What Is The Painless And Long Indentation On The Outer Part Of Leg?

Today we noticed an indentation about 3 inches long on the "outside" of my wife's lower right leg,. It is several inches above the scar left from having her broken ankle fixed with 5 screws several years ago... however it doesn't seem to have any positional relation to that. It is not sore to the touch, nor causing any pain. The other leg is normal.



What might be the cause?