Aww, Opeth, that sucks :(

Our border collie did something similar, completely destroyed his cruciate ligament. It was horrible, he was a thre-legger too.

Well, the long and short of it was that at almost eleven, we almost didn't get the operation to replace it. But we just couldn't put him down, so some hefty $$, a few pins, and teflon ligaments later, he's a happy, healthy 16 year old who JUST finished his dinner :)

Never regret that decision :) Good luck with your baby.