Just taken my cat to the vet today and he has arthritis 
He's had an on off limp for a month or two so I suspected, but yesterday he was in pain so we've taken him in.
He had luxating platellas (roaming knee caps) back when he was fat so it's probably been a product of that.
Unfortunately he has kidney/bladdet problems so vet is debating what anti inflamm/painkiller to put him on. Going to do a urine sample today see how they are currently functioning.
Poor puss 