No infections were encountered. No patient developed symptoms or signs of fat necrosis, and no evidence of fat necrosis was detected on the ultrasound examinations. There were no seromas or hematomas. There were no cases of fat embolism. No deep venous thromboses were detected on any of the ultrasound examinations. No patient required hospitalization or a blood transfusion. All patients were treated with fat injection once. No patient underwent reoperation. There were no cases of sciatic neuropathy or painful paresthesias. There were also no complications among the 4 treated patients who did not return to follow up at least 3 months after surgery and therefore did not meet the study inclusion criteria.
Buttock augmentation was originally accomplished using silicone implants.2,12,13 However, the complication rate is very high (38.1% among surveyed surgeons16).2,12,13 Because of its lower risk, fat injection is more commonly performed by plastic surgeons than buttock implants.1
The patient is not paralyzed or intubated. Instead, a laryngeal mask airway is used and the patient breathes spontaneously.10 This airway has proved to be safe with the patient in the lateral position, provided it is secured using tape. In a departure from traditional prone patient positioning,2,8,14–16 the author never uses prone positioning for liposuction or lipoinjection or any other procedure.
Previous studies report mean injection volumes in the range of 350–700 mL per buttock.14–19 Some investigators use aggressive liposuction in an effort to obtain more fat for grafting.2,17 However, aggressive liposuction increases the risk of wound complications, such as seromas.2,15,17 Murillo,17 who injects an average of 700 mL fat per buttock, reports a donor site (abdomen and sacrum) seroma rate of 40%. Drains may be needed.2,8,17 Painful paresthesias of the flanks and gluteal regions are sometimes encountered.16,19 Contour irregularities may occur, especially in thin women.
Recently, concern has been raised regarding the risk of fat emboli after buttock fat injection.20 Cárdenas-Camarena et al20 recommend keeping the injection cannula parallel to the gluteal surface to avoid entering the subpiriformis or suprapiriformis channels where the gluteal vessels are located. Intramuscular fat injection was once preferred.2,14,18,19 However, recent investigators have injected the subcutaneous plane instead.16 No incision is made in the gluteal fold so as to avoid neurovascular injury. Injection in multiple tunnels is a well-known measure2,8,15,16 to maximize fat vascularization.
The use of 60-mL syringes may be challenged by surgeons who believe that too much fat is injected in each pass of the infusion cannula. This concern is based on the work of Carpaneda and Ribeiro,21,22 who report that greater fat necrosis is likely if fat is injected in tunnels that exceed a diameter of 3 mm. Shear stress is minimized by using large infusion cannulae,23 which are less likely to impair adipocyte viability.24,25
Centrifugation is cumbersome and time-consuming, especially for large fat volumes.2 Smith et al26 report no advantage in cell viability from washing the fat or centrifuging it and recommend against unnecessary manipulation or delayed reinjection. Gerth et al27 report that a closed-membrane filtration system provides greater fat retention than centrifuged fat when injected in the face. Fisher et al28 report that both filtration (using the same Filtron device used in this study) and centrifugation effectively remove fluid fractions and result in comparable graft retention, with minimal loss of the stromal vascular fraction in the discarded filtrate. Any fat that passes through the filter seems to have negligible viability.28
Despite theoretical concerns about fat necrosis using large syringes and cannulae to inject fat, there were no clinical cases of fat necrosis in this series. Moreover, there was no evidence of fat necrosis on the ultrasound scans, which are highly sensitive for the detection of oily cysts caused by fat necrosis.29 Although early investigators used 3-mL syringes,18 the time commitment was substantial (eg, 2–4 hours for harvesting plus 1–1.5 hours for injection18). In the past decade, most plastic surgeons2,8,14–16 have adopted 60-mL syringes for large-volume fat transfer.
