In the 1990s, buttock lipoaugmentation9 was dismissed as a simple operation requiring no special instrumentation10 and was considered a questionable procedure. Lack of adoption was fueled by lack of results, because of the inability to accurately quantify volume.11,12 Despite its popularity, the classic Coleman technique for fat grafting to the buttocks may not result in an effective or efficient operation. By wedging microdroplets of fat on axial withdrawal of a 12- to 14-gauge cannula, recipient-site interstitial pressures may rise quickly, setting limitations on graft volumes. Furthermore, this technique does not affect significant recipient-site shape change. Power-assisted equalization of the recipient site was first described by Wall,13,14 followed by recent reports of a syringed-based technique.15
Expansion Vibration Lipofilling Considerations
Expansion vibration lipofilling allows for recipient-site expansion by using exploded-tip injection cannulas, creating a wider potential space and ability to separate and equalize tissue. Concurrently, fat is deposited into the expanded area with the exploded-tip cannula, effectively serving as a stent followed by the immediate deposition of graft to occupy the stented space. The exploded portion of the cannula, typically two times the diameter of a typical 4-mm cannula, creates four times more space as it moves through the target zone (using πr2). In addition, recipient-site expansion grafting is also significantly enhanced by the use of vibration (reciprocation) of the cannula, as the differential pressure zones created by the exploded “wings” of the cannula are magnified by movement (vibration).
From the steps learned in SAFELipo, expansion vibration lipofilling can be envisioned as a logical extension of “equalization” of the recipient site during fat transplantation. In an abundance or excess of graft, as is seen during lipofilling with exploded-tip cannulas, oscillations allow homogeneous distribution of fat lobules. Angled cannulas, rapid oscillations, larger diameters, and quicker flow rates allow for further “reach” of the cannula, resulting in more extensive and thorough equalization of recipient-site tissue, analogous to spray painting versus painting with a brush. More thorough and dispersed fat translates to more surface area contact between grafted fat lobules and recipient tissue.
Role of Expansion in Lipofilling: Aesthetic Sequelae
Fat cells are subject to shear injury16 and do not act as tissue expanders to expand constricted areas. The classic Coleman technique involves the injectional wedging of fat into recipient sites, as “microdroplets,17 without active expansion of the recipient site per se. Therefore, fat injected into depressed concavities using the Coleman technique can traverse to areas of lower resistance, failing to improve contour deformities. In most cases, the deformity is not treated, and surrounding areas with greater tissue compliance receive the fat, resulting in additional deformities.
We define the “tombstone deformity” as a classic example of inadequate release and expansion of the midlateral buttock hollow, associated with fat transplantation to the buttocks using syringe-based techniques. Unless this area is aggressively expanded and backfilled with fat, fat simply injected into this area will cause fat to migrate, most commonly superolaterally, to the hip area, resulting in a square buttock shape, or the tombstone deformity (Fig. 10).
In the classic Coleman technique, fat is inserted using small-gauge needles, wedged into existing tissue without any disruption of the recipient-site architecture. This puts pressure on adipocyte lobules and limits the expansion of the volume of the recipient site. In this scenario, adipocytes are asked to play the role of tissue expanders, finding a blood supply and at the same time surviving by diffusion. What may make sense in lower volume, higher compliance situations such as the deflated aging face simply do not make sense in large-volume recipient sites such as the buttock. Although we have previously articulated the differences between small-volume and large-volume fat transplantation,18 we make the further distinction here with regard to the restoration of volume lost, which is a completely different recipient site from the augmentation of volume that never existed (Fig. 11).
Apart from the aforementioned aesthetic limitations of nonexpansion syringe-based techniques in large-volume fat transplantation, there may be serious safety issues in buttock fat grafting.19,20 Description of deaths caused by fat embolism21 were reported in conjunction with nine cases of large-volume fat transplantation, all using syringe-based lipoinjection. In this article, the recommendation of the author, and follow-on letters to the editor,22 were to “use only blunt cannulas 3 mm in diameter attached to low-pressure syringes.”
To achieve fat emboli on this macroscopic basis, fat must enter the venous system in a significant volume as to obstruct critical segments of the cardiopulmonary circulation. We posit two mechanisms for achieving this:
- Cannulation injection theory: A significant sized vein, such as the superior gluteal vein, is directly cannulated as a large bolus of fat is actively injected into the venous system.
- Laceration siphon theory: Injury to a large vein occurs because of direct venipuncture or indirect tearing, and ensuing high-pressure fat passively flows into the lower pressure venous system over time, as more fat is transplanted.
Although both theories are possible, laceration/siphon seems more plausible because of the constant movement of a cannula during lipoinjection, which would make cannulation/injection less likely. To summarize, the two conditions necessary for a fat embolism are venous injury and a high-pressure state.
