We had a partial ACL tear at 10 years, and were able to get it healed with no surgery. However, this takes a lot of vigilance and work. Our vet provided us with some information on a very slow return to activity. We actually pulled out some of the baby gates from puppyhood again, and blocked off the stairs and rooms with things he liked to jump on, like couches. We have two steps off of our deck, so we would carry out to the yard for potty time for a while. When we started walks back up, we would walk very short distances, and we very gradually built back up. During this period, it is important to remember that meds can mask the pain, and that they are very eager to please, so you shouldn't rush the process, even if they seem like they want to do more.
We tried purchasing a ramp so that he could use that to walk up to some of his favorite places. We practiced with treats up and down the ramp, and he would willing walk right up and right back down. However, no treat, and he refused to use the ramp.
We eventually just returned the ramp...
This patience was well worth it, however. In the end, we had a dog that could still walk and jump without pain, and several years later, no sign of arthritis.