I was told to work the muscles around the knee. Most of my work is short arc stuff because any deep squats or anything that strains the knee when it is bent around 90 degrees inflames my knee. If you want I can show you a stretch that you are going to hate that keeps my knee flexible. I am sure there is some very creative strength stuff out there at this point. Its been years since I tore my ACL but I can show you what I do to keep my knee going but the biggest thing for me was to get my bike setup properly and then to get my ass out on it.
"Yesterday I was clever and tried to change the world. Today I am wise and try to change myself." -Rumi