DEVELOPMENT AND EVALUATION OF AN IN-VIVO MOUSE MODEL FOR STUDYING MYOCUTANEOUS FLAP MICROCIRCULATION AND VIABILITY BEFORE AND AFTER SUTURING OR STAPLING

A model was developed in albino hairless mice to study microcirculatio n and viability of dorsal distally based myocutaneous flaps. The effic acy of this model was tested in 120 mice by evaluating the effects of excessive crimping and tension attributed to Proximate or Signet stapl es or to simple or mattress nylon sutures. Microhemodynamics were asse ssed using computer-assisted intravital videomicroscopic and electro-o ptical methods. Volumetric rates of blood flow were calculated within terminal arterioles from measurements of internal diameter and mean ce nterline cellular velocity. The viability was determined on day 5 by m easuring the areas of necrosis (mm(2)) along the cut edges of these fl aps. In 80 mice, flaps were elevated and examined at 0 h and then agai n at 24 or 48 h. There were 40 mice in each of these disturbed groups. In a third group of 40 mice, flaps were raised at 0 h without videomi croscopic examination at 0, 24, or 48 h (undisturbed group). All flaps were stapled or sutured to the original donor site with one of the fo ur methods of closure. The results of this study indicate that sutures produce the highest incidence of necrosis at 5 days when compared to staples in the undisturbed groups of mice. However, no significant dif ferences in necrosis were observed when flaps were disturbed at 48 h d espite videomicroscopic evidence of depressed blood flow along their c ut edges. In contrast, results at 24 h were equivocal and statisticall y not significant. These data suggest that the phenomenon of delay and /or flap recirculation following removal and reapproximation of suture s or staples drastically improves perfusion and viability of disturbed flaps. It is also concluded that the homozygous hairless mouse model presents reliable vascular anatomy and that flap survival lengths can consistently be reproduced experimentally. Since color and hair distri bution are similar to those of human skin and simulate the surgical fl aps utilized clinically, the albino hairless mouse flap is judged to b e a valuable model for investigating microvascular function and flap v iability in response to surgical and mechanical factors.