Why aren't tissue expanders used for butt implant surgeries? Not inside the muscle, but I mean near the incision area?

Tissue expanders are not of any particular benefit for buttock implants. Not only is there no cost savings, with tissue expanders often more expensive than actual implants, but there is also no savings in the time required to obtain an otherwise oversized implant. Whether done traditional or with a tissue expander, two surgeries are required to get to the larger implant. With traditional, the patient can enjoy the results of the implant for 6 months without intervention until returning for the upsized implant.  With tissue expanders, the patient must return to the surgeon weekly for 2-3+ months to have more saline fluid injected into the expanders before then another trip to the operating room is necessary to remove the expander and put in the actual implant.  This process tends to be much more labor intensive with all these trips back and forth to the surgeons office.  Additionally, the overall complication rate, extrusion in particular, tends to be significantly higher for tissue expanders in this area of the body.  Finally, tissue expanders are typically round and will not create the anatomically correct pocket for an anatomically correct implant such as the Stanton Anatomic buttock implant.  hope this helps. 

Dear Miss Congeniality Too,
butt implants have a high rate of complications and I avoid using them Fat transfer is much better option to increase the size and projection of buttocks. If you are considering a surgery, I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.
Daniel Barrett, MD

Very astute question and I have been placing tissue expanders for butt augmentation. I still definitely prefer to use BBL procedure but when there is not enough fat to get to inject and the patient wants a large butt, I place an expander but within the gluteus muscle. Then after about 4 weeks the patient can start expanding to whatever size they want. Some of my patient keep the expanders in place but others then opt to place a permanent silicone implant of whatever size I have expanded it. In the intial surgery it is not feasible to place very large implants for there is not enough room.