Thirty years ago I was in a lot of pain as I had no cartilage in one side of my knee, due to an accident. Back then I was told I needed a knee replacement, but they wouldnt do and said I was too young. However after struggling on for years I got to the point where I ended up on crutches due the pain. So it was 5 years ago I had it done. For me it was unbelieveable. The day I left hospital the physio said she would have me walking a mile within a month. I said I hadnt walked a mile in the past 25 years. Believe it or not I walked my first mile on day 2 after the op.
Yes I did need the pain killers like oxi contin and oxi norm, but after my first visit to physio they told me not to bother going back. I am working reduced hours at work now and only cover around 10 miles a day, but a year ago I always walked more than 15 miles a day. Not bad at all for someone who previously couldn't walk at all.
It has just gone on to get better and better, I have no thought or feeling about it not being my knee. I can kneel on concrete without hesitation, the only thing I back away from, is very heavy lifting.
Having spent years working with the disabled I can relate to their being many people who wish they had not had their knee done, but in my case, no regrets.
One bit of advice after the op would be to get your favourite chair and a sleeping bag and live in the chair day and night until you get more mobile.
Good luck !