I had avascular necrosis (AVN) of both hips. The term literally means, "bone death."
AVN is when the blood supply is cut off to the top of the femur near the hip joint. The bone dies and begins to crumble. The pain is unbelievable.
This condition is non-reversable. The only solution is "core decompression" if caught early, or hip replacement. My situation progressed quickly, so bilateral hip replacements and gastric bypass to drop a lot of weight fast, were the methods my orthopedic surgeon decided were in my best interest.
AVN requires open communication between you and your doctors. Ask a lot of questions. See if you are in the early stages and capable of employing early intervention methods.
Best wishes to you.