Don,
I can't give you much more on knee replacement than anyone else here has given you, but I've seen a number of them since I've both hips replaced (a big piece of why I haven't been around here much). Most people are far better off after the replacements IF they do do the PT. I knew from falling off the FZ1 in 2004 that PT needs to be attacked with abandon. I call it "Treat PT like it's an enemy you have to defeat and destroy!" Push as hard as you can--you want your therapist to be telling you to slow down or do it easier, not egging you on to work harder and push more. Then be prepared to baby it. No running, no martial arts, never high impact. That doesn't mean you can't work out and work out hard! I do. The two guys I know who have NOT had success with their knees, BOTH worked outdoors. One runs a landscape business and even the revision (official term for re-doing a replacement) gives him a lot of pain. The other was the best sprinkler tech I've ever seen--and was on his knees all day, even after the surgery. Oh--there was a lady, very heavy, who, in the PT room with me (after my 2nd hip) who looked like she was never going to be OK because she didn't want to do the exercises--they HURT but you just have to put that aside.
How will you know when to do it? Well, every doctor says, and I agree, "You'll just know!" And you will!
For me, I was in agony with my left hip and walking on a cane when I went to the doc I SHOULD have used for both hips. I didn't know it, but my right, despite no pain, was nearly as bad as the left. After not being able to walk much on a vacation, and struggling to keep the house powered during the blackout of the Halloween "FrankenBlizzard" of 2011, my family said "Do it!" I ended up with a different doc, at the hospital that does all the NY Jets surgeries, and he's done 4000 hips. He had been AMAZING with my back pain, giving me exercises nobody else could that worked. Yet.....
So I committed myself to losing weight--almost 40 lbs, doing lots of cardio (swimming and arm bicycle--couldn't use a treadmill, bicycle, etc) and a TON of upper body work just in case I had to carry myself with my arms. Lucky I did....The surgery went smoothly and the next day I was walking on it. Then they moved it around and, I let out a yelp. I couldn't walk on it, but they didn't x-ray it, instead, sending me to a stepdown rehab where I spent the next 12 days. NOBODY thought to take a simple, no-brainer X-Ray, either before I left the hospital or at the rehab. I went back to the doctor for the 2 week followup. They X-rayed it routinely...it had been dislocated for nearly 2 weeks and I was going through PT with it! I kept asking "How come it hurts so friggin' much? How come I can't put weight on it?" I was back in surgery that night for a "reduction" of the dislocation (no cutting needed). I was able to stand the next morning. But now the soft tissue was all stretched and damaged, so PT was very painful. But I kept at for 2 months before going back to the gym. More and more exercise worked it out but it still flairs up 4 years later. My wife investigated a malpractice suit but no lawyer would call her back. DESPITE that, I'm still far better off than I was before the surgery and I'd STILL go through it again if I had to!
After about 2 years the right hip was now hurting like hell. Between it being "cartilage free" for years and the left being just about 1/4" longer, i couldn't sleep. So I went to the doc I SHOULD have stuck with, at a fine, but less prestigious hospital. This went FAR better. For a month after I had a lot of pain, and lived on ice and pain-killers. Weirdly, my right knee hurt like hell and I wondered if I had damaged it. Nope. It was just temporary. The physical therapist came to the house for about 5 visits, then I went right to the gym. I've been great because I kept up the exercise and there were no "adverse events". Now, 2 years later, the difference in leg length gone, the right rarely gives me even a twinge. It's not that I skimped on PT, it's that I did it myself having been through it already.
Do not let anyone talk you into a metal-to-metal joint. Now the liner for hips and knees is irradiated cross-linked polyethelene, whatever that is, that wears far more slowly than previous liners. 15 years was the AVERAGE life, but now most are expected to last ON AVERAGE 20 years. But you must become and stay active.
And you'll NEVER go through a metal detector again without setting it off. So ask them to put you through the body scanner and it's much faster!
YT