I'm glad you had the knee checked out. We depend on them for so much more than even cycling so it's not something to mess with. I had a problem with my knee in early '88 that indirectly led to my accident that put me on disability and a downward spiral until I recently started riding the bike again. We never found out what was the problem with mine, other than I'm prearthritic and have since had some slight meniscus tears (likely due to all my weight wear and tear) I know I have to listen to my knees if I want to keep on the road (literally) to better health and hopefully complete recovery from all my physical problems.
Follow what the doc says and good luck, thanks for keeping us updated.
Mary