Therefore, to reduce or eliminate the risk of fat embolism, one must eliminate one of the two causal factors above. Because it is not possible to eliminate high-pressure states during fat transfer, the only certain way to avoid the risk of fat embolism is to avoid venous injury during fat transplantation.
Avoidance of venous injury requires two key components: a complete understanding of the anatomy and a complete knowledge of where the tip of the cannula is in relation to these veins—at all times. Although the first is relatively easy to learn, the latter is often not possible because of “flexibility misguidance.”
Reduction in extremity proprioception with muscular fatigue has been well documented in the orthopedic literature.23,24 During syringe-based grafting, surgeons rely on their operating extremity to simultaneously perform three critical neurologic functions: (1) axial “back-and-forth” motion by shoulder and elbow muscles; (2) propulsion of syringe flow using hand intrinsic muscles; and (3) sensory proprioception of the cannula tip’s location. Sometimes, both hands are manipulating the syringe during injection, further decreasing proprioceptive feedback of the location of the cannula. A flexible cannula, such as a 14- or 16-gauge cannula, can be subject to deformational bend on encountering resistant tissue. On axial penetration, a slight bend in a flexible cannula, or instability in its cannula/syringe (Luer-Lok; Becton, Dickinson & Co., Franklin Lakes, N.J.) junction will continue to curve in the direction of the bend, leading to deeper and deeper tissue planes despite a superficial orientation of the syringe by the operating surgeon. We define this as flexibility misguidance which, in addition to muscular fatigue, may explain why some surgeons actually inject deeper than they intend to or deeper than they think.
In contrast, peristaltic pump-propulsion of fat in expansion vibration lipofilling eliminates the need for hand intrinsics. Vibration through tissue minimizes or eliminates the need for forceful axial back-and-forth arm motion, allowing the surgeon to concentrate solely on the tactile feedback of the cannula tip and its location in the recipient-site tissue. In no cases of known or reported fat embolism during large-volume fat transplantation to the buttocks to date has the technique of expansion vibration lipofilling been used (Fig. 12).
The use of a rigid, larger diameter (4 to 5 mm), vibrating, exploding-tip cannula when grafting fat to the buttock theoretically provides six distinct potential advantages. First, the exploded tip provides acute expansion of the recipient-site space, allowing fat to be deposited with less interstitial pressure. Second, the three or four large holes of the exploded tip provide an acute increase in surface area for fat to egress, reducing intraluminal flow pressure and drag. Third, the larger diameter of the cannula makes its larger, blunter tip less likely to perforate a venous structure. Fourth, its stiffer nature promotes deliberate directional grafting and minimizes or eliminates flexibility misadventure seen in smaller gauge cannulas. Fifth, a fixed-angle cannula can be rotated to increase cannula excursion and efficiency using fewer passes, and also allows it to be oriented superficially to minimize deeper tissue penetration. Finally, the vibrational effect allows for better tissue penetration with less axial pressure and force without the tissue trauma of higher energy devices.25
Power-assisted liposuction devices were introduced 20 years ago for liposuction. They were never described to propel fat in fat transplantation. The off-label use of these oscillatory devices is hereby recognized, as is the use of lobules of fat on the order of 1 to 4 mm in diameter, which are directly a function of the hole size of the harvesting cannulas used. Although the size of these fat lobules violates the “2-mm rule,” first described as the largest lobular size of fat that could survive by diffusion and imbibition of oxygen,26,27 in a practical sense, fat lobular sizes in this series of patients ranged from 500 μm to over 4 mm, and the long-term volumetric results do not evidence significant cases of clinical fat necrosis.
Fat grafting to the buttocks, once thought to be a simple operation, is emerging as a series of sophisticated maneuvers, each of which requires proper instrumentation, techniques, and operative strategies, including respect for deep anatomical structures and proper patient positioning. The most optimal maneuvers for buttock fat transplantation may not be the same as those we have seen to be so useful in the face.
In the classic fat transplantation triad of donor harvest, processing of graft, and the transplantation event, great investment in intellectual property, investment capital, and marketing efforts have been made in technology-rich harvesting systems and fat-processing systems. Meanwhile, little technological innovation has been made in the transplantation of fat or in postgraft shaping. This is partly because of the industry’s focus on high-price-point disposables that can be marketed through existing distribution channels, the lack of clinical awareness on the part of those who design and conceptualize fat technologies, and physicians who help promote them.
We define expansion vibration lipofilling as a new technique using existing instrumentation in an off-label and novel way to achieve better volume control and shape change in large-volume fat transplantation. As such, expansion vibration lipofilling better fits our emerging understanding of volume increase and shape change when using fat in aesthetic surgery. Presuming this technique is adopted for large-volume fat transplantation, larger case numbers are required to ultimately help define its safety. For the present time, anatomy, avoidance of vital structures, instrumentation, and technique appear to be the greatest factors in safety and efficacy.
Patient provided written consent for the use of patient’s images.
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