I recently had a discussion with the surgeon I use. I have had a few orthopedic cases just this past year with my fosters. This surgeon is board certified and amazing! He is not quick to operate on dogs.
His opinion is that a torn cruciate ligament on a yorkie (actually any dog) must be surgically repaired. He said that if you let it go, it will cause many problems later...and most definitely will quickly develop into severe arthritis.
This was not in response to my having a pup with a torn ligament at this time. This was just a general discussion on a follow up visit for another pup. So, there really was nothing to be gained by his telling me that.
What I will say is that I would never allow any vet but a board certified one to do orthopedic surgery on any or my pups...personal or fosters.
You can find board certified surgeons at:
American College of Veterinary Surgeons