Complete explanation of fat graft survival rate! From absorption mechanisms to the latest technologies for improving survival rates
Autologous fat injection (fat grafting) for facial contouring and rejuvenation is a highly popular treatment in aesthetic medicine because of its high safety profile and natural-looking results. However, the biggest challenge for both patients and physicians is "how much of the injected fat will survive (survival rate)." Because some of the fat is absorbed by the body, results are difficult to predict. This article provides a detailed explanation—based on scientific and medical evidence—of the absorption mechanisms in fat grafting, accurate survival rates determined by meta-analysis, key points for maximizing survival rate, and the latest nanofat technology. We also introduce the characteristics of people who tend to have lower survival rates and how to develop a smart treatment plan taking these factors into account.
1. Absorption mechanism: Why does injected fat decrease?
Behind the volume reduction that occurs after fat injection lies the harsh environment in which transplanted adipocytes are placed and the accompanying mechanism of necrosis. For transplanted fat to survive, a supply of nutrients and oxygen from surrounding tissues is essential.
In the early stages of fat grafting, the transplanted fatty tissue does not yet have an established dedicated vascular network (blood supply). Therefore, for the first 24 to 48 hours after transplantation, nutrients and oxygen are obtained only through infiltration from surrounding tissue fluid or direct diffusion (Wei 2017). In connection with this fact, Carpaneda and colleagues, who conducted important research on fat graft survival, discovered that the survival rate of transplanted fat is strongly dependent on "the thickness and geometric shape of the fat mass."
According to the "borderland" concept they proposed, approximately 40% of tissue in the boundary region 1.5 ± 0.5 mm from the periphery of the transplanted fat mass can survive. Conversely, if a large fat mass exceeding 3 mm in diameter is injected, the center of the fat mass cannot be reached by diffusion from surrounding tissue fluid, causing absorption impairment of the plasma. As a result, the fatty tissue at the center undergoes sustained ischemia and hypoxia, ultimately leading to necrosis and liquefaction (Chou 2017) (Wei 2017). Therefore, the larger the fat mass being injected, the more the survival rate decreases in inverse proportion to its diameter.
Furthermore, as an initial mechanism of volume reduction after transplantation, the tumescent fluid (sham fluid) injected along with the fat, and non-viable cells that have already lost viability, are absorbed by the body. Additionally, even after initial volume reduction stabilizes, gradual volume reduction may be observed over the 12 months following transplantation. This may be due to the fact that surviving mature adipocytes release lipids (delipidization) as they adapt to environmental changes and differentiate into fibroblast-like cells devoid of lipids (Lv 2020).
2. Actual survival rates shown by meta-analysis (Lv 2020: average 47%)
Fat graft survival rates have previously been assessed largely based on physicians' subjective impressions and experience. However, recent research has employed objective volume measurement using MRI, CT, and 3D scanning. The systematic review and meta-analysis published by Lv and colleagues in 2020 provides highly reliable data integrating 27 studies using objective measurement methods (totaling 1,011 patients) (Lv 2020).
According to this meta-analysis, the fat graft survival rate for facial injection varied from 26% to 83% across studies, but the integrated data from 21 eligible studies showed that the average survival rate at the latest follow-up was 47% (95% confidence interval: 41%–53%) (Lv 2020). In other words, it is reasonable to assume that slightly less than half of the injected fat ultimately becomes established.
Additionally, subgroup analysis by follow-up period has clarified the timeline of when fat decreases. The survival rate gradually declined over time, reaching 53% at 3 months post-procedure, 49% at 6 months, and 41% at 12 months. This data shows that the greatest volume reduction of transplanted fat occurs within the first 3 months after surgery (Lv 2020).
Interestingly, significant differences in reported survival rates were also observed depending on the volume measurement method. In 15 studies measuring volume using 3D scanning, the average survival rate was 43%, whereas in 5 studies using CT, the average survival rate was calculated higher at 57%. This suggests that CT-based assessment may somewhat overestimate the survival rate (Lv 2020).
3. 5 key points for improving survival rate
To minimize the proportion of fat that is absorbed and maximize survival rate, ingenuity is required in surgical technique and fat processing methods. We present 5 important key points for improving survival rate derived from past clinical research.
