Studies in Fat Grafting

Sir: We read with great interest the articles by Chung et al. and Atashroo et al. entitled “Studies in Fat Grafting: Part I. Effects of Injection Technique on In Vitro Fat Viability and In Vivo Volume Retention” and “Studies in Fat Grafting: Part II. Effects of Injection Mechanics on Material Properties of Fat,” respectively.1,2 Autologous fat is promising as an ideal filler.3 However, the procedure can be tedious, and results vary. The study characterized a novel device, the adipose tissue injector, which improves precision, reduces trauma and, more importantly, produces superior results. We look forward to obtaining one for hands-on experience. Close examination of the study raised some questions that might compromise accurate interpretation of results, which we would like to communicate with the authors. The “modified Coleman technique” is not referenced. The Coleman technique encompasses gentle manual harvest, centrifugation refinement, and slow low-volume retrograde placement of fat.3 The control technique described therein looked quite different. Preinjection fat manipulation was not identical between groups. Specifically, two more transfers (60-cc syringe, to a 10-cc and then to a 1-cc syringe) occurred in the control group. The adipose tissue injector is designed to reduce shear trauma; additional passes through tubing might render the comparison unbalanced.2 The rate of injection is not specified. Coleman emphasizes retrograde delivery at a very low rate (1/10 to 1/30 ml per withdrawal),3 possibly lower than the adipose tissue injector settings (0.5 to 1 cc/second).2 This matters, as slower flow possibly reduces shear force and trauma.2 Two questions arose concerning statistical analysis. First, as the experimental design produced matched readings (the fat of each donor underwent processing three times), repeated measures one-way analysis of variance might better be used. Second, comparison between two groups, carried out when analysis of variance revealed significant differences among the three groups, should be performed with multiple comparison methods for post hoc testing of analysis of variance, rather than with multiple t tests. The latter approach predisposes to type I error (false-positives). Volume retention measured in both groups was lower than that reported by Thanik et al. in a similar model.4 The disparity remains unaddressed, as multiple variables (e.g., donor site, animal species, techniques, and recipient site) were different between them.1,4 Part II of the study measured mechanical properties of fat injected differentially. The adipose tissue injector group more closely resembled minimally processed fat. However, one notes that the test conditions were far different from what the graft will experience in a grafting session. One also wonders whether and to what extent those differences translate into clinical superiority. Despite these issues, the studies were well-designed explorations into the impact of the adipose tissue injector on fat grafting. In addition to the low-shear trauma exerted, it will probably save time and labor, enhance precision and reproducibility of results delivered, and shorten the learning curve of fat grafting. Future improvements might be made to improve compatibility with other fat collection and refinement systems, to provide more control over flow to prevent pool formation, to incorporate real-time monitoring of interstitial fluid pressure,5 and to develop customized cannulas with modified inner surfaces to further reduce shear trauma. The pursuit of more precise, less traumatic, more reproducible, and less strenuous ways of delivering satisfactory results should always be admired, and we hope that the adipose tissue injector will prove to be both a technical success and a business success. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Yihong Jia, M.D. Nanze Yu, M.D. Yang Wang, M.D. Ang Zeng, M.D. Lin Zhu, M.D. Xiaojun Wang, M.D.