Fat grafting survival rate explained thoroughly! From absorption mechanisms to the latest technologies for increasing survival rates
Autologous fat injection (fat grafting) for facial contouring and rejuvenation is a highly popular treatment in aesthetic medicine due to its high safety profile and natural-looking results. However, the greatest challenge for both patients and physicians is determining "how much of the injected fat will survive (survival rate)." Since 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 based on meta-analysis, key points for maximizing survival rates, and the latest nanofat technology. Additionally, we introduce characteristics of individuals who tend to have lower survival rates and how to develop an intelligent treatment plan based on this information.
1. Absorption mechanism: Why does injected fat decrease?
Behind the volume reduction following fat injection lies the harsh environment in which transplanted adipocytes are placed and the associated mechanism of necrosis. For transplanted fat to survive, a steady supply of nutrients and oxygen from surrounding tissue is essential.
In the early stages of fat grafting, the transplanted adipose tissue has not yet established a dedicated vascular network (blood supply). Therefore, during the first 24 to 48 hours after transplantation, nutrients and oxygen are obtained only through osmosis from surrounding tissue fluid or direct diffusion (Wei 2017). Related to this fact, Carpaneda and colleagues, who conducted important research on fat graft survival, discovered that the survival rate of transplanted fat depends strongly on "the thickness and geometric shape of the fat mass."
According to the concept of "borderland" they proposed, approximately 40% of tissue in a boundary zone 1.5 ± 0.5 mm from the periphery of a transplanted fat mass can survive. Conversely, when large fat masses exceeding 3 mm in diameter are injected, the central portion of the fat mass cannot be reached by diffusion from surrounding tissue fluid, causing plasma absorption impairment. As a result, the adipose tissue in the center falls into sustained ischemia and hypoxia, ultimately undergoing necrosis and liquefaction (Chou 2017) (Wei 2017). Therefore, the larger the fat mass being injected, the lower the survival rate becomes, inversely proportional to its diameter.
Furthermore, the initial mechanism of volume reduction after transplantation includes the absorption of tumescent fluid (sham fluid) injected together with fat and non-viable cells that have already lost viability. Additionally, even after initial volume reduction stabilizes, gradual volume reduction may be observed over 12 months post-transplantation. This may be attributed to surviving mature adipocytes releasing lipids (delipidization) as they adapt to environmental changes, and differentiating into lipid-free fibroblast-like cells (Lv 2020).
2. Actual survival rates shown by meta-analysis (Lv 2020: average 47%)
Fat grafting survival rates have historically been assessed based on physician subjective judgment and experience. However, recent studies employ 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 (a total of 1011 patients) (Lv 2020).
According to this meta-analysis, fat grafting survival rates to the face varied from 26% to 83% across studies, but integrated data from 21 eligible studies revealed that the average survival rate at the most recent follow-up timepoint was 47% (95% confidence interval: 41%–53%) (Lv 2020). In other words, it is reasonable to consider that approximately half of the injected fat ultimately survives.
Furthermore, subgroup analysis by follow-up period clarified the timeline of when fat diminishes. The survival rate gradually decreased over time: 53% at 3 months post-operation, 49% at 6 months, and 41% at 12 months. From this data, we can see 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 have been shown to arise depending on the volume measurement method. In 15 studies using 3D scanning for volume measurement, the average survival rate was 43%, whereas in 5 studies using CT, the average survival rate was calculated as 57%, which is higher. This suggests that CT-based evaluation may somewhat overestimate the survival rate (Lv 2020).
3. Five key points for increasing survival rate
To minimize the proportion of fat being absorbed and maximize the survival rate, ingenuity is required in surgical technique and fat processing methods. We introduce five important points for improving survival rates derived from past clinical research.
- Fine fat injection (microfat grafting)As described in the absorption mechanism mentioned above, when fat globules are large, the central portion undergoes necrosis. To prevent this, the concept of "Micro-Autologous Fat Transfer (MAFT)" proposed by Lin et al. in 2006 recommends that the volume of each compartment (lump) of fat being injected should be less than 1/100 mL (0.01 mL). By keeping the radius of fat globules at approximately 1.3 mm or less, nutrient diffusion from tissue fluid more easily reaches the central portion, making it possible to avoid complications such as necrosis and cyst formation. Using a specialized injector (such as MAFT-GUN), the technique of precisely injecting an extremely minute amount of fat of 1/120 mL (0.0083 mL) per trigger is effective (Chou 2017).
- Dispersed injection into multiple layers and multiple pathways (Multiplane · Multichannel)Rather than injecting fat all in one location, dispersing the injection into multiple layers (multiplane) or multiple pathways (multichannel) is an extremely effective method for increasing the contact area between the transplanted fat and the surrounding vascular bed (Lv 2020). For example, in the case of forehead contour formation, by transplanting fat finely scattered across three different depths—the deep layer directly above the periosteum, the intramuscular layer of the frontalis muscle (intermediate layer), and the subcutaneous tissue layer below the dermis (superficial layer)—blood supply to the transplanted fat is optimized (Chou 2017).
