I partially tore my patella back in 2012. Took about two years for it to heal well enough. I still get bad tendinitis in it periodically.
But I had similar issues to wktmeow back when I first started riding. I remember one ride in which I could not pedal seated - only standing - because the pain was too much. I had to ride an hour either standing or coasting before my wife got out there to pick me up.