Agree that surgery is the best option. A cruciate tear in dogs is very different than in humans.
Severe arthritis is a result of not repairing a torn cruciate in dogs and that starts almost immediately...not years. Here is a link to an article my ortho surgeon wrote:
http://yorkiehavenrescue.com/cruciateligament.html
I have had quite a few yorkies who had this surgery and they did very well. My own personal pup, Cookie, had it and she is a very active girl.
Good luck with your baby and please let us know what you decide...