Loose bone fragment Post-BHR?

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My 6 month xray is showing a possibility of a loose bone fragment. It looked like a piece of bone was there in the previous xray, that is no longer there. The fragment didn't show up elsewhere so maybe it is hiding.

I felt a "pop" sensation 3 weeks ago, then had on and off pain and a return of the initial post surgery "catching" and "clunking" sensations, while also having a mysterious INCREASE in range of motion.  The pain has started to subside and I haven't had any intense pain jolts for 5 days now, so my surgeon didn't seem at all concerned about what might have happened or that it would present any problems.

Anyone ever hear of something like this? He didn't seem sure, just a theory, and had never seen or heard of symptoms like this before. I'll try not to worry about it but it begs the question of why that bone fragment was still there to be "broken" off to begin with.