I was in the same situation a few years ago with my then 7 yr old female American lab duck retrieving machine. I consulted with a few vets, and one old timer suggested Long term rest and the scar tissue would stabilize the knee. From October to April that dog laid in her bed and only got up,to do her business. The scar tissue did stabilize and she was able to run in a straight line. I never had her off leash until she passed 6 yrs later.