Partial thickness wound: Does mechanism of injury influence healing?

Wound healing is a complex multistep process which is temporally and spatially controlled. In partial thickness wounds, regeneration is possible from the stem cells in the edges of the wound and from the remnants of the epidermal appendages (such as hair follicles and sebaceous glands). This study examines whether the mechanism of injury influences healing of wounds of similar depth. Burn and excisional wounds were created on the back of Hampshire pigs and harvested at 7, 14, 28, 44, 57 and 70days after injury and processed for histology and immunohistochemistry. Quantitative analysis of re-epithelialisation, inflammatory response and thickness of the scar and semi-quantitative analyses of the architecture of the resultant scar were performed and subjected to statistical analysis. Results demonstrated a higher number of neutrophils, macrophages and lymphocytes present in the burn on day 7 compared to the excisional wounds. The inflammatory profile of burn wounds was higher than that of excisional wounds for the first month after injury albeit less marked than on day 7 after injury. Re-epithelialisation was markedly advanced in excisional wounds compared to burn wounds at day 7 after injury, corresponding to the higher number of hair follicles in the underlying dermis of excisional wounds at this time point. The thickness of the neo-epidermis increased with time and at day 70 after wounding, the neo-epidermis of the burn was significantly thicker than the neo-epidermis of the excisional scar. Interestingly, following partial thickness excision of skin, there was neo-dermal reformation albeit with an altered architecture, lacking the normal basket-weave pattern of collagen. The thickness of the dermis of partial thickness excisional scar was greater than that of the adjacent unwounded skin. The neo-dermis of the burn scar was even thicker, with the collagen arranged more compactly and disorganised compared to excisional scar and normal skin. This study provides evidence that the mechanism of injury does influence wound healing and the resultant scarring.