Gluteal injections?

I have heard that many women, especially "video girls" have taken to receiving injections to increase the size of their ocks. This is seemingly a popular procedure kept quiet for a while. I knew when I saw women whose ethnicity is not really known for their larger backsides that either there was science involved or the had definitely been eating their Wheaties! (lol) But on a more serious note, I would like to get more information on this subject but can't seem to find anything through a search engine otehr than birth control methods. What exactly is the procedure for these " shots"?