able to let it. So we won’t switch off sideways
reactions and maybe will keep this solution in mind.

Thank you

Yoann

Hi Yoann

You are right about the sliding, the model will not predict any
slide, the motion is driven.

It is also right that the sideways reactions will tell
which direction the slide would occur if possible.

Best regards
Soeren AnyBody Support

— In anyscript@yahoogroups.com, “Yo” <yoann.collet.1@e…> wrote:
>
> Hi Soeren and thank you for the precisions,
>
> Still some little things :
>
> > But sliding should be possible,
> > if you drive the sliding motion.
>
> Ok, but the aim is to see if there is sliding, when only driving an
> abduction. It’s not possible if i well understood, is it?
> I mean, if you don’t drive a slide of the humeral head on the
glenoid,
> the centres of rotation will stay the same for the both. Am i
right?
>
> > Another option could be to switch off the side way reactions in
the
> > GH joint. If you do so the muscles will have to carry the
sideways
> > forces. The joint will not dislocate but it will not be able to
take
> > up sideways forces.
>
> If we can’t see a passive displacement of the humeral head, the
> sideways reactions would give directions where the head would go if
> the model was able to let it. So we won’t switch off sideways
> reactions and maybe will keep this solution in mind.
>
> Thank you
>
> Yoann
>

Hi Yoann,

This is John. I think you can predict whether the joint will be
stable or not with AnyBody, but you cannot predict how much it will
move if it becomes unstable.

If the joint loses stability, it will show in the inverse dynamics
analysis as either very high muscle activation or an inability to
solve the equilibrium equations.

It will require a modification of the existing repository GH joint
to account for the unilateral contact forces in the joint. The
current repository model has a ball-and-socket joint wich can carry
tension as well as compression. You need to refine this joint to
only handle compression and only within the hull of the joint socket.

Best regards,
John

— In anyscript@yahoogroups.com, “AnyBody Support” <support@a…>
wrote:
>
> Hi Yoann
>
> You are right about the sliding, the model will not predict any
> slide, the motion is driven.
>
> It is also right that the sideways reactions will tell
> which direction the slide would occur if possible.
>
> Best regards
> Soeren AnyBody Support
>
>
> — In anyscript@yahoogroups.com, “Yo” <yoann.collet.1@e…> wrote:
> >
> > Hi Soeren and thank you for the precisions,
> >
> > Still some little things :
> >
> > > But sliding should be possible,
> > > if you drive the sliding motion.
> >
> > Ok, but the aim is to see if there is sliding, when only driving
an
> > abduction. It’s not possible if i well understood, is it?
> > I mean, if you don’t drive a slide of the humeral head on the
> glenoid,
> > the centres of rotation will stay the same for the both. Am i
> right?
> >
> > > Another option could be to switch off the side way reactions
in
> the
> > > GH joint. If you do so the muscles will have to carry the
> sideways
> > > forces. The joint will not dislocate but it will not be able
to
> take
> > > up sideways forces.
> >
> > If we can’t see a passive displacement of the humeral head, the
> > sideways reactions would give directions where the head would go
if
> > the model was able to let it. So we won’t switch off sideways
> > reactions and maybe will keep this solution in mind.
> >
> > Thank you
> >
> > Yoann
> >
>

Hi Soeren,

In order to simplify, you have to know i am working on a reverse
prosthesis (delta) of the soulder.
What i wanna do is to see if we are able to mesure the impact of the
size of glenoid or humeral part.
I want to test the effect of several diameters on the kinematics and
force in the muscles.

So if you don’t have a real surface that could not work.
You said to me the .stl files are only visual cause muscles are
supported by the bonny surface defined before but how can we do to
change it?

What are the fondamental elements of Anybody, ie the virtual
mechanical elements making the bones “acting” like surface? I know
they are not FE but i didn’t understand their nature. What are the
contact between two bones, can we modify those contacts?
Maybe we will find a way to make something better.

Tank you very much for your patience

Yoann

— In anyscript@yahoogroups.com, “AnyBody Support” <support@a…> wrote:
>
> Hi Yoann
>
> You are right about the sliding, the model will not predict any
> slide, the motion is driven.
>
> It is also right that the sideways reactions will tell
> which direction the slide would occur if possible.
>
> Best regards
> Soeren AnyBody Support
>
>
> — In anyscript@yahoogroups.com, “Yo” <yoann.collet.1@e…> wrote:
> >
> > Hi Soeren and thank you for the precisions,
> >
> > Still some little things :
> >
> > > But sliding should be possible,
> > > if you drive the sliding motion.
> >
> > Ok, but the aim is to see if there is sliding, when only driving an
> > abduction. It’s not possible if i well understood, is it?
> > I mean, if you don’t drive a slide of the humeral head on the
> glenoid,
> > the centres of rotation will stay the same for the both. Am i
> right?
> >
> > > Another option could be to switch off the side way reactions in
> the
> > > GH joint. If you do so the muscles will have to carry the
> sideways
> > > forces. The joint will not dislocate but it will not be able to
> take
> > > up sideways forces.
> >
> > If we can’t see a passive displacement of the humeral head, the
> > sideways reactions would give directions where the head would go if
> > the model was able to let it. So we won’t switch off sideways
> > reactions and maybe will keep this solution in mind.
> >
> > Thank you
> >
> > Yoann
> >
>

Hi Yoann

Ok thanks, this gives a better view of what you want to do.

