The Center Cartilage At The Lower Right Front Of Chest

The center cartilage at the lower right front of chest seems to detach and roll up. It feels like a small fist pushing out, and can be manipulated back into place. Very painful when it happens and getting it back, although I can't figure out what triggers it, so I can not just show the Doctors. X-rays over the years show no abnormalities so I have nothing but pictures and a short video to show. I've been seeing Doctors for years and nobody can give me a proper diagnosis