Why continuing pain three years after a successful hip replacement?

My wife had a hip replacement three years ago. The surgery was, by all measures, successful. Yet it became painful starting after three months and the pain has gotten worse. All kinds of treatments have been tried, including physical therapy, steroid injections. The implant has been examined by the surgeon and by other orthopedists. No one can find the cause of the pain. A Mayo post by Liza Torborg has suggested three possible causes: infection; a loose ball in the socket;; and psao tendinitis . The first two have been ruled out. What specialist at Mayo Clinic can diagnose the third possibility?