I started a discussion to demonstrate how to converge STL files into Geometry that you might find helpful.
I plan to make more videos to show the cartilage, meniscus and ligaments.
You can take your STL file and reprocess it to geometry then mesh with more elements through the thickness. Linear elements are more robust than quadratic elements for contact models.
I have seen models with linear elastic material properties that stopped convergence at some point and after the material was changed to hyperelastic, converged to the end.
You can make the bones rigid and use a rotational joint to rotate it about any axis you want. The joint is created with its own local Csys and you can put the origin anywhere and orient the Z rotation axis in any direction you want. The joint can be to ground or between two bodies.