Preformation of microvascular composite free flaps in the rat as an animal model.

For optimal reconstruction of large defects after tumor surgery of the head and neck, composite flaps may be necessary. We describe the design of microsurgically reanastomosed composite skin flaps, using porous polyethylene or titanium implants as a "back side" in an animal model. The epigastric skin of 48 healthy adult Wistar rats was prepared for the subdermal insertion of porous polyethylene implants (pore size: 100-200 microns) and titanium mesh implants having different forms and sizes. Two to 6 weeks after this procedure the flaps were lifted, transposed to the other side and the epigastric vessels were reanastomosed microsurgically. Eighty-three per cent of the skin flaps containing the titanium implants survived when the transplantation occurred 2 weeks after insertion of the implants. Concurrently all flaps with the implanted porous polyethylene (1 mm thick) showed signs of skin necrosis. Survival of the polyethylene loaded flaps improved to 50% when the flaps were left 4 weeks at the donor site. The influence of the implant form on the survival of the flaps was investigated with different implant shapes with flap necrosis being greatest when concave implants were used. Histopathological evaluation of the titanium flaps showed a thin capsule around the implants and a minimal inflammatory reaction. All porous polyethylene implants resulted in a pronounced chronic infection. Transplantation of flaps containing perforated metals (such as the titanium mesh) was possible 2 weeks after insertion of the implant, whereas neovascularization of flaps with porous material required more than 4 weeks growth in situ to ensure at least a 50% viability of the skin. An advantage of the metal implants is the possibility of its use in correcting form by modelling.