Basic Knowledge About Facial Fat Injection (Autologous Fat Grafting)
Facial fat injection (autologous fat grafting) is widely practiced in aesthetic medicine and reconstructive surgery for the purpose of restoring lost volume, contouring, and skin tissue regeneration (rejuvenation). This article provides detailed explanations based on provided medical literature regarding the basic mechanisms of fat injection, the evolution toward the latest nanofat technology, anatomical injection compartments, the latest scientific data on graft survival rates, differences from fillers such as hyaluronic acid, and serious risks and complications.
1. How Fat Injection Works
Autologous fat is considered an ideal filler material because its supply source is abundant, it has high biocompatibility, and carries low risk of allergy or rejection reactions (Lv 2020). However, the mechanism by which transplanted fat survives long-term (engrafts) is extremely complex.
Immediately after injection, transplanted fat tissue lacks a reliable blood supply network and obtains nutrients solely through osmotic infiltration from surrounding tissue fluid. If a dedicated blood supply is not rapidly established, fatty tissue in the center of the graft may undergo sustained ischemia and hypoxia, potentially resulting in necrosis and liquefaction. According to the "borderland concept" proposed by Carpaneda and colleagues, only 40% (Wei 2017) of tissue within a 1.5±0.5 mm range from the periphery of a transplanted fat mass survives.
The key to solving this engraftment challenge isfat liposuctionthe stromal vascular fraction (SVF) obtained from aspirates. SVF contains not only mature adipocytes but also diverse cells such as adipose-derived stem cells (ASCs), vascular endothelial cells, fibroblasts, and pericytes. These cells promote rapid angiogenesis of the graft and have been shown to dramatically improve graft survival rates. Furthermore, platelet-rich fibrin (PRF) generated by centrifugation from autologous blood, when used concurrently, results in sustained release of growth factors such as PDGF, VEGF, TGF-β1, TGF-β2, and EGF, powerfully promoting tissue repair and regeneration. Conventionally, 20% to 90% (Wei 2017) of injected fat is said to be reabsorbed in traditional fat grafting; however, the use of SVF and PRF prevents ischemia in the graft center and plays a very important role in long-term engraftment.
2. Evolution from Coleman Technique to Nanofat
The history of fat injection is long; since Neuber first reported fat grafting in 1893 (Lv 2020), numerous technical innovations have been made (Chou 2017).
Coleman Technique (Structural Fat Grafting)
Dr. Coleman made major contributions to standardizing fat injection. In 1998, he proposed "Structural fat grafting," which involves delicate fat harvesting, purification by centrifugation, and injection of fine fat parcels across multiple layers. Coleman argued that to prevent necrosis of the fat mass center, in thin-skinned areas such as the periocular region, the amount of each injected parcel should be 1/30 to 1/50 mL (0.020–0.033 mL) (Chou 2017).
Birth of MAFT (Micro-Autologous Fat Transplantation)
Subsequently, in 2006, MAFT (Micro-Autologous Fat Transplantation) was proposed by Dr. Lin and colleagues. The MAFT concept emphasized reducing injected fat parcels to less than 1/100 mL (0.01 mL)—a sphere size with a radius of 1.3 mm—to avoid complications (cyst formation, nodulation, calcification, etc.) and ensure engraftment throughout the fat mass center. Using dedicated precision injection devices such as MAFT-GUN made it possible to consistently transplant extremely small amounts of fat ranging from 1/120 mL (0.0083 mL) to 1/240 mL (Chou 2017) in a controlled manner.
Emergence of Nanofat
Further, in 2013, "nanofat" was reported by Tonnard and colleagues. This consists of microparticles obtained by mechanically emulsifying harvested fat between syringes and passing it through a dedicated filter. Nanofat particles are 100 μm (Wei 2017) or smaller in diameter (or 800 microns or less) and are rich in stem cells (ASCs) and SVF. Rather than providing physical volume, nanofat is used for skin rejuvenation (rejuvenation), fine line improvement, and regeneration of radiation-damaged tissue (Crowley 2021).
Currently, within the concept of Injectable Tissue Replacement and Regeneration (ITR2), fat is classified into three types (Crowley 2021) according to size and is used selectively depending on anatomical application:
- Millifat:2.4 mm or larger (Crowley 2021). Used for deep fat compartments and foundation formation over bone.
