Acute and chronic animal models for excessive dermal scarring: quantitative studies

Excessive scarring in the form of keloids and hypertrophic scars continues to be a clinical problem for some patients. The lack of an animal model for such scarring has been an obstacle to studying the cellular and molecular biology of these entities. Previous observations made by the authors that some surgical scars in the rabbit ear remain raised for months after wounding prompted us to investigate whether the rabbit ear might provide a model by which to study excessive dermal scarring. After establishing the model in preliminary study, 40 excisional wounds, 6 mm in diameter, were created over the ventral surface of rabbit ears. Elevated scars were treated with either intralesional triamcinolone acetonide or saline at day 16 postwounding. On day 22, 25 scar wounds were used for thorough histomorphometric analysis, 15 wounds were eliminated prior to analysis because of invagination of epithelial tissue, which made analysis difficult. Total area of scar and Hypertrophic Index, a ratio comparing scar prominence with the thickness of adjacent unwounded tissue, were measured for 25 (62 percent) of the resulting scars. Both total area of scar and Hypertrophic Index were found to be significantly decreased in the steroid-treated group (p < 0.02 and < 0.03, respectively). In a chronic form of this model, in which larger excisions were taken, an excessive accumulation of both new collagen and cartilage over 9 months was observed. An animal model for excessive dermal scarring that allows quantitation of scar formation and, at an early stage, can be modulated in a predictable way with intralesional corticosteroid treatment is presented. This model may parallel hypertrophic scarring in humans and thus might provide a tool by which to study its pathophysiology and objectively evaluate therapeutic modalities.