Background: The intraoperative mortality and overall complication rate for gluteal augmentation with fat transplantation is unacceptably high. The current controversy among experts regarding safety is whether fat should be placed within the gluteus muscle or limited to only the subcutaneous space. The purpose of the present study was to test the hypothesis that under certain pressures, fat injected within the gluteal muscle can actually migrate out of the muscle and into a deeper plane containing critical neurovascular structures, by means of the process of deep intramuscular migration. Methods: A total of eight human cadaver dissections were performed. Four hemibuttocks were selected for intramuscular fat injection. The patterns of subfascial fat migration were evaluated in three of these hemibuttocks by direct visual inspection and in one hemibuttock by endoscopic evaluation. Four other hemibuttocks were selected for subcutaneous or suprafascial fat injection. Results: Proxy fat was found to migrate through the muscle and into the deep submuscular space with each intramuscular injection. With subcutaneous injection, no proxy fat was found during dissection in the intramuscular septae or submuscular space. Conclusions: The intramuscular insertion of fat, which up to this point has been considered reasonable to perform in the superficial muscle and even recommended in the literature, is now deemed to be an inexact and risky surgical technique. This technique, because of the migratory nature of injected fat, should be avoided from further use in fat transplantation to the gluteal region.
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