Fat grafting involves transfer of nonvascularized, but viable, fat cells from one location to another within the same individual. Although fat grafting is generally successful in many circumstances, the results can be unpredictable in terms of volume maintenance. It does transfer fat and stroma in a single setting, although it usually requires multiple stages to achieve satisfactory clinical results, especially when larger contour defects are treated. Both mature adipocytes and preadipocytes can be transferred, but of the two cell types, preadipose cells are more resilient to ischemia and can continue to differentiate and proliferate after regaining a blood supply.1 Peer’s cell survival theory states that the number of viable adipocytes at the time of transplantation correlates with ultimate fat graft survival.2
One of the main advantages of fat transfer is its beneficial effects on irradiated skin and soft tissue. Although the precise mechanism is not fully understood, fat grafting can soften the skin and allow it to become more pliable. Skin complexion and scar appearance can also be improved. Histologic and electron micrographic evaluation after fat transfer shows progressive regeneration of tissue ultrastructure with a reduction in epidermal thickening, vascular density, and fibrosis. Often, after the first lipofilling procedure, improvements in skin appearance are the most obvious visible benefit. There is no evidence to suggest that tumor recurrence is affected by fat grafting. Concerns have been raised as to whether injection of stem cells places patients at an increased (not decreased) risk of developing further tumors, but this has not been substantiated. Some authors suggest that fat transfer may make tumor surveillance more difficult, rather than simple, due to microcalcification on mammogram, but it should not interfere with detection providing the evaluation is performed by an experienced radiologist. Moderate bruising and swelling to both donor and recipient sites are inevitable following fat grafting, so patients must be aware of this preoperatively.1–4
Use of fat injection (lipomodeling) for refining autologous breast reconstruction has become standard practice for many breast reconstructive surgeons, particularly for the correction of superior and medial pole deficiencies. Correction in this scenario is possible with fat transfer but will require multiple stages and achieving a perfect contour is challenging. The patient’s body habitus will affect outcome, and in thin patients obtaining sufficient volume for transfer can be a challenge. This is exacerbated by the fact that the anterior abdominal wall has already been harvested for the main flap, leaving little fat excess present in this area. Often the flanks are a useful source for fat harvest in these patients. Other suitable donor sites include the thighs and upper central abdomen. Because up to half of the transferred fat may not survive, it is standard practice to overcorrect defects in the operating room where possible. Quite large volumes of fat (200–300 cc) should be placed at multiple levels within the flap to improve graft take. External expansion with the Brava system is not routinely used in this scenario, although it does represent an uncommon option. It is most commonly indicated for use in primary breast augmentation where a combination of fat transfer and the Brava system may improve outcomes.1,2 Although fat transfer is a useful technique in revision reconstructive cases, its limitations must be recognized. Where large deformities are present, standard surgical approaches may be more helpful to inset or recontour the flap. In some cases, where the lateral defect is large, further flap reconstruction with a thoracodorsal artery perforator flap or partial latissimus dorsi (LD) flap may be indicated. A caveat of fat transfer is that fluctuations in weight will affect the recipient area. However, the same is also true of transferred vascularized tissues such as transverse rectus abdominis myocutaneous (TRAM) and deep inferior epigastric perforator (DIEP) flaps, so patients should be advised of this before surgery.3
Fat transfer has many advantages over synthetic fillers, including low material cost, ready availability, a natural appearance, excellent biocompatibility, permanence, low donor-site morbidity, and the ability to contour donor sites where required. In patients with HIV and subsequent lipodystrophy as a result of taking antiretroviral medications, there is often insufficient fat available for harvest, and these individuals might require a synthetic alternative filler. Some HIV patients can develop fat excess in the posterior neck (buffalo hump appearance) and central regions. In these cases, it may be possible to use these areas for harvest.1–3