- Appropriate fat processing through centrifugation or filtrationThe process of removing impurities such as blood, oil, and tumescent fluid from the suctioned fat is also important. According to meta-analysis data, when "centrifugation method" or "filtration method" are used as fat processing techniques, a tendency toward more consistently stable survival rates is confirmed compared to the "sedimentation method" where separation occurs simply by letting it stand. In 16 studies using centrifugation, the survival rate was 47%, and in 4 studies using filtration, the survival rate was 36% with less variation between studies, whereas the sedimentation method showed a survival rate of 46% but with very high heterogeneity between studies, demonstrating unstable results (Lv 2020).
- Secondary and subsequent additional injections (Touch-up)It is known that fat injection results in a dramatic improvement in survival rate when performed multiple times. In the meta-analysis comparison, whereas the average survival rate in the first injection was 45% (4 studies), the average survival rate in the second injection reached 63% (4 studies). The reason for this is thought to be that the first fat transplantation increases the thickness of soft tissue at the recipient site (transplant destination), and a foundation rich in blood flow is formed, creating an environment where second-round fat 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 garnering attention. In the meta-analysis studies reviewed, when SVF or PRP were used as adjunctive factors, an unusual phenomenon was reported: after experiencing initial volume reduction by 3 months post-procedure, average volume gradually increased and recovered between 3 and 12 months. These adjunctive factors are thought to powerfully promote angiogenesis, not only improving the ischemic state but also supporting fat survival and volume recovery by promoting stem cell proliferation and differentiation into adipocytes (Lv 2020).
4. Nanofat stem cells and their potent effects (Wei 2017)
In recent years, a revolutionary technique in skin rejuvenation and improvement of fat graft survival rate is "nanofat" technology. 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 are reported in detail (Wei 2017).
The stromal vascular fraction (SVF) obtained through liposuction is rich in diverse cell types including adipose-derived stem cells (ASCs), mature adipocytes, vascular endothelial cells, fibroblasts, and pericytes. These are known to promote rapid angiogenesis at the transplant site and increase survival rate. In Wei et al.'s technique, harvested fat particles are mechanically emulsified by continuous extrusion between syringes for 3 minutes, converting them into a liquid state. Subsequently, passage through an ultra-fine filter generates extremely small "nanofat" with a diameter of approximately 50–100 μm. Interestingly, cells isolated and cultured from this nanofat without collagenase digestion (nanofat-derived stem cells: NFSCs) possess morphology and function similar to mesenchymal stem cells and maintain the ability to differentiate into adipocytes, osteoblasts, and chondrocytes (Wei 2017).
Because nanofat is far smaller in size than conventional fat particles, it dramatically increases the contact surface area between the concurrently injected large structural fat particles and SVF. This maximizes the beneficial paracrine effects (action that affects surrounding cells) of SVF in fat transplantation (Wei 2017).
Additionally, Wei et al. investigated the synergistic effects of platelet-rich fibrin (PRF) made from the patient's own blood. PRF contains abundant growth factors that promote tissue repair and regeneration, such as 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 potently 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 serving as 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, newly isolated nanofat rich in SVF, PRF, and autologous structural fat were mixed and transplanted to 62 patients (test group) presenting with facial soft tissue depression and severe signs of aging. This was compared to a control group of 77 patients who received conventional autologous fat transplantation alone. As a result, the group receiving nanofat + PRF combination transplantation not only showed marked improvement in facial depression symptoms, but also demonstrated dramatic improvement in skin texture, elasticity, pore size, and hydration levels as assessed objectively using devices such as VISIA and SOFTA5.5 compared to pre-procedure, with a trend of improvement also observed in wrinkles and age spots. This is thought to be due to the paracrine effects of SVF contained in nanofat and the anti-aging effects of cytokines 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 far exceeded 90%, demonstrating overwhelmingly superior results compared to the control group whose satisfaction rate was below 70%. Furthermore, among the 62 patients in the test group, only 9 patients (14.5%) required a second injection, with the majority achieving satisfactory results with a single injection. No severe complications such as fat nodules (induration), liquefaction, or cyst formation were observed, demonstrating that the technique combining nanofat and PRF is an exceptionally safe and long-lasting excellent therapeutic method (Wei 2017).
5. Characteristics of people with low retention rates
Research has shown that fat grafting retention rates vary among individuals and are influenced by patients' age and the purpose of treatment.
