I had an injection which didn't help for long, then an arthroscopy where they scrape out all the random floating bits of cartilage. That gave me about three years before it got so bad again that I couldn't walk well at all. For me, it wasn't so much the pain as my knees were collapsing inwards so there wasn't too much friction. I just couldn't walk and they kept giving way (you get points for that). In the end I paid for a private consultation and then used my future care home fund to pay for the first one and got the second done on the NHS (I was advised to pick a surgeon who did NHS work too), so a sort of BOGOF. That's the "step ladder". Physio is just the first rung.
It is a very, very painful operation to recover from and takes a good while. I know people who've had one done but then not wanted to face having the second one, so really haven't gained much as they still can't walk. You'll never get back the mobility of youth. I still have some discomfort from my knee caps if I've been sitting for a while and kneeling is a brief exercise when on hard ground! Also, it took well over a year before I stood any chance of being able to bend my ankle and knee to peddle a bike. I'm now working on ankle bend and balance exercises although I shan't bike again as I don't feel safe.
But, I can now walk several miles, swim, climb hills and clamber around up ladders and on boats, and have sat on a horse again. All things I'd not been able to do before. I could probably do more but I'm lax on exercising to get the leg muscles back working as they should.
Hope this helps.