Sorry to hear that. My Samoyed/Golden Retriever mix had that happen about 6 years ago. We opted to go for the TPLO surgery for him.
Tibial-plateau-leveling osteotomy - Wikipedia, the free encyclopedia . Recovery time was about 12 weeks and in the beginning he was in quite a bit of pain but I'm happy to report that he's been 110% ever since then! If your dog is on the younger side I'd recommend having it done. It costs more but is a permanent solution, particularly if you do id active.
Oh yeah, Be prepared for it to happen to the other knee within a year. Ask me how I know !
Good luck,
Michael