What procedures can permanently fix the space between high hips and buttocks (hip dips)? (Photos)

 Are there synthetic filler options? I have the problem of high hips or "hip dips" as people call them. There is an indentation in my sides between my buttocks and my protruding hips and it usually worsens with weight gain. What procedures are available. Are there synthetic fillers other than fat? If I were to get a fat graft to give myself smooth sides, would weight gain or loss affect the results later? Would the "hip dips" return?