A torn meniscus is to cycling as the gates of St. Peter are to heaven. Or a pit of quicksand is to a women in a '60s film. What I'm trying to say is that more people have gotten into the sport because of cartilage trouble in their knees than have gotten into yo momma after she's been drinking (just a figure of speech). If it's not the best exercise to stabilize and strengthen the joint, it's close. I'm sure as you ride more and continue to build strength, your knee will come around to standing on the pedals, and it sounds like it already has. Standing on the pedals is still a very controlled motion, and even if you're pedaling a relatively tall gear, the forces aren't severe -- it's closer to like climbing a set of stairs than it is to anything you'd do on a basketball or tennis court. Just listen to your body, take it a bit at a time, do what works, and be patient with yourself. I got into cycling because of a arthroscopic surgery at age 14, knees feel great all these many years later.