Hi Mark - Sorry to hear of your little one's lameness. I have some input to add to the already informative thread.
My youngest girl, Billabong, has had both back legs repaired with the procedure mentioned by Eric above. Couple criteria made this possible - her weight was ideal (under 50 lbs.) and according to the x-ray - her tibial plateau was at an acceptable slope. If you find a vet who can do this procedure they can walk you through it, of course.
The procedure my vet followed is called the Arthrex Tightrope procedure. This is the company who makes the hardware for this procedure:
Arthrex - ACL TightRopeŽ
In the old days the same procedure was used with monofiliment or fishing line leader. In fact some docs still use that today and are successful.
My vet said when one knee goes usually the other side goes as well so be wary once yours recovers unless you curb her activity you may go through the same thing on the other leg. It happened to my girl about 1 year afterwards.
Something else - I've also experienced my other girl just sprain her knee and limp for a few days to a week and then I keep her crated to reduce strain on her leg and it clears up and she's back to normal. They do a test called a "drawer test" to see if the knee joint moves in and out like a dresser drawer plus an x-ray to determine if surgery is needed.
I'll try to post some more stuff later when I have more time.
Oh yeah - the cost for the tightrope procedure like Eric said was around $1,200.