Modelling bones

Hi, I'm trying to make a mechanical model of the finger using 3D scans of the individual bones. Is there a way to lock the placement of a part to a plane or more helpfully a curved surface that is not physically part of the model, like creating a un-interacting surface and locking to that. I'm completely new to Creo, and CAD in general, so any help or suggestions that might be helpful would be appreciated, not just this specific question.

Thanks very much

Ben