- Fine fat injection (Microfat grafting)As described in the absorption mechanism mentioned above, when a fat graft is large, the center undergoes necrosis. To prevent this, the concept of "Micro Autologous Fat Transplantation (MAFT)," proposed by Lin et al. in 2006, recommends that the volume of a single compartment (lump) of injected fat should be less than 1/100 mL (0.01 mL). By maintaining the radius of the fat graft at approximately 1.3 mm or less, nutrient diffusion from tissue fluid more readily reaches the center, allowing avoidance of complications such as necrosis and cyst formation. Using dedicated injectors (such as MAFT-GUN), a highly precise injection technique that delivers extremely minute amounts of fat—1/120 mL (0.0083 mL) per trigger—is effective (Chou 2017).
- Multi-layer, multi-channel dispersed injection (Multiplane, Multichannel)Rather than injecting fat all at one location, distributing the injection across multiple layers (multiplane) and multiple entry routes (multichannel) is a highly effective method for increasing the contact surface area between the transplanted fat and the surrounding vascular bed (Lv 2020). For example, in contouring the forehead, by finely distributing the fat across three different depths—the deep layer directly above the periosteum, the intermediate muscle layer within the frontalis muscle, and the shallow subcutaneous tissue layer beneath the dermis—the blood supply to the transplanted fat is optimized (Chou 2017).
- Appropriate fat processing via centrifugation or filtrationThe process of removing impurities such as blood, oil, and tumescent fluid from the aspirated fat is also important. According to meta-analytic data, when "centrifugation" or "filtration" techniques are used as fat processing methods, a more consistently stable graft take rate tends to be obtained compared to the "sedimentation" method, which simply relies on static separation. In 16 studies using centrifugation, the graft take rate was 47%, and in 4 studies using filtration, it was 36%, with little variation between studies; in contrast, the sedimentation method showed a graft take rate of 46% but with very high heterogeneity between studies, indicating unstable results (Lv 2020).
- Subsequent injection (touch-up) on second and later occasionsIt is known that performing fat injection multiple times results in a dramatic improvement in the graft take rate. In meta-analytic comparison, while the average graft take rate on first injection was 45% (4 studies), the average graft take rate on second injection reached 63% (4 studies). The reason for this is thought to be that the first fat transplantation increases the thickness of the soft tissue at the recipient site (transplant area), forming a blood-rich foundation, thereby creating an environment in which the second fat graft is more likely to survive (Lv 2020).
- Combination use of cells and growth factors such as SVF and PRPLiposuctionTechniques that mix stromal vascular fraction (SVF) contained in adipose tissue or platelet-rich plasma (PRP) extracted from the patient's own blood with fat for transplantation are also gaining attention. In studies included in the meta-analysis, when SVF or PRP were used as adjunctive factors, after experiencing initial volume reduction up to 3 months post-procedure, a unique phenomenon was reported in which average volume gradually increased and recovered between 3 and 12 months. These adjunctive factors are thought to support fat survival and volume recovery by strongly promoting angiogenesis, improving ischemic conditions, and promoting stem cell proliferation and differentiation into adipocytes (Lv 2020).
4. Nanofat stem cells and their powerful effects (Wei 2017)
In recent years, the "nanofat" technique has been bringing revolutionary effects in skin rejuvenation and improving fat graft survival rates. In the research by Wei et al., the excellent clinical effects of autologous structural fat transplantation using nanofat and the biological mechanisms underlying these effects have been reported in detail (Wei 2017).
The stromal vascular fraction (SVF) obtained by liposuction is rich in diverse cells including adipose-derived stem cells (ASCs), mature adipocytes, vascular endothelial cells, fibroblasts, and pericytes, and it is known that these promote rapid angiogenesis at the transplant site and increase survival rate. In the technique by Wei et al., harvested fat particles are mechanically emulsified between syringes by continuously pushing them together for 3 minutes, changing them into a liquid state. Subsequently, by passing through an ultra-fine filter, extremely small "nanofat" particles with a diameter of approximately 50–100 μm are generated. Interestingly, cells separated and cultured from this nanofat without collagenase digestion (nanofat-derived stem cells: NFSCs) have been confirmed to possess the same morphology and function as mesenchymal stem cells, and maintain the ability to differentiate into adipocytes, osteoblasts, and chondrocytes (Wei 2017).
Because nanofat is much smaller in size than conventional fat particles, it dramatically increases the contact surface area between simultaneously injected large structural fat particles and SVF. This maximizes the beneficial paracrine effects of SVF in fat transplantation—the capacity to influence surrounding cells (Wei 2017).
