I asked a question similar to this a few months ago IIRC. Most of the replies I received were all for the knee replacement, even though my ortho wants me to put it off until the point of no return (I’m in my early 50s, which conservatively is considered too young for such).
I’ve had to scale back my activities to an extent. At the gym, for instance, I can only use the bike, and it helps not to do it for long stretches – let’s say pedal for 15 minutes, then do a partial Nautilus circuit, then go back to the bike for another 15 minutes, then another partial Nautilus circuit, that sort of thing. I’ve also revived some of the exercises I did back in PT. Leg lifts have helped the most. I’ve got very tight quads/hamstrings from standing 8+ hours at work every day. They’re still tight, but obviously not as tight as before because my knee pain has diminished a bit.
But yeah, ultimately I’m going to have to have a knee replacement at some point.