Optimizing Autologous Fat Injection for Vocal Fold Medialization: Can We Improve Predictability

Glottic insufficiency can result from vocal fold paralysis, paresis, atrophy, sulcus vocalis, or scarring. Options for medialization/augmentation include synthetic injectable materials, type I thyroplasty, ± arytenoid adduction, and autologous fat injection. Autologous fat offers several advantages. Its viscoelastic properties are similar to the lamina propria of the human vocal fold, potentially supporting more natural vibratory function [1]. In addition, because it is delivered via injection, autologous fat avoids the need for an external incision, any associated risk of visible scarring, or implant related complications such as extrusion. Compared to synthetic materials such as hyaluronic acid or calcium hydroxyapatite, autologous fat carries minimal risk of foreign body reactions. Additionally, adipose-derived stem cells may enhance regenerative effects that improve vocal fold pliability and reduce fibrosis [1, 2]. The main disadvantage of autologous fat is its unpredictable rate of absorption, which can lead to under correction, unpredictable long-term voice outcomes, and the need for repeat procedures. Various efforts have been investigated to enhance fat viability and reduce the need for repeat procedures. This best practice article reviews recent literature on autologous fat harvesting and injection techniques aimed at improving the predictability in its use for vocal fold medialization/augmentation. Based on a recent systematic review by Campagnolo et al., the need for repeat medialization procedures after autologous fat injection ranges from 15% to 40% [1]. This is thought to be mainly due to fat resorption. In a study looking at rates of fat absorption after injection medialization with serial CT scans, Nishio et al. found that within two days of surgery, the residual volume of fat in the paraglottic space decreases to 63.9%, and stabilized at approximately 30% by 3 months, remaining stable for up to 24 months [3]. In a separate CT-based study of basic fibroblast growth factor-enhanced fat injections, Tamura et al. reported a mean residual volume of around 20% at 8 months [2]. Initial fat loss is thought to occur through extrusion at the injection site immediately post-injection [3]. Techniques proposed to minimize this include the use of fibrin glue, applying pressure to the puncture site for five minutes, or using small sized endotracheal tubes [3]. For the injection itself, many authors recommend devices such as Brünings-type syringes or electromotor-controlled injectors with an 18–19 gauge needle to enable gradual and controlled delivery of fat into the paraglottic space [1-3]. Given both early fat loss and resorption over time, overcorrection is widely recommended. A systematic review and meta-analysis by Haddad et al. reported a pooled mean injection volume of 1.3 mL (95% CI 0.92-1.69 mL), with most authors performing an average overcorrection of about 30% [4]. These figures are largely based on surgical experience rather than quantitative studies, but they reflect the consistent observation that injected fat volume decreases substantially after surgery. The volume of fat injected typically ranges from 0.5 to 2.0 mL per vocal fold, depending on the degree of atrophy and the size of the glottic gap [1]. In a recent retrospective series of 73 patients, Umeno et al. compared low-volume (< 2.5 mL; mean 2.0 mL) and high-volume (> 2.5 mL; mean 4.3 mL) fat injections [5]. Of the five patients who required re-injection, four were from the low-volume group, while only one was from the high-volume group. The high-volume group also demonstrated significantly greater improvements in mean phonation time, pitch perturbation quotient, and normalized noise energy. Injection volumes in their study were guided by achieving a visible 20%–30% bulge of the vocal fold. However, the actual amount of fat required to reach this target varied between patients, suggesting that achieving a consistent medialization effect may depend not only on intramuscular injection but also on adequately filling the paraglottic space to support long-term glottic closure. Several authors have suggested that the method of fat harvesting influences adipocyte viability and may reduce resorption rates. Fat is most often harvested from the peri-umbilical region [1, 3, 5] but many other areas have also been reported as donor sites [4]. Tamura et al. noted that buccal fat may offer more uniform cell size, especially in low BMI patients, and greater graft consistency [2]. Many surgeons inject a small amount of saline or Ringer's lactate with epinephrine into the donor site before harvesting to help separate the fat from surrounding tissue and reduce bleeding. This also allows gentler removal of the fat, which is thought to reduce cell damage and contamination, potentially improving graft consistency and longevity [2-4]. Most authors use low-negative-pressure aspiration with a 10–20 mL syringe and a large-bore (e.g., 18-gauge or 2–3 mm) blunt-tip cannula to minimize adipocyte rupture compared with high-vacuum liposuction [1, 3-5]. In contrast, fat can also be harvested through an open approach, excising a small piece of fat directly through a short incision and mincing it into small cubes [4]. While this approach may reduce mechanical trauma compared to aspiration techniques, it is more invasive and has not been conclusively shown to improve graft viability. Future studies comparing open and liposuction-based harvests could help clarify whether reduced trauma translates into better predictability. Of the various methods and sites proposed for harvesting the fat, none has been shown to produce superior results [1, 4]. After harvesting, the fat is typically processed to remove oil, blood, and excess fluid. In the aspiration method, the syringe is allowed to stand for 5–10 min so the contents separate into three layers: an oil layer from ruptured adipocytes at the top, a middle layer of viable fat, and a bottom layer of blood and tumescent solution. The top and bottom layers are discarded, keeping only the middle layer [4]. Excess fluid can be removed by gentle decantation or by placing the fat on sterile gauze or filter paper to absorb oil and tumescent fluid [1, 4]. While some studies incorporate centrifugation in fat processing, others omit it due to concerns about potential mechanical damage to adipocytes [1]. Although some reports have described rinsing fat with additives such as insulin to improve viability, this has not been widely adopted and was not supported by recent systematic reviews. No processing approach has been proven superior in terms of long-term outcomes or graft survival [1, 4]. Predictable outcomes in autologous fat injection for vocal fold medialization are best achieved by overcorrection, typically around 30% and adjusting intraoperatively to the desired medialization, while ensuring both intramuscular placement and adequate paraglottic filling to maintain glottic closure over time. Gentle harvesting with infiltration, low negative pressure, and processing methods that minimize mechanical trauma are commonly employed to maximize adipocyte viability, although robust clinical evidence directly linking these steps to improved outcomes is limited. The volume of fat injected, particularly higher injection volumes, may play an important role in maintaining long-term medialization. The authors declare no conflicts of interest. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

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