- Microfat:1.2 mm or larger (Crowley 2021). Used for superficial fat compartments and subcutaneous tissue.
- Nanofat (Nanofat): 800 microns or less (Crowley 2021). Injected into the subcutis or dermis (via microneedling, etc.) and used for skin quality improvement and tissue regeneration.
3. Anatomical Compartments and Indications
For safe and effective facial fat grafting, a deep understanding of anatomical compartments is essential. For example, the forehead (frontal region) is composed of the following 3 layers (Chou 2017), and appropriately sized fat is injected into each:
- Deep layer (on periosteum / beneath frontalis muscle): The space between the frontal bone and frontalis muscle. Milliliter-sized fat is used in this layer to build a foundation and create the basis of facial contours.
- Middle layer (within frontalis muscle): A layer within the frontalis muscle rich in blood flow, where microfat is injected to maintain volume.
- Superficial layer (subcutaneous tissue): The layer between the dermis and frontalis muscle, where minute fat is placed to smooth contours.
In Asian culture, forehead roundness and fullness (Frontal fullness) are thought to indicate popularity and leadership qualities, and the cosmetic need for forehead volume enhancement is very high (Chou 2017).
Indications for facial fat grafting are diverse, including age-related facial volume loss, asymmetry, congenital or acquired deformities, progressive hemifacial atrophy (Romberg disease), and post-traumatic depression (Lv 2020). By replenishing tissue of the same nature (fat) as the lost tissue in the anatomically appropriate layer, natural three-dimensional structural restoration becomes possible, rather than merely filling wrinkles.
4. Graft Survival Rate (Lv 2020)
The greatest challenge of facial fat grafting is the difficulty in predicting graft survival rate. A systematic review and meta-analysis by Lv et al. (Lv 2020) provides important objective and quantitative data on this survival rate.
This study analyzed 27 studies including 1011 patients who underwent facial fat grafting. The post-operative follow-up period was 3–24 months, and the survival rate by objective measurement showed a wide variation of 26%–83%. The mean survival rate across all studies was 47% (95% CI 41–53%) (Lv 2020).
The following data demonstrate factors affecting graft survival rate.
- Differences by measurement method: The survival rate was 43% using 3D scanning, 57% by CT, and 40% by high-resolution ultrasound (HRUS). A significant difference was found between 3D scanning and CT (p=0.01 (Lv 2020)), suggesting that CT tends to overestimate the survival rate.
- Fat processing method: The survival rate was 47% using centrifugation, 36% by filtration, and 46% by gravity sedimentation (Lv 2020). No clear statistical evidence was found that any one method was superior.
- Number of injections: Whereas the survival rate for initial injection was 45%, the survival rate for secondary injection was 63% (Lv 2020), confirming that performing multiple injections significantly improves graft survival.
- Indications:In patients with congenital deformities, the engraftment rate was 51%, and in cosmetic augmentation, it was 42% (Lv 2020).
Additionally, the complication rate in this meta-analysis was only 2.8% (Lv 2020), confirming that facial fat injection has high overall safety.
5. Differences from Fillers
As options for supplementing facial volume, synthetic fillers such as hyaluronic acid (HA), calcium hydroxyapatite (CAHA), and poly-L-lactic acid (PLLA) are widely used. The main differences between fat injection and these fillers are as follows.
Convenience and Reversibility
Synthetic fillers are ready-made products that can instantly supplement volume without the need for harvesting. HA fillers in particular have an extremely significant advantage: if the result is unsatisfactory or complications such as vascular occlusion occur, they can be safely dissolved (reset) with the enzyme hyaluronidase. Additionally, HA can last 2–3 years in some areas such as the nose. In contrast, if fat migrates into blood vessels after injection, there is no safe antidote to dissolve it (Moellhoff 2023).
Biostimulation Effect
Fillers also have the effect of stimulating tissue. HA stimulates fibroblasts by physically stretching the extracellular matrix (ECM), promoting collagen production. CAHA and PLLA act as biostimulators that powerfully promote long-term collagen generation through subtle foreign body reactions (Crowley 2021).
Safety of Autologous Tissue and Cellular Regeneration
Because fat is the patient's own tissue (autologous), it carries no risk of foreign body reaction, allergy, or rejection (Crowley 2021). Furthermore, fat injection is not merely a "physical filler." Through the action of previously mentioned SVF and adipose-derived stem cells (ASCs), it improves blood flow at the cellular level and fundamentally regenerates the thickness and texture of the dermis. However, compared to fillers, fat engraftment rates are less predictable, and non-engrafted fat carries unique risks of causing cysts, calcification, and nodules (Lv 2020).
