My husband has had three knee surgeries and has increased his riding after every one of them (mostly because every other activity has gradually been deleted from the list of things he can do ... swimming being the most recent; who knew it was so hard on knees). The only things he did were to switch from the road bike to the mountain bike for a while, because it's a little more stable and he found that the muscle loss from surgery meant that he needed to take it slowly, and after something like an ACL reconstruction you really, really need to avoid falls.

His third surgery was for a broken tibial plateau after the top of his tibia broke off completely, right at the spot where he'd had a pin inserted for his ACL replacement three years earlier. That was after a rock-climbing fall, but it wasn't much of a fall and I think it made him much more aware of how fragile that leg is. He still rides a lot but he is not the crazy mountain biker he once was. His riding is almost exclusively on one of the road bikes now; he has barely touched his mountain bike since he finished his last rehab. (He found that it was better for rehab riding, but he was sticking to flat trails.)

A friend of mine has also just had her second ACL surgery and a lecture from the doctor about how she really does have to stop running. My dad had four knee surgeries before he finally had to have a knee replacement, and my brother is looking at that surgery in his future. I hate to say it because it seems so contrary to what you want to believe, but I do think that after knee surgery you do have to take care of your knees pretty much for the rest of your life. It doesn't mean you have to stop being active, but you have to think about long-term mobility and activity and weigh the benefits of being a daredevil now against what you would like to be able to do in ten, twenty, thirty years.

Fortunately cycling seems to be good for knees, although maybe you need to embrace the lower gears on the hills!