5 Years after Hip Replacement Surgery soreness and limping

My 88 year old Mother had hip replacement surgery years ago. She had one hip done which turned out good. The other one never really did good as she started complaining about stiffness and something way down deep in the bone. The doctor told her it widget better, but it never did. Years later she is limping and complaining about soreness. I took her back to the surgeon who x-rayed the hip and didn't see anything. It's hard for me to see her limping around and holding her hip. Wondering if anyone has any suggestions on what this might be or what I can do to help her?