Furthermore, Wei et al. investigated the combined effects of platelet-rich fibrin (PRF) created from the patient's own blood. PRF contains large amounts of growth factors that promote tissue repair and regeneration, including vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), transforming growth factor (TGF-β), and epidermal growth factor (EGF). In laboratory co-culture, PRF powerfully promoted the growth and proliferation of NFSCs in a dose- and time-dependent manner. Additionally, after 14 days of culture, mRNA expression levels of genes that are markers of adipogenesis (PPARγ2, C/EBPα, ADD1) were significantly elevated compared to the control group, demonstrating that PRF promotes adipogenic differentiation of stem cells (Wei 2017).
In the clinical trial applying this basic research, 62 patients (test group) with facial soft tissue depression and severe signs of aging received transplantation of a mixture of newly isolated nanofat rich in SVF, PRF, and autologous structural fat. This was compared with a control group of 77 patients who received conventional autologous fat transplantation only. As a result, the group that received nanofat + PRF mixture transplantation not only showed marked improvement in facial depression symptoms, but also demonstrated dramatic improvements in skin texture, elasticity, pore size, and hydration when evaluated objectively using devices such as VISIA and SOFT5.5 compared to pre-procedure measurements. Additionally, improvements in wrinkles and pigmentation spots were also observed. This is thought to be due to the paracrine effects of SVF contained in nanofat and the anti-aging effects of cell factors contained in PRF (Wei 2017).
In long-term follow-up at 12 and 24 months post-procedure, the average satisfaction rate of patients in the nanofat group significantly exceeded 90%, showing overwhelmingly higher results compared to the control group, which had a satisfaction rate of less than 70%. Furthermore, among the 62 patients in the test group, only 9 patients (14.5%) required a second injection, with the majority of patients achieving satisfactory results with a single injection. No serious complications such as fat hardening (induration), liquefaction, or cyst formation were observed, demonstrating that the technique combining nanofat and PRF is an exceptionally safe and long-lasting excellent treatment method (Wei 2017).
5. Characteristics of people with low graft survival rates
Research has shown that fat graft survival rates vary among individuals and are influenced by patient age and the purpose of treatment.
Older patientsAge can be a negative factor in fat graft survival rates. According to research by Gerth and Denadai, the volume survival rate in older patient groups was significantly lower compared to younger patient groups. This is thought to be related to the fact that with aging, the proliferation dynamics of adipose-derived stem cells (ASCs) within adipose tissue deteriorate, and their differentiation capacity also declines (Lv 2020). Aged stem cells lose their ability to overcome the harsh ischemic environment after transplantation, construct new blood vessels, and generate new fat cells, resulting in a higher absorption rate.
Patients desiring volume augmentation (filling) for cosmetic purposesIn subgroup analysis of a meta-analysis, when graft survival rates were compared by treatment "indication (purpose)," the average survival rate for patients who underwent fat injection for cosmetic augmentation was 42% (8 studies). In contrast, the average survival rate for patients who underwent fat injection as reconstructive treatment for congenital deformities such as hemifacial atrophy (Romberg disease) was 51% (8 studies), showing a trend of better survival rates in congenital deformity patients. While there is debate about the reason, it is speculated that the soft tissue of congenital deformity patients forms a "loose scaffold" that provides abundant nutrients and space for transplanted fat cells, creating an environment where fat is more likely to survive (Lv 2020). Conversely, when attempting to forcibly add volume to healthy tissue for cosmetic purposes, tissue pressure tends to increase, blood flow may be impeded, and graft survival rates may be slightly reduced.
6. Smart treatment planning: An approach based on graft survival rates
As the evidence clearly shows, transplanted fat does not achieve 100% survival. Based on the "average 47%" survival rate shown by meta-analysis and the fact that volume decreases significantly during the first 3 months after surgery (Lv 2020), physicians and patients must develop realistic and strategic treatment plans.
Implementation of overcorrectionAnticipating the limitations of survival rates, "overcorrection" — intentionally injecting more fat than the desired final volume — is commonly performed during surgery. For example, in the research protocol by Wei et al., 25% to 30% more fat than the target final volume is injected, accounting for the amount that will be absorbed (Wei 2017). This is designed so that the ideal volume remains after the fat is absorbed over several months. However, it is important to understand that excessive injection increases tissue pressure and can cause necrosis and scar tissue due to blood flow impairment, so there are limits to the amount that can be injected at one time.
