The effect of high intensity focused ultrasound on viability of fat grafts in rats

Fat grafting is one of the highly investigated subjects in plastic surgery field because of its autologous nature and similarity to soft tissue. High amounts of donor site, similarity in consistency to soft tissue, inexpensiveness, fewer comorbidities, and longer durability are the some of advantages of fat grafting. Disadvantages can be listed as unpredictability of graft survival and being affected from the changes in the body fat percentage. Maybe this unpredictability is the main reason why plastic surgeons have the feeling of need to investigate this subject. Survival of fat graft is influenced by procedure of harvesting and processing graft, and the attributes of the recipient site. In this study, we investigated the effect of HIFU (High Intensity Focused Ultrasound) on graft survival when applied prior to fat grafting. 22 male Wistar Albino rat were randomized separated in two groups equally as control and experiment group. 2x1cm area on the frontal region is determined for HIFU application and fat grafting. Experiment group got HIFU application 0th and 7th days and control group got placebo on same days. On the day 14, fat grafts harvested from the inguinal regions of both groups. Grafts were cut into small pieces and standardized as 1cc. Processed grafts were injected into previously determined area in the frontal region with 14-gauge cannula. All subjects were scanned with CT (Computerized Tomography) at weeks 4, 6, 8, 10, and 12 in order to follow up the volume change in specific periods until scarification. Study is terminated at week 12. Weight and volume of the excised fat grafts were measured with precision scale and overflow method respectively. Then, fat graft samples were blindly evaluated by two pathologists histomorphologically and immunohistochemically with light microscope. Immune stains CD34 and perilipin were used as immunohistochemical indicator. Samples were scored semiquantitative as 0(none), 1(mild), 2(moderate), 3(severe) for chronic inflammation, fibrosis, fat necrosis, microcyst, microcyst, foreign body reaction, viable adipocyte count, stem cell count, and vessel count. Experiment group had lesser loss in volume follow-up radiologically and lesser loss in volume and weight macroscopically. There was no significant histopathological difference between two groups. This study shows that HIFU application prior to fat grafting has no negative effect on graft survival, even increases the graft survival.