Hi Matthew, Welcome to the forums.
I'm assuming you weren't able to do the import by just opening the file in SolidWorks.
You should look at getting a company that provides conversion services to process the file for you. Here's a list of summaries of some vendors providing this service.
this certainly can be done in SW with the ScanTo3D add-in. the method would be to just extract the contact faces between the Femoral and Tibial parts (ST3D does a pretty good job of this) and then just reference the mesh directly (which you can do when brought in by ST3D) for the rest of the pismatic modeling of both.