The burn comb model revisited.

Introduction: The burn comb model is a well-established model for studying secondary burn progression. It creates four rectangular burn surfaces intercalated by three unburned zones prone to secondary burn progression. While burn progression is a tri-dimensional phenomenon, of which the vertical extension from the superficial to deeper tissue layer is clinically most relevant, the models initial focus was mainly on the horizontal surface extension within interspaces. The aim of this study is to evaluate the correlation between horizontal surface and vertical depth burn progression.

Methods: 24 large (400-450 g) Wistar male rats underwent standardized burn injuries using a burn comb. Laser Doppler flowmetry to assess perfusion, planimetric evaluation of burn progression within interspaces and histological analyses assessing burn depth were performed before burn induction (baseline; BL) and after 1 h, as well as after 1, 4, and 7 days. Histological burn depth was graded from superficial (1) to the subcutaneous layer (5). Furthermore, final scarring time and contracture rate were also assessed.

Results: The burn comb resulted in consistent and uniform superficial burns (mean ± SEM burn depth score: 2 ± 0; hour 1) separated by intact but critically perfused interspaces (63 ± 1% of BL; p < 0.05 vs. BL). Tissue damage significantly progressed to the deep dermis within the first day (burn depth score 4.3 ± 0.2; p < 0.05 vs. hour 1), while significant interspace necrosis at the surface did not develop within this time period (4 ± 3% of interspace necrosis; p n.s vs. hour 1). However, interspace necrosis was observed at day 4 (83 ± 3%; p < 0.05 vs. hour 1) and further progressed until day 7 (94 ± 2%; p < 0.05 vs. hour 1).

Conclusion: This study shows the limits of the burn comb model originally described with a discrepancy between horizontal surface and vertical depth progression of the burn injury. We herein propose a necessary refinement of this model to adequately evaluate vertical depth progression using a histological score. This revisited approach focusing on assessment of depth progression of the burn will allow a better evaluation of experimental burn treatments in future.