Planning for "two or more treatments"Rather than attempting to achieve perfect volume in a single surgery, establishing a plan that assumes "multiple treatments" from the start is a wise choice for achieving greater overall satisfaction. As mentioned earlier, meta-analysis has proven that the second fat injection has a significantly higher survival rate (63%) compared to the first injection (45%) (Lv 2020). Because the first transplanted fat constructs a vascular network and expands the skin and tissue to create a foundation, the second fat injection is overwhelmingly more likely to survive. In clinical research by Chou et al., implementing a "second touch-up session" 4 to 6 months after the first MAFT (micro autologous fat transfer) for patients seeking additional volume or fine-tuning was found to be effective. In this study, patient satisfaction after receiving two MAFTs including touch-up was remarkable, with 86.4% answering "very satisfied" and 13.6% "satisfied," for a total of 100% of patients satisfied with the results (Chou 2017).
Rigorous safe and precise injection techniqueTo prevent complications while improving graft survival rates, refined technique by the physician is essential. To prevent embolic events (blindness, cerebral infarction, etc.) from misinjection into blood vessels, it is necessary to always pull the syringe plunger before injection and confirm that no blood has been mixed in (aspiration). Additionally, injection must be performed at the lowest possible pressure and slowly. To prevent fat from clumping in one area and blocking blood flow, injecting in a fan-like motion while moving the needle and injecting finely in multiple planes and channels (multi-plane, multi-channel injection) is the key to achieving safe results with high survival rates (Wei 2017).
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7. Summary
Fat injection (fat grafting) is a wonderful treatment that uses one's own tissues, eliminating the risk of foreign body reactions and achieving natural rejuvenation and facial contouring over the long term. However, as objective meta-analysis data demonstrate, the average engraftment rate of injected fat is approximately 47%, with roughly half being absorbed as volume decreases during the 3 months post-procedure (Lv 2020).
The primary cause of fat absorption is necrosis from central ischemia and hypoxia (Wei 2017). To prevent this, the technique of injecting ultra-small fat particles (microfat) with a radius of 1.3 mm or less, dispersed across multiple tissue planes, is essential (Chou 2017). Additionally, appropriate processing such as centrifugation contributes to stable engraftment rates (Lv 2020).
Recently, cutting-edge technology combining ultrafine "nanofat" obtained through mechanical emulsification with "PRF (platelet-rich fibrin)" derived from blood has emerged. This approach harnesses the power of nanofat-derived stem cells (NFSCs) combined with PRF's growth factors to promote angiogenesis and adipogenic differentiation, delivering not merely volume enhancement but also significant skin quality improvement (rejuvenation) and exceptionally high patient satisfaction rates (90% or higher), as demonstrated in the literature (Wei 2017).
On the other hand, it is important to understand that elderly patients and those seeking volume enhancement for cosmetic purposes may experience slightly lower engraftment rates due to declining stem cell function and limited tissue accommodation (Lv 2020).
The smartest approach to achieving successful fat grafting is to develop a "treatment plan that anticipates fat absorption." By performing 25–30% overcorrection (overcorrection) (Wei 2017), establishing the foundation in the first procedure, and completing the result with a second injection (touchup) at 63% engraftment rate (Lv 2020) (Lv 2020), you can safely and reliably achieve the ideal facial contour and youthful skin (Chou 2017).
References
- Lv Q, Li Y, Fan Y, et al. Fat Grafting for Facial Rejuvenation: A Systematic Review and Meta-analysis of Volume Retention. Aesthetic Plastic Surgery. 2020DOI
- Egro F, Roy E, Rubin J, et al. Evolution of the Coleman Technique. Plastic & Reconstructive Surgery. 2022DOI
- Firriolo J, Condé-Green A, Pu L. Fat Grafting as Regenerative Surgery: A Current Review. Plastic & Reconstructive Surgery. 2022DOI
- Wei H, Gu S, Liang Y, et al. Nanofat-Derived Stem Cells with Platelet-Rich Fibrin for Facial Rejuvenation. Oncotarget. 2017DOI
Author of this article
Hiromitsu NakamuraPhysician
Zetith Beauty Clinic Ginza, Osaka, Fukuoka
With a track record of presenting research at domestic and international academic conferences, he is involved in technical guidance and education across the Zetith Beauty Clinic. He specializes in precise aesthetic medicine based on anatomical evidence and pursues natural results tailored to each individual's skeletal structure and tissues.