The buttocks is a very interesting area of the body. If you suck the fat out, the butt will deflate and hang lower, but the crease will not change. If you put fat into the butt, this will give you a buttocks lift of the deflated skin, but the crease will not change. When buttocks creases are at two different levels, surgical intervention to create a new crease at a higher location and not fat grafting will correct the problem.
An ellipse approximately 3-1/2" long incorporating about 1/2" of the bottom of the buttocks, and 1/2" - 3/4" on the posterior thigh can elevate a low hanging crease when permanent sutures are placed from the SFS to the ishial tuberosity (the permanent suture pulls the fat below the dermis up to the bones at the bottom of the butt), and curves the tissue of the buttocks in to create a new crease. Usually, about 3 permanent sutures are used to create this crease. The resulting scar, if sutured correctly, is usually favorable because it is thin and well hidden in the crease.
This is, in fact, not an unusual situation. The surgery used to correct this problem is a combination of the work of both Ted Lockwood, M.D. of Kansas City and Louis Toledo, M.D. of San Paulo, Brazil.
Obviously, this surgery is for professionals well trained in body lifting techniques. Consult a Board Certified plastic surgeon with the aforesaid credentials.