Silicone occlusive treatment of hypertrophic scar in the rabbit model

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Abstract
Background: Hypertrophic scar formation at sites of healed cutaneous injury often produces functional and esthetic deficits. Treatments have been limited in part by a lack of understanding of scar etiology and the lack of animal models of hypertrophic scarring. Silicone dressing is reported to provide positive outcomes with respect to a reduction in scar hypertrophy and an improvement in color differences, although the exact mechanism is unknown. Objective: We tested the effectiveness of silicone adhesive gel in the reduction of scar hypertrophy in an animal model of scarring. Methods: Silicone adhesive gel was applied to scars in a rabbit ear model of hypertrophic scarring. Scarring in this model, which displays reduced hypertrophy in response to steroid injections and aging similar to that of human beings, was measured by the Scar Elevation Index (SEI), a ratio of the scar height over normal skin, in which readings greater than 1.0 represent a raised scar. Results: SEIs were significantly reduced after 4-week applications of silicone gel (1.15 ± 0.15 vs 1.71 ± 0.33, respectively; P < .001) versus untreated scars. Nonsilicone control dressings did not alter SEIs in comparison with those found for controls. No histologic differences in scar cellularity, inflammation, or matrix organization were found between treatment groups; however, ultrastructural observation revealed numerous vacuoles in basal cells of control and nonsilicone-treated scars that were not found in unwounded skin or silicone gel-treated scars. The similarity in water vapor transmission rates for silicone gel and a nonsilicone dressing eliminated scar hydration as the sole mechanism of action of the silicone dressings. Conclusions: Our findings with the rabbit model demonstrate the effectiveness of silicone gel for hypertrophic scar treatment and confirm the usefulness of this model for further study of the mechanism of occlusion.