Hi sapper1ID and welcome to ehealth: I am not sure what it is called other than a "flotating bone fragment"...However, I can tell you that our son had two of these in his left knee and seeing he was a pitcher had to have them surgically removed...They were called partial fragments of his knee cap...His was because the knee cap was not fully matured and these were like pieces of it that never meshed...He did have surgery when he was 18 to have them taken out...I believe your pain will dictate what you have done...Good luck and take care...
Caroline