6. Risks and Complications (Moellhoff 2023)
Although fat injection is generally considered a safe procedure, "arterial embolism (AE)" resulting from accidentally injecting fat into blood vessels is an extremely serious and catastrophic complication that can lead to blindness, stroke, or even death.
In Moellhoff's systematic review, data from 61 patients who developed arterial embolism after facial fat grafting were analyzed. The average age of affected patients was 33.56±11.45 years, relatively young, and the average injection volume was 21.5±21.5 mL (Moellhoff 2023).
High-Risk Injection Sites
The most common injection sites causing arterial embolism were the glabella or multiple facial areas, affecting 16 of 61 patients (26.2%). This was followed by the temples in 10 patients (16.4%) and the forehead in 9 patients (14.8%) (Moellhoff 2023). These areas are extremely high-risk regions because branches of the ophthalmic artery and internal/external carotid arteries form complex anastomotic networks.
Symptoms and Occluded Vessels
Among 58 patients with recorded initial symptoms, 24 patients (41.4%) reported neurological symptoms, 20 (34.5%) reported visual symptoms, and 13 (22.4%) reported both (Moellhoff 2023).
The breakdown of confirmed occluded vessels (data available for 60 patients) was: ophthalmic artery (OA) occlusion in 26 patients (43.3%), cerebral artery (CA) occlusion (anterior/middle cerebral arteries, etc.) in 11 patients (18.3%), and occlusion of both OA and CA in 14 patients (23.3%) (Moellhoff 2023).
Severe Outcomes and Prevention Strategies
The outcomes are extremely serious. 100% of patients (26 people) who experienced ophthalmic artery (OA) occlusion developed permanent vision loss (blindness). Among 10 patients who experienced cerebral artery (CA) occlusion, 80% (8 people) suffered residual neurological deficits, and among 11 patients with both complications, 63.6% (7 people) suffered from both vision loss and neurological damage. Additionally, 6 patients (Moellhoff 2023) died as a result of embolism.
Because fat embolism has no specific antidote like hyaluronidase, prevention before occurrence is absolutely critical. As preventive measures, it is recommended to use thick blunt needles (cannulas) of 18G or larger to reduce the force of arterial penetration, and to inject slowly at low pressure in small amounts using a 1mL syringe (retrograde injection) (Moellhoff 2023). Injection of 0.1 mL or less per site must be strictly maintained.
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7. Summary
Summary of this article
- Fat grafting has evolved from the Coleman technique → MAFT → Nanofat, expanding its role from "filling" to "tissue regeneration"
- By using different fat sizes—millimeter, micrometer, and nanometer—we can replenish fat at anatomically appropriate depths from the deep layers to the dermis
- Average graft survival rate is 47% (Lv 2020) with significant individual variation, improving to 63% with a second injection
- The advantages are the safety and regenerative effects inherent to autologous tissue, but the risk of arterial embolism leading to blindness and cerebral infarction must never be underestimated
- The practitioner's anatomical knowledge and strict adherence to low-pressure, small-volume injection are key to maximizing benefits and minimizing risks
If you have any concerns, please feel free to consult with us first.
References
- Azoury S, Shakir S, Bucky L, et al. Modern Fat Grafting Techniques to the Face and Neck. Plastic & Reconstructive Surgery. 2021DOI
- Coleman S. Structural Fat Grafting: More Than a Permanent Filler. Plastic & Reconstructive Surgery. 2006DOI
- Egro F, Roy E, Rubin J, et al. Evolution of the Coleman Technique. Plastic & Reconstructive Surgery. 2022DOI
- Trevidic P, Sykes J, Criollo-Lamilla G, et al. Filler Complications and the Role of Hyaluronidase. Aesthetic Surgery Journal. 2022DOI
- Wei H, Gu S, Liang Y, et al. Nanofat-Derived Stem Cells with Platelet-Rich Fibrin for Facial Rejuvenation. Oncotarget. 2017DOI
- 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
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 instruction and education across Zetith Beauty Clinic. He specializes in precision aesthetic medicine based on anatomical evidence, pursuing natural results tailored to each patient's skeletal structure and tissue characteristics.