I feel for you, I’m in the same boat. The answer to your initial question is: no one knows. Even the greatest surgeons or PTs can’t know everything that goes on inside you. It is probably muscular, and hours of stretching/PT may fix it; give it a shot. It might be prosthetic; X-rays and MRI does not reveal every variable, so they may say “nothing wrong”, but there are always those cases….. Look at it from a risk/reward perspective. Will stretching/PT hurt me in the long run; nope. Will running through the pain disturb the prosthetic? Maybe, maybe not. I’m resigned to hiking and mountain biking and having zero pain. Would rather run, but a man must know his own limitations. Good Luck.