I had my right knee replaced in July, 2011. That was my seventh surgery on that knee, four by arthro, two by incision back in the day, and an ACL replacement in 2000. This year I did five triathlons, including two Olympic distance. But I walk the run part. I ride several times a week, and my wife and I have a brand new tandem (our second one) that we ride once or twice a week.
My farthest walking/race distance to date has been 8 miles in a bit under two hours. I'm hoping to get a half-marathon this year.
Here's a big key to knee replacement that most therapists won't tell you........
if, after surgery, you can't get the leg to zero degree extension, or even better is a few degrees of hyperextension........YOU CAN NEVER WALK WITHOUT A LIMP. You have to be able to get that leg fully straight or else it will always be shorter than the other when you walk. If you walk with a limp, the rest of the muscular and skeletal system starts trying to compensate. That is the cause of the resultant back and sciatic pain for most folks.
Ever see someone who had a knee replaced and when they walk it looks like they have a spring in their shoe?
As to the timing...the time to do it is when the bad knee keeps you from living a normal life, or else you can't stand the pain.
Before surgery, take a few months with a trainer and get the weight down and the leg as strong as possible. You can generally do squats with a bad knee once you get the strength up. How is this possible? When the knee is bent, as in squats, generally the "good part" of the knee joint around the edges of the femur-to-fibula joint is doing the work rather than the core of the knee.
Here is the BEFORE, looking from the front. That's the right knee that's crooked, and you can see the ACL transplant screw.
Here are the after shots.