Elderly patientsAge can be a negative factor in fat retention rates. According to research by Gerth and Denadai, the volume retention rate in elderly patient groups is significantly lower compared to younger age groups. This is thought to be related to the fact that as we age, the proliferation dynamics of adipose-derived stem cells (ASCs) within fatty tissue deteriorate and their differentiation capacity declines (Lv 2020). Aged stem cells have weakened 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 seeking volume enhancement (augmentation) for cosmetic purposesIn a meta-analysis subgroup analysis comparing retention rates by treatment "indication (purpose)," the average retention rate for patients who underwent fat grafting for cosmetic augmentation was 42% (8 studies). In contrast, patients who underwent fat grafting as reconstructive treatment for congenital deformities such as hemifacial atrophy (Romberg disease) had an average retention rate of 51% (8 studies), demonstrating a tendency for better retention rates in patients with congenital deformities. While there is debate about the reason, it is speculated that the soft tissue in patients with congenital deformities forms a "loose scaffold" that provides abundant nutrition and space for the 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 is hindered, and retention rates may be slightly reduced.
6. Smart treatment planning: An approach based on retention rates
As evidence has made clear, injected fat does not achieve 100% retention. Based on the "average 47%" retention rate shown in meta-analyses and the fact that volume decreases significantly in the first 3 months post-operatively (Lv 2020), physicians and patients need to establish realistic and strategic treatment plans.
Implementation of overcorrectionAnticipating the limits of retention rates, "overcorrection"—intentionally injecting more fat than the desired final volume—is commonly performed during surgery. For example, in Wei's research protocol, calculations accounting for absorption, and 25% to 30% more fat than the target final volume is injected (Wei 2017). This is designed so that after several months when fat is absorbed, the ideal volume remains. However, excessive injection increases tissue pressure and can cause necrosis and fibrosis from blood flow obstruction, so it is important to understand that there are limits to the amount that can be injected at one time.
Planning based on "two or more treatments"Rather than attempting to achieve perfect volume in a single surgery, planning based on "multiple treatments" from the start is a wise choice that ultimately increases patient satisfaction. As previously mentioned, meta-analysis has proven that second fat grafting has a significantly higher retention rate (63%) compared to first grafting (45%) (Lv 2020). The transplanted fat from the first procedure builds a vascular network and expands skin and tissue to create a foundation, making the second fat grafting dramatically 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 desiring further volume or fine-tuning is considered 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% patient satisfaction with results (Chou 2017).
Rigorous safe and reliable injection techniqueDelicate physician technique is essential to prevent complications while improving retention rates. To prevent embolic events from erroneous intra-vascular injection (such as blindness or stroke), aspiration—pulling the syringe plunger before injection and confirming that no blood is present—is necessary. Additionally, injection must be performed at the lowest possible pressure and slowly. To prevent fat from accumulating in one location and blocking blood flow, injecting in a fan pattern while moving the needle, and creating fine lines across multiple planes (multiplane-multichannel injection) is the key to achieving safe and high retention rates (Wei 2017).
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7. Summary
Fat injection (fat grafting) is a wonderful treatment that uses one's own tissue, eliminating the risk of foreign body reactions and enabling natural facial rejuvenation and contouring over the long term. However, as objective meta-analysis data demonstrates, the average engraftment rate of injected fat is approximately 47%, with roughly half being absorbed due to volume reduction centered around 3 months post-procedure (Lv 2020).
The primary cause of fat absorption is necrosis due to 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 in dispersed layers across multiple tissue planes is essential (Chou 2017). Additionally, appropriate processing such as centrifugation contributes to stable engraftment rates (Lv 2020).
In recent years, cutting-edge techniques have emerged that combine ultrafine "nanofat" obtained through mechanical emulsification with blood-derived "PRF (platelet-rich fibrin)". This method, by combining the power of nanofat-derived stem cells (NFSCs) with PRF's growth factors that promote angiogenesis and fat differentiation, has been proven to deliver not merely volume augmentation but also dramatic skin quality improvement (rejuvenation) and exceptionally high patient satisfaction rates (90% or higher) (Wei 2017).
On the other hand, it is important to understand that in elderly patients or those desiring cosmetic volume enhancement, engraftment rates tend to be somewhat lower due to diminished stem cell function and limited tissue accommodation (Lv 2020).
The wisest approach to achieving successful fat injection is to formulate a "treatment plan that anticipates fat absorption." By performing 25–30% overcorrection (overcorrection), establishing the foundation with the first procedure, and completing the result with a second injection (engraftment rate: 63%) for touch-up (Lv 2020), you can safely and reliably achieve your 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 research presentations at domestic and international academic conferences, he is involved in technical guidance and education across Zetith Beauty Clinic. He specializes in precision aesthetic medicine based on anatomical evidence and pursues natural results tailored to each individual's skeletal structure and tissues.