What Causes The Dents On The Thighs?

I HAVE HAD A DENT IN MY UPPER THIGH FOR EVER I BELIEVE MY WHOLE LIFE AND OVER THE WEEKEND MY COUSIN NOTICED IT AND SAID SHE HAS THE SAME THING BUT BOTH OF US HAS NO CLUE WHAT IT IS, OR HOW WE GOT IT. ITS IN MY RIGHT UPPER THIGH ABOUT 3 INCHES UP FROM MY KNEE AND THE DENT GOES IN JUST A LITTLE , BUT VERY NOTICEIABLE , AND ABOUT AS ROUND AS A HALF DOLLAR DO U HAVE ANY CLUE WHAT THIS IS OR HOW TO GET RID OF IT , OR HOW I GOT IT????????????????????