Research the injury on the net before you go to the vet. Ask questions of your vet(s). Have them explain the xray to you. You need to find out to what degree the tear is. If its 1st or 2nd, try to immobilize the joint as much as possible. Maybe even a splint until the inflammation goes down. If its 3rd, you have to make a choice of surgery or let it heal on it's own. If it's a total tear...surgery. At any rate, it will be painful for a while for the dog..and you. The dog will keep his own activity limited and slowly get better. Good Luck.