197. Investigating the Effects of Intramuscular Fat Grafting on New Muscle Formation Using Nude Mice

PURPOSE: Intramuscular fat grafting, a technique commonly used in aesthetic and reconstructive surgery, involves transferring adipose tissue from undesired areas to enhance volume and contour in muscle tissue. Despite its widespread use, there is limited research on the impact of fat grafting on the recipient muscle. This study aims to investigate the effects of intramuscular fat grafting on limb musculature in mice. METHODS:Part IFive female athymic mice were acclimated. Approximately 300 mL of lipoaspirate was obtained and rinsed with cold phosphate-buffered saline (PBS) to remove blood. This process was repeated until the liquid turned clear. The rinsed fat was placed in 50 mL conical tubes. 2 x 50 mL of fat were spun at 3000 RPM for 3 minutes. The top and bottom fractions were collected. Top fat was injected into the right hind leg, while bottom fat was injected into the left hind leg using a 22-gauge needle. Approximately 0.1 cc-0.2 cc of fat was injected aiming for 3-4 quadrants bilaterally in the quadriceps femoris muscle bundles. The mice recovered without complications. Tissue collection for histological analysis was performed at week 2 for two mice and week 6 for three mice. Samples were collected and fixed in 4% paraformaldehyde for 48 hours, and multi-level histological sections were obtained from the injected muscle at varying intervals, ranging from 100-200μm apart, contingent on muscle thickness. Hematoxylin & eosin staining was performed to visualize and identify structures. Part IIA similar methodology to that described in Part I was performed in this part of experimentation to verify the previous findings and observe grafted fat cell viability and muscle formation over a longer timeframe. In this part, nine mice were used, with seven mice receiving fat injections and two receiving saline injections, and tissue collection was performed at 12 weeks. Additionally, Ex vivo muscle function was assessed using muscle strength evaluation with stretching. RESULTS:Part I Histological analysis revealed new muscle fibers after 6 weeks, suggesting muscle regeneration/formation. At 6 weeks, fat grafts demonstrated viability with minimal necrosis. Collagen formation around the fat grafts was evident at 2 weeks. Part IIFat grafts demonstrated viability at 12 weeks in six out of seven mice. Histological analysis revealed new muscle formation after 12 weeks, however muscle necrosis was present in one leg in one mouse. Muscle stretching did not show significant differences among the four legs per group. However, top fat graft in below the knee muscles did have over two times higher strength, although this finding was not statistically significant. CONCLUSION: The preliminary findings show promise for muscle formation following intramuscular fat grafting. We hope to conduct a third part of this study which will further assess intramuscular fat graft viability and retention, in vivo muscle function and strength, and the safety profile of intramuscular fat grafting in various anatomical locations (e.g., thigh, calf, upper arm).