Hello Donkey,
Your posting sounds like my situation. I can't say that my experience will work for you but you asked for ideas where you could proceed. I had a TKR on my right knee in September 2018. Generalized pain continued subsequent and all the surgeon could say was that the knee looked good on xrays. Finally, I found Dr. Fred Cushner at HSS, who required a referral, and I went to NYC in 2020. He agreed that the knee looked good but recommended my surgeon "look" at my back. An MRI found stenosis in my lumbar spine. I was told repeatedly that "this is a very odd presentation", but I had injections which worked for two years to alleviate the pain. I was warned that the injections wouldn't work indefinitely. Now I have a spinal cord stimulator.