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 microcirculation and viability of dorsal distally based myocutaneous flaps. The efficacy of this model was tested in 120 mice by evaluating the effects of excessive crimping and tension attributed to Proximate or Signet staples or to simple or mattress nylon sutures. Microhemodynamics were assessed using computer-assisted intravital videomicroscopic and electro-optical methods. Volumetric rates of blood flow were calculated within terminal arterioles from measurements of internal diameter and mean centerline cellular velocity. The viability was determined on day 5 by measuring the areas of necrosis (mm(2)) along the cut edges of these flaps. In 80 mice, flaps were elevated and examined at 0 h and then again 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 videomicroscopic examination at 0, 24, or 48 h (undisturbed group). All flaps were stapled or sutured to the original donor site with one of the four 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 differences in necrosis were observed when flaps were disturbed at 48 h despite videomicroscopic evidence of depressed blood flow along their cut edges. In contrast, results at 24 h were equivocal and statistically not significant. These data suggest that the phenomenon of delay and/or flap recirculation following removal and reapproximation of sutures 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 distribution are similar to those of human skin and simulate the surgical flaps utilized clinically, the albino hairless mouse flap is judged to be a valuable model for investigating microvascular function and flap viability in response to surgical and mechanical factors.