The dilution of the lipoaspirate is variable, depending on whether a superwet (1:1 ratio) or tumescent (3:1 ratio) is used.10 The supranatant typically represents 40–50% of the lipoaspirate volume.2,18 Recognizing that fluid is injected with fat, some operators recommend overcorrection.16,19 However, Del Vecchio and Del Vecchio30 caution that higher graft-to-capacity ratios can reduce volume maintenance (fat retention). A superwet infusion and a filtration system that separates the fat from the wetting solution may account for the relatively small lipoinjection volumes used in this study. Moreover, for many patients, buttock fat transfer was not their main objective but rather an adjunctive procedure. If offered the option, many patients elect to have some fat obtained by liposuction injected in their buttocks, even if only an incremental benefit is expected.
Using closed filtration, buttock fat transfer typically adds no more than 20 minutes to a liposuction procedure. The efficient use of operating time lowers the cost and permits the procedure to be done in conjunction with other body-contouring procedures including breast surgery and abdominoplasty. (See Video 1, Supplemental Digital Content 1, which demonstrates injection of the local anesthetic, fat harvesting, and fat injection. This video is available in the “Related Videos” section of the Full-Text article on PRSGlobalOpen.com or available at http://links.lww.com/PRSGO/A198).8,14
Although several studies provide clinical data and subjective evaluation of buttock fat transfer,2,8,14–18 objective measurements are lacking. Murillo17 used magnetic resonance imaging to document a qualitative increase in buttock fullness in 6 patients undergoing intramuscular buttock fat injection. Magnetic resonance imaging was also used by Wolf et al14 in a quantitative study of 10 patients undergoing gluteal muscle injection, but only muscle areas were measured, not subcutaneous fat thickness, despite fat injection in both locations. Neither study14,17 controlled for postoperative changes in body mass index.
Magnetic resonance imaging is prohibitively inconvenient and expensive to use in a large number of patients. Ultrasound examinations are more practical and were already being administered to these patients as part of surveillance for deep venous thromboses. A minimum follow-up time of 3 months was selected based on previous studies of fat injection31,32 using magnetic resonance imaging that reveal little change in the fat layer thickness beyond 3 months, suggesting that swelling has resolved at that time.
The clinical safety of buttock fat transfer stands in stark contrast to the high complication rate of buttock implants.12 Importantly, all the patients in this study had areas of excess adiposity available as donor sites. An increase in fat thickness of <1 cm is admittedly modest but complemented by fat reduction of the flanks, as demonstrated by the increase in relative buttock projection. Even if fat retention was 100%, one could expect only about 1 cm of increased projection from 287 mL fat distributed over an area of 250 cm2. Accepting a lesser degree of augmentation may be preferable to donor site deformities, seromas, and paresthesias caused by overly aggressive harvesting.
Only 1 surgical method and 1 type of fat collection device were studied. Other techniques and devices may produce different results. The size of the treatment group (n = 21) is relatively small. No information is available regarding possible changes in fat thickness occurring at longer follow-up times (eg, >1 year). One-dimensional fat thickness measurements do not assess volume changes. Future studies may incorporate 3-dimensional imaging methods. This study provides quantitative evidence of the efficacy of buttock fat transfer using a reliable diagnostic tool corroborated by simultaneous photometric data. By measuring patient weights before and after surgery, a change in body mass index is ruled out as a possible confounding variable. Consecutive patients and a high inclusion rate add to the reliability of the findings. The prospective study design and inclusion of a control group achieve a high level of evidence.
Comparisons of matched photographs and ultrasound measurements may be used to evaluate changes in buttock fat thickness. Buttock fat transfer effectively and safely increases buttock projection.
I thank Jane Zagorski, PhD, for statistical analyses, Christina Engel, RT, RVT, RDMS, for ultrasound studies, Sarah Maxwell, RN, for data collection, and Gwendolyn Godfrey for the illustration.
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Supplemental Digital Content
Copyright © 2016 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the American Society of Plastic Surgeons. All rights reserved.