Contact surface inconsistency due to partial morphing

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1

Good day @dschander @Hamed-Shayestehpour @pgalibarov

I have a question regarding the effect of partial bone morphing on the contact surface/force. I performed partial bone morphing of the distal end of the femur and distal part of the tibia. I observed that tibia bone of the generic model did not match that of the subject's tibia due to the limited number of landmarks. when registering the contact surfaces, I got the following surfaces:
image

I created an offset with the tibial bone to represent the cartilage. You can see that the blue surface is not consistent. The surface was underneath the bone at the lateral region of the blue surface (note that the surface has no holes). I do believe that this is because of the level of the morphing.

My question:
1. What would be the impact of this configuration on the contact forces calculation?

2. Does this configuration affect the penetration depth which is used to calculate the penetration volume and eventually the contact force?

The contact forces are dependent on the pressure module and penetration volume:
image

And I know that penetration volume, Vi, is approximated by
multiplying the vertex penetration depth (di) by the opponent triangle
area, Ai,
image

I do expect that di would differ depending on how well the morphing was performed (if generic bone was morphed perfectly , the offset will be more representative of the cartilage). 3. Is this true?

Best regards,
Omar

2

Omar,

we can't see how you implemented the contact. But if i were you I would not use the deformed AnyBody bone surfaces for contact - I would use real boney surfaces registered to the morphed bones. This way there will be no morphing artifacts. This is what i normally do. I am not sure how your 'cartilage' surfaces will behave for contact, but you can make a test and drive them into each other and see how they behave. You can also consider closing surfaces of your proximal tibia and distal femur.

Kind regards,
Pavel

3

I did not use the deformed AnyBody bones surfaces. The colored surfaces are those of the patient. However, since morphing was not perfect, when registering these surfaces I got something like what you see in the figure above.

4

Omar, the morphing of landmarks will be ideal. Other parts of the morphing surfaces will be interpolated/extrapolated. That means that the quality of registration will be governed by the landmarks. You can use fewer landmarks (only those that are relevant for the contact surfaces).

Kind regards,
Pavel

5

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