CONTRACTION OF EXPERIMENTAL SKIN FLAPS

Contraction of experimental skin flaps in loose-skinned animals is a w ell-known hut underestimated phenomenon that in fact may vary in diffe rent circumstances and complicate the calculations of survived and nec rosed areas. A standard abdominal island skin flap design in the rat w as used in this study to investigate the difference between the contra ction rates of necrotic and survived tissues, and to determine its sig nificance in the experimental models. The abdominal island skin flap w as based on the inferior epigastric: neurovascular bundles, and it ext ended from the pubis to the xiphoid and between the both midaxillary l ines. The study was conducted in two steps. In the first step, contrac tion rates of completely necrosed (both pedicles severed) and complete ly survived (vascular pedicles were intact on both sides either with o r without a nerve supply) flaps were assessed in 45 animals. After 1 w eek, area loss was highly significant in both necrosed and survived fl aps (p < 0.001). The rate of contraction was significantly higher in n ecrosed tissues than in survived tissues (p < 0.001), and it was also significantly higher in the neurovascular flaps than in the denervated flaps (p < 0.05). The contraction of all flaps occurred in the vertic al dimension, whereas the horizontal dimension stayed almost the same. In the second step of the study, a unilateral, pedicled abdominal fla p was used, which had a constant necrotic zone on the nonpedicled half , either with or without a nerve supply in 30 animals. After 1 week th e pedicled halves of all flaps were significantly larger than the nonp edicled halves (p < 0.001). Although the total area loss was higher in the neurovascular flaps than the denervated flaps, the difference was not significant statistically (p > 0.05). There was no statistically significant difference between the areas of necrosis seen in both grou ps when it was expressed as a proportion of the total flap area (p > 0 .05). However, this insignificant difference became significant when t he amount of necrosis was expressed as a proportion of only the nonped icled flap half, favoring the denervated flaps (p < 0.005). It appears in this study that ultimate proportions of surviving and necrosed tis sues may be inconsistent owing to the variable contraction rates of th ese tissues, and misleading conclusions may appear during the assessme nt of given treatment modalities.