I will try to explain how the .stl files works. The stl files works
only as a visual representation of the bones surfaces. In order to
make muscles wrap around them, various geometrical primitives such
as spheres, cylinders etc. have been fitted to match their surface
in the regions where the muscle wrapping occurs. When you scale the
model the bones and the geometrical primitives will scale together.

The .stl files do not have any effect on the kinematics, the
kinematics is controlled by the various joints which can be defined
in AnyBody and non of these involes the bone surfaces.

So it is not possible in AnyBody to create a joint which takes
contact between two bony surfaces defined as .stl files into
account.

I have an idea on how to make a joint between two spheres of
different radius, but i am not sure if it will be of any use for
this purpose. If the difference between the glenohumeral raidus and
the humerus radius is small it will not have any effect, then the
kinematics will resemble the spherical joint. The joint can be
contructed as a mechanism using the standard elements in AnyBody. It
will constrain only one dof, so the two dof sliding between the
spheres will have to be driven manually. In other words this means
that the model will not by itself find the the correct contact point
between the two spheres this will have to be driven, in reality the
shoulder would find this contact point giving the equilibrium by
itself.

The correct contact point between the two spheres will be the point
where the contact force is radial to the two spheres, without need
of any tangential forces. In practise this will only work for static
situations since you will have to make a parameter study to
determine the correct location of the contact point between the two
spheres that will remove the need of any tangential force.

Here is a short description on the mechanism i have in mind:

1 a segment is attached to the scapula by a spherical joint in a
point close the gh joint we use today. It has the length equal to
the size of the radius of the scapula part (glenosphere)
2 a segment is attached to the humerus using a spherical in a
location lying close to the GH center we use now. This segment has a
length equal to the humerus cap size.
3 kinematic constraints between the two new segments is setup at
their end points. These kinematic constraints must ensure that long
axes of the new segments is alligned, meaning that their normals are
identical, and that the end points are in contact.
4 artificial strong contact muscles between the end points need to
be defined that will allow only for compression forces, sideways
reactions needs also to be allowed
5 by moving the humerus sligthly the contact point between the two
spheres will move around and the location where there is no
tangential force needed between the two new segments is the correct
contact point.

It will require a fair amount of work to implement this and make it
work as intended, but in principle i think it is possible. If you
decide to do so i would strongly recommend to build the joint from
scratch initially in a seperate model and play around with it to
make sure it works as intended before replacing the GH joint with it.

Best regards
Søren AnyBody support

— In anyscript@yahoogroups.com, “Yo” <yoann.collet.1@e…> wrote:
>
> Hi Soeren,
>
> In order to simplify, you have to know i am working on a reverse
> prosthesis (delta) of the soulder.
> What i wanna do is to see if we are able to mesure the impact of
the
> size of glenoid or humeral part.
> I want to test the effect of several diameters on the kinematics
and
> force in the muscles.
>
> So if you don’t have a real surface that could not work.
> You said to me the .stl files are only visual cause muscles are
> supported by the bonny surface defined before but how can we do to
> change it?
>
> What are the fondamental elements of Anybody, ie the virtual
> mechanical elements making the bones “acting” like surface? I know
> they are not FE but i didn’t understand their nature. What are the
> contact between two bones, can we modify those contacts?
> Maybe we will find a way to make something better.
>
> Tank you very much for your patience
>
> Yoann
>
>
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@a…>
wrote:
> >
> > Hi Yoann
> >
> > You are right about the sliding, the model will not predict any
> > slide, the motion is driven.
> >
> > It is also right that the sideways reactions will tell
> > which direction the slide would occur if possible.
> >
> > Best regards
> > Soeren AnyBody Support
> >
> >
> > — In anyscript@yahoogroups.com, “Yo” <yoann.collet.1@e…>
wrote:
> > >
> > > Hi Soeren and thank you for the precisions,
> > >
> > > Still some little things :
> > >
> > > > But sliding should be possible,
> > > > if you drive the sliding motion.
> > >
> > > Ok, but the aim is to see if there is sliding, when only
driving an
> > > abduction. It’s not possible if i well understood, is it?
> > > I mean, if you don’t drive a slide of the humeral head on the
> > glenoid,
> > > the centres of rotation will stay the same for the both. Am i
> > right?
> > >
> > > > Another option could be to switch off the side way reactions
in
> > the
> > > > GH joint. If you do so the muscles will have to carry the
> > sideways
> > > > forces. The joint will not dislocate but it will not be able
to
> > take
> > > > up sideways forces.
> > >
> > > If we can’t see a passive displacement of the humeral head, the
> > > sideways reactions would give directions where the head would
go if
> > > the model was able to let it. So we won’t switch off sideways
> > > reactions and maybe will keep this solution in mind.
> > >
> > > Thank you
> > >
> > > Yoann
> > >
> >
>