Elsevier

Burns

Volume 43, Issue 1, February 2017, Pages 223-231
Burns

Antecedent thermal injury worsens split-thickness skin graft quality: A clinically relevant porcine model of full-thickness burn, excision and grafting,☆☆

https://doi.org/10.1016/j.burns.2016.08.006Get rights and content

Highlights

  • Burn and excisional wounds were grafted and the effect on skin quality compared.

  • Antecedent burn increased skin graft contraction and decreased skin quality.

  • Antecedent burn increased inflammation, neovascularization, and scarring.

  • The model can serve to evaluate future skin replacement or modulation strategies.

Abstract

Current standard of care for full-thickness burn is excision followed by autologous split-thickness skin graft placement. Skin grafts are also frequently used to cover surgical wounds not amenable to linear closure. While all grafts have potential to contract, clinical observation suggests that antecedent thermal injury worsens contraction and impairs functional and aesthetic outcomes. This study evaluates the impact of antecedent full-thickness burn on split-thickness skin graft scar outcomes and the potential mediating factors. Full-thickness contact burns (100 °C, 30 s) were created on the backs of anesthetized female Yorkshire Pigs. After seven days, burn eschar was tangentially excised and covered with 12/1000th inch (300 μm) split-thickness skin graft. For comparison, unburned wounds were created by sharp excision to fat before graft application. From 7 to 120 days post-grafting, planimetric measurements, digital imaging and biopsies for histology, immunohistochemistry and gene expression were obtained. At 120 days post-grafting, the Observer Scar Assessment Scale, colorimetry, contour analysis and optical graft height assessments were performed. Twenty-nine porcine wounds were analyzed. All measured metrics of clinical skin quality were significantly worse (p < 0.05) in burn injured wounds. Histological analysis supported objective clinical findings with marked scar-like collagen proliferation within the dermis, increased vascular density, and prolonged and increased cellular infiltration. Observed differences in contracture also correlated with earlier and more prominent myofibroblast differentiation as demonstrated by α-SMA staining. Antecedent thermal injury worsens split-thickness skin graft quality, likely by multiple mechanisms including burn-related inflammation, microscopically inadequate excision, and dysregulation of tissue remodeling. A valid, reliable, clinically relevant model of full-thickness burn, excision and skin replacement therapy has been demonstrated. Future research to enhance quality of skin replacement therapies should be directed toward modulation of inflammation and assessments for complete excision.

Introduction

The current standard of care for treatment of full thickness burns is early excisional debridement and wound coverage, though this is not always possible [1]. Reasons include delayed presentation due to altered mental status [2], [3], prolonged transport time from remote points of injury [4], prioritization of life-saving treatments and intentional delay to await determination of uncertain injury depth [5]. While all split-thickness skin grafts (STSG) have the potential to contract, clinical observation suggests that antecedent local thermal injury and delayed eschar excision, exacerbate contraction and impair functional and aesthetic outcomes. Few studies, however, have thoroughly investigated the role of antecedent local full-thickness burn on STSG outcomes or the mechanisms that mediate these outcomes.

Several animal models of burn wound healing have been described [6], [7]. Similarities in skin biology between pig and human make porcine models ideal for translational research in both burn wound therapy and hypertrophic scar formation. However, most burn models allow the eschar to spontaneously slough—a practice largely abandoned in acute burn care [8], [9], [10], [11], [12]. Although spontaneous sloughing may be relevant for investigations of therapies to decrease burn progression or burn depth, the presence of burn eschar alters the wound healing micro-environment. Most studies also choose not to follow the wounds long enough to allow proper assessment of scar quality and contracture [13], [14], [15], [16], [17], [18]. The animal model employed in this study differs notably from other porcine burn models because it more closely mimics current clinical strategy: excision of burn eschar followed by coverage with autologous STSG. Specifically, this study compares skin grafts placed on wound beds of similar depth after excision alone versus excision after antecedent burn. These groups were observed longitudinally for 120 days and excision for differences in macro-scale skin quality, histologic appearance and gene expression.

This study provides validation of a clinically relevant porcine model of tangential excision and grafting of burn wounds using both qualitative and quantitative measurements to assess scar quality. Understanding the contribution of antecedent full-thickness burn to STSG scar outcome will be valuable in developing novel strategies that mitigate the effect of burn eschar on STSG quality.

Section snippets

Animals

The use of 11 six-month old cross-bred female Yorkshire pigs (Midwest Research Swine, Gibbon, MN) was reviewed and approved by Institutional Animal Care and Use Committees (IACUC) at the United States Army Institute of Surgical Research (USAISR, JBSA Fort Sam Houston, TX). This study was conducted in compliance with the Animal Welfare Act, the implementing Animal Welfare Regulations, and the principles of the Guide for the Care and Use of Laboratory Animals. All animals received care in

Collagen stain confirmed full-thickness burn

Burn depth was assessed by three methods: (1) Hematoxylin-Eosin (H&E) stain (2) Masson’s Trichrome stain (MTS) of heat-denatured collagen and (3) TUNEL staining of DNA fragmentation. Tissue biopsies from 7 days post-burn revealed disruption of dermal cellular architecture (H&E) and dark purple MTS staining through the entire dermis (Fig. 1). By contrast, normal unburned skin showed blue, loose and wavy mature collagen. Heat damaged collagen appears red or purple instead of blue which normal

Discussion

Full thickness burns are known to result in poor functional and aesthetic outcomes [24], [25]. However, the contribution of antecedent local full thickness burn to the quality of split thickness skin grafts is not well described. Based on clinical observation, the presence of antecedent burn appears to worsen the outcome of split thickness skin graft. Function-limiting contractures and hypertrophic scars necessitating years of reconstructive operations [26] are common and serve to highlight the

Conclusion

Grafts placed on tangentially excised burn wounds result in worse skin graft quality than those placed on non-burned excisions of the same depth. Acute and chronic inflammation, failure of microvascular regression, sub-lethal cellular injury and disordered collagen production are likely contributors to the poor functional and aesthetic outcomes seen clinically. This model provides a valuable tool for objective in vivo evaluation of current and future skin replacement technologies. Further

Conflict of interests

The authors declare no conflict of interests.

Acknowledgements

The authors would like to express their sincere gratitude to James K. Aden, PhD for his assistance with statistical analysis of the data and Lingamanaidu V. Ravichandran, PhD for his editorial assistance and preparation of the manuscript.

This study was funded by the Department of Defense (DoD) and was supported in part by an appointment to the Postgraduate Research Participation Program at the U.S. Army Medical Research and Materiel Command by the Oak Ridge Institute for Science and Education

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    This study has been conducted in compliance with the Animal Welfare Act, the implementing Animal Welfare Regulations, and the principles of the Guide for the Care and Use of Laboratory Animals.

    ☆☆

    The opinions or assertions contained herein are the private views of the authors are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.

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