I'm a runner wannabe. I never really could run, and I have a bad knee as well. What helped me run, was trail running, where the ground had give and there was no pavement slamming. And very good running shoes to help cushion the knee worked wonders. And if something didn't feel right, stopping and walking a bit.
I see you're in Michigan. Depending on your knee, xc skiing might be ok during your non-biking months. Less jarring impact.