I have no personal experience with this except my wife had a triple fusion at the L3 through L5 which included rebuilding at least one of the vertebrae with a mix of her bone and cadaver bone. She also had a nerve root pinched for which they augered out the arthritis to stop the pinch. She had that done in June 2023.

She still sleeps in a recliner because the back can't handle the bed - still does PT and is now doing a senior exercise class to rebuild strength. She actually moves pretty well though.

I suspect (and I think your pain management specialist does also) that there's still something possibly orthopedic that's causing the ongoing pain. It might be worthwhile to have an orthopedic specialist look further if you haven't done so already

Sorry for your situation. Wish I had better ideas.