Reducing Wound Tension with Undermining or Imbrication-Do They Work?

BACKGROUND: For the noncolonized wound, achieving tension-free, primary wound closure is ideal. Some surgeons advocate imbrication of deeper tissues rather than undermining, posing that imbrication preserves more dermal perfusion while still reducing tension at the wound edge. We sought to determine which technique most reliably reduced wound tension while preserving dermal wound perfusion. METHODS: A total of 5 standardized, symmetrical pairs of full thickness wounds were created on Duroc swine. Wound tension was measured with a Tyrolean tensiometer before and after either method of closure, whereas a speckle contrast imager was used to assess dermal edge perfusion. Skin tension and dermal perfusion were evaluated for statistical significance via paired t tests and a multivariate analysis of variance. RESULTS: There was a significant reduction in wound tension with undermining and imbrication relative to the raw wound tension (5 and 5.9 vs 7.1 N; P < 0.05) yet no significant difference between methods of closure (P > 0.05). There was a significant reduction in dermal perfusion between unwounded skin and the imbricated wound (222 perfusion units [PU] vs 48 PU; P < 0.05) and between the unwounded skin and the undermined wound (205 vs 63 PU; P < 0.05). CONCLUSIONS: We found no significant difference in wound tension between wound undermining or imbrication and a significant decrease in dermal perfusion after imbrication and undermining although the relative decrease in perfusion was greater with imbrication. Wound undermining reduces skin tension with greater relative dermal perfusion to the skin and should be selected over wound imbrication in standard primary wound closure.

Examination of the Early Diagnostic Applicability of Active Dynamic Thermography for Burn Wound Depth Assessment and Concept Analysis.

Despite advances in perfusion imaging, burn wound imaging technology continues to lag behind that of other fields. Quantification of blood flow is able to predict time for healing, but clear assessment of burn depth is still questionable. Active dynamic thermography (ADT) is a noncontact imaging modality capable of distinguishing tissue of different thermal conductivities. Utilizing the abnormal heat transfer properties of the burn zones, we examined whether ADT was useful in the determination of burn depth in a model of early burn wound evaluation. Duroc pigs (castrated male; n = 3) were anesthetized, and two burns were created with an aluminum billet at 3 and 12 seconds. These contact times resulted in superficial partial and deep partial thickness burn wounds, respectively. ADT and laser Doppler imaging (LDI) imaging were performed every 30 minutes postburn for a total of five imaging sessions ending 150 minutes postburn. For ADT, imaging excitation was performed for 42-120 seconds with dual quartz-infrared lamps, and subsequent infrared image capture was performed for 300 seconds. MATLAB-assisted image analysis was performed to determine burn zone region of interest thermal relaxation and characteristic patterns. LDI was performed with a moorLDI system, and biopsies were captured for histology following the 150-minute imaging session. Both ADT and LDI imaging modalities are able to detect different physical properties at 30, 60, 90 120, and 150 minutes postburn with statistical significance (P < 0.05). Resultant ADT cooling curves characterize greater differences with greater stimulation and a potentially more identifiable differential cooling characteristic. Histological analysis confirmed burn depth. This preliminary work confirms that ADT can measure burn depth and is deserving of further research either as a stand-alone imaging technology or in combination with a device to assess perfusion.

Biphasic presence of fibrocytes in a porcine hypertrophic scar model.

The duroc pig has been described as a promising animal model for use in the study of human wound healing and scar formation. However, little is known about the presence and chronology of the fibrocyte cell population in the healing process of these animals. Wounds known to form scar were created on red duroc swine (3" x 3") with a dermatome to a total depth of either 0.06 inches or 0.09 inches. These wounds were allowed to heal completely and biopsies were done at scheduled time points during the healing process. Biopsies were formalin fixed and paraffin embedded for immunohistochemical analysis. Porcine reactive antibodies to CD-45 and procollagen-1 and a human reactive antibody to LSP-1 were used to detect the presence of fibrocytes in immunohistochemistry, an immunocytochemistry. Initial immunohistochemical studies showed evidence of a biphasic presence of fibrocytes. Pigs with 0.06 inches deep wounds showed positive staining for CD-45 and LSP-1 within highly cellular areas at days 2 and 4 after wounding. Additional animals with 0.09 inches deep wounds showed positive staining within similar areas at days 56, 70, and 113 after wounding. There was no immunohistochemical evidence of fibrocytes in skin biopsies taken at days 14, 28, or 42. Procollagen-1 staining was diffused in all samples. Cultured cells were stained for CD-45, LSP-1, and procollagen-1 by immunocytochemistry. These data confirm that fibrocytes are indeed present in this porcine model. We conclude that these cells are present after initial wounding and later during scar formation and remodeling. We believe that this is an evidence of a biphasic presence of fibrocytes, first as an acute response to skin wounding followed by later involvement in the remodeling process, prompted by continued inflammation in a deep partial thickness wound.

Commercially available topical platelet-derived growth factor as a novel agent to accelerate burn-related wound healing.

The authors investigated whether the application of platelet-derived growth factor (PDGF) to donor site wounds would speed healing in a porcine model. In a red duroc pig model, three wounds that were 3 inches × 3 inches were created with a dermatome (0.06-inch depth) on one side of two different animals. These wounds were digitally and laser Doppler (LDI) imaged and biopsied immediately pre- and postwound creation and every 2 days for 2 weeks. A set of identical wounds were subsequently created on the opposite side of the same animals and treated with topical PDGF (becaplermin gel 0.01%, 4 g/wound) immediately on wounding. PDGF-treated wounds were imaged and biopsied as above. Digital images of wounds were assessed for epithelialization by clinicians using an ordinal scale. Perfusion units (PU) were evaluated by LDI. Wound healing was evaluated by hematoxylin and eosin histological visualization of an epithelium and intact basement membrane. First evidence of partial epithelialization was seen in control and PDGF-treated wounds within 7.7 ± 1.4 and 6.4 ± 1.1 days postwounding, respectively (P=.03). Completely epithelialized biopsies were seen in control and PDGF-treated wounds at 11.7 ± 2.6 and 9.6 ± 1.5 days, respectively (P=.02). Clinician evaluation of digital images showed that on day 9, control wounds were, on average, 48.3 ± 18.5% epithelialized vs 57.2 ± 20.2% epithelialized for PDGF-treated wounds. At day 16, control wounds showed an average of 72.9 ± 14.6% epithelialization and PDGF-treated wounds showed an average of 90 ± 11.8%epithelialization. Overall, PDGF-treated wounds had statistically significantly higher scores across all timepoints (P=.02). Average perfusion units as measured by LDI were similar for control and PDGF-treated wounds at time of excision (225 ± 81and 257 ± 100, respectively). On day 2 postwounding, average PU for control wounds were 803 and were 764 for PDGF-treated wounds. Control wounds maintained higher PU values compared with PDGF-treated wounds at all time points and returned to excision PU values by day 12.2 ± 1.1 postwounding. PDGF-treated wounds reached the same values by day 9.7 ± 2.3 (P=.03). The authors conclude that topical PDGF speeds time to epithelialization of partial-thickness wounds in a porcine model as evidenced by histology, clinical appearance, and time to return to prewounding vascularity.

A prospective evaluation of platelet function in patients on antiplatelet therapy with traumatic intracranial hemorrhage.

BACKGