Can't get contact meshes to interact

[Myles Frith-Macdonald]

I have adapted this, https://simtk.org/projects/finger, finger model by adding contact geometry.
A contact sphere at the fingertip and a contact half-plane. I have tried to add custom geometry for the fingertip but found that my mesh would appear in the GUI but wouldn't collide with the other contact geometries, so if anyone knows why that might be I'd be really grateful for any advice.
However, the built-in geometry of OpenSim works for now.

I'm also unsure of how to set up the static contact between the sphere and the halfplane. Ideally, I'd like the model to start with them in contact but I'm not sure how to do this.
Do I need to know all the offsets and dimensions and work out what the position of the finger needs to be in order for them to just be in contact?
Is there a way to set the model so that I can guarantee that the contact sphere will always be "touching" the contact halfplane?

The objective of my project is to model the forces required of the muscles to generate a specified force at the fingertip, and then use those to determine forces applied to the tendons, if I'm going about this the wrong way I'd also be grateful.

[Kyle Young]

Hello Myles,

I have been working on developing a musculoskeletal model of the patellofemoral joint. However, as I have moved deeper into the project I have run into the same problem that you had described previously, where the contact meshes of cartilage will not contact each other or their associated bone structure. With all the attempts to try to fix what was happening within the model file, it will no longer open in opensim due to the issue with the meshes and the contact themselves. I was wondering if you had any success or received any sort of information that helped you solve your problem?

Thanks,
Kyle Young