It is very difficult to determine the exact size and shape implant you will require to best match your ideal butt image without an examination by a board certified plastic surgeon. Not just any board certified plastic surgeon, but one with many years of frequently performing breast augmentation...
Depending where the implants are put, they may drop in time specially if put in subcutaneous position. If they were put under the muscle the chances are much less that the implant will drop if put right.You may need revision surgery.
Arian Mowlavi, MD, FACS (license on probation) says:
No, eurosilicone is not safe for buttock implantation. The only silicone that is safe to place is the buttocks is enblock as an implant. Small aliquots of silicone when injected will create sever scarring, infection, and silicone extrusion.