I got my recumbent stationary bike after my first knee replacement. I couldn't walk or ride an upright because of the weight on the knee, but the recumbent gave me full range of motion and strengthening of both muscles and tendons. I started out with 5 slow minutes and worked my way up. It is now my go-to default cardio and I put in an hour most days which equals 11 to 12 miles. I keep things interesting by getting a full season DVD set of interesting TV shows from the library and popping one episode in each evening. Most shows have about 22 episodes, so after my three weeks I've gone over 250 miles and it's time for a new show or a new season.
Shoot for the moon. Even if you miss you will land amongst the stars.
Nothing changes when nothing changes.