Atraumatic harvesting, handling, and transfer of fat are key to maximizing fat cell viability during fat grafting. Consequently, minimizing pressure by using a large-bore cannula (e.g., 3, 4, or 5 mm) and low pressure should be beneficial. For this reason, the Coleman technique involves the use of 10-cc syringes for harvest. There is debate regarding the benefits of assisted techniques for fat harvest, such as power-assisted or ultrasound-assisted liposuction,1 and traditionally these had been associated with decreased viability of harvested fat. Some evidence has shown high levels of fat cell viability after harvest with ultrasound-assisted liposuction that was at least comparable with or possibly superior to manual harvest.2 That said, there is usually a larger oil layer when performing suction-assisted fat harvest, which suggests fat cell rupture has occurred. Fat cell viability also seems to correlate with the amount of shear trauma and liposuction circuit pressure. Fat cell rupture is thought to be in part caused by the forces applied while passing through the suction circuit.3,4 In practice, many surgeons still use suction-assisted liposuction for fat graft harvest especially in larger volume transfers, as this is far more efficient in these settings. Furthermore, there are now some systems that harvest and collect large volumes of fat within a closed system for direct reinjection. Use of a tumescent infiltrate with epinephrine or local anesthetic does not improve viability, although it can reduce bleeding and facilitate ease of harvest. Some evidence suggests that local anesthetics may actually decrease fat cell viability and should ideally be diluted to minimize this.3,5
The aim of fat processing after harvest is to remove unwanted fluid, cells, and debris from the lipoaspirate, while causing minimal damage to the fat cells. There are different techniques used to achieve this, including centrifugation, sedimentation, straining, rolling, and washing. Cotton gauze rolling has been reported as having the highest graft retention in vivo.1 This technique involves pouring the lipoaspirate from the syringe onto a nonstick absorbent gauze, which is then gently rolled with an instrument handle in order to remove aqueous and oil layers. A comparative study by Rose et al2 compared the other three main processing techniques (centrifugation, washing, and sedimentation) and showed that the number of viable fat cells maintained was highest when sedimentation was used. However, this team did not then assess the outcomes after injection with the different processing techniques. Whether this would translate into a clinical outcome benefit therefore remains unproven. Furthermore, although it may be the least traumatic method of fat processing, it does expose the aspirate to the air and is a relatively slow process which may not be helpful in clinical practice. Based on current clinical data, outcomes appear similar irrespective of processing technique; so, in your practice you should select the one you are most familiar with until stronger evidence is available.
There are a number of approaches to processing harvested fat during fat transfer surgery. The Coleman1 technique uses the centrifugation approach. Centrifugation involves spinning fat in small syringes at speeds of approximately 3000 rpm for up to 3 minutes. This process will separate the harvest into three layers: top (oil), middle (fat cells), and bottom (blood/infiltrate). The middle layer must therefore be kept, as this represents the fat used for grafting. Centrifugation for longer than this is not recommended, as further separation does not occur and fat cells may be damaged. When using a washing technique, a number of different solutions may be used including normal saline, 5% glucose, or sterile water. Given the available evidence, saline is preferred compared with water and is common practice. In theory, washing cells in sterile water risks causing cell lysis because of the osmolarity difference. This difference is traditionally related to red blood cells but may also apply to fat cells. Rubin and Hoefflin2 have an interesting and somewhat controversial “survival of the fittest “ view on fat preparation. They use sterile water to wash the fat preparation and combine this with centrifugation at 6000 rpm, reporting satisfactory clinical results. They believe that stressing fat cells before injection results in only the most resilient cells reaching the injection stage. In general, most authorities work to minimize trauma to the fat cells (not increase it) during processing and this would be a more conventional approach. Sedimentation, decanting, and straining are not part of the Coleman technique, but are thought to represent the least traumatic method of fat processing. The main disadvantage is that this increases processing time and risks prolonged exposure of fat cells to the air, which in turn may lead to desiccation. Handling of the fat is also increased, so it may risk further damage. Cotton-gauze rolling is an alternative low trauma method of fat processing, again not part of the Coleman technique. A potential benefit is that the stromal component is largely retained.
When performing fat grafting, it is important to place fat in a cross-hatched pattern using long radial passes from multiple directions. This helps avoid placing an excess of fat in a single place or line. Injection in the face with the Coleman technique involves placement of small aliquots of fat in different tissue layers using 1-cc syringes and a 17-gauge blunt-tipped cannula 7–9 cm long. These are used to minimize trauma to the fat grafts and provide for accurate placement of small fat units; 10-cc syringes are used for harvest only. Fat should be placed on withdrawal, not advancement of the cannula. The pickle fork cannula is used only in areas of scarring and fibrosis where it is useful to break down the tissues and create a space for the fat grafts to sit. External digital manipulation is used to flatten clumps and minor irregularities during fat injection.1–3
The Brava system is an external tissue expander that has shown promising results when combined with fat transfer for primary breast augmentation. The expander is worn for 4 weeks before fat injection and for 1 week after. Graft survival can be substantially higher when external tissue expansion is used (82% compared to 55%).1,2 When performing primary breast augmentation with fat grafting, it is generally recommended that fat is injected into three planes: subcutaneously, prepectorally, and intramuscularly. Fat survival is improved when injected into muscle as it has a robust blood supply. However, there have been concerns raised about intramuscular injection of fat in view of the complications of buttock enhancement with fat transfer; so, care should be taken when injecting intramuscularly at any site of the body. Some surgeons will also inject directly into the breast parenchyma, although this does risk leaving small deposits of fat, which can necrose and potentially impact upon imaging for breast cancer further down the line. Long-term fat retention is improved when larger fat volumes are injected at each stage. In this patient with a BMI of 30, she should have a good volume of fat available for transfer (e.g., 300 cc per side), which could give her a meaningful autoaugment. While fat transfer has become very popular, it has not replaced the need for prosthetic breast augmentation, which still remains much more commonly performed. Many patients who wish to have breast augmentation are very slim and have little fat for transfer. Furthermore, because fat transfer often requires multiple stages, the financial implications tend to make it less cost-effective for patients who are self-funding. Harvesting additional fat and freezing this for future injections has theoretical appeal in that a ready supply of fat for injection in the office setting could provide further enhancement to the breast without the need for additional liposuction. Unfortunately, tissue viability drops with cryopreservation as most cryopreservative agents are also cytotoxic. The adipose-derived stem cell yield is significantly less in cryopreserved fat than from fresh fat; so overall, cryopreservation of fat is not a component of routine clinical practice and would not be indicated in this case.3,4
Massage of the recipient area following fat transfer should be avoided for at least 1 week following surgery, as this risks displacement of the grafts. Compression garments should be worn for a few weeks after surgery at both donor and recipient sites. Edema and bruising may be reduced by application of cool packs. Normal activities of daily living can be resumed early in the postoperative phase and full activities can be resumed after a few weeks. Anticoagulant medication can often be continued throughout the perioperative period or restarted the day after surgery, depending on the indication and medication type.1,2
Gluteal fat grafting has become a commonly practiced procedure across the globe and initially fat was purposely injected into both subcutaneous fat and the underlying musculature. The rationale for intramuscular injection was that graft take was enhanced secondarily to the higher vascularity of muscle. Indeed, this practice still continues in breast surgery where it is considered both safe and effective to inject into either transferred or native muscle, be it the rectus abdominis, LD, or the pectoralis major. In contrast there have been an alarming number of fatalities following gluteal fat grafting for buttock enhancement. These have been in fit, young patients who have succumbed to large fat emboli entering the pulmonary vasculature. The mechanism is thought to be due to direct injection of fat into large vessels within the gluteal muscles that have travelled back to the heart. Subsequent investigations into these deaths and multisociety task force safety meetings have been undertaken.1 The recommendations are that fat injections to the buttock must AT ALL TIMES BE SUBCUTANEOUS ONLY. The operators must stay as far away from the gluteal veins and sciatic nerve as possible and ensure they have clear awareness and control of the cannula tip placement throughout the entire procedure to ensure no inadvertent deeper passes are made. Access incisions that facilitate a superficial trajectory for each part of the buttock must also be used. Bendable cannula must not be used, and injection should be performed only when the cannula is moving to avoid high-pressure bolus injections. The risk of death must accordingly be discussed with each patient and the risks of this surgery must be weighed up against the potential benefits. Injection within the muscle remains an accepted technique in the breast, both in reconstruction and primary autoaugmentation settings. SIEF2 is a procedure used to allow women to remove their breast implants without losing all of the implanted volume. Fat is injected subcutaneously prior to implant removal and then further fat is injected into the soft tissues once the implants are removed. In primary breast augmentation using a fat transfer technique, fat is injected subcutaneously, prepectorally, and intramuscularly. Following free tissue transfer, fat injection into either fat or muscle is beneficial for contour and volume irregularities. Care, of course, should be taken to avoid the vascular pedicle and implant if there is once in situ.
Fat necrosis is a risk that can occur with breast surgery in general, for example, with reductions, reconstructions, and mastopexy. It is obviously a specific risk of fat transfer where grafts fail to obtain adequate new blood supply and scar tissue is formed. In some cases, it will not significantly affect the outcomes in terms of volume changes, but can leave firm or lumpy areas to the breasts which patients may find distressing. Fat necrosis must always be part of any discussion on breast or major reconstructive plastic surgery with patients during the consenting phase. The swelling following lipomodeling typically lasts for up to 6 months. At 3 months, the final outcome is unlikely to be apparent and again patients should be advised of this preoperatively. Mammography should not be compromised with an experienced radiologist, providing they understand the treatment she has had. Also given her age, mammography should have been performed preoperatively and is unlikely to be required at this stage.1 Fat transfers are affected by weight changes and behave as they would have at the donor site. Therefore, as this patient has lost weight, the transferred fat will also be affected, and it is unlikely that three quarters of the transferred volume will remain. This again is one of the key areas that must be discussed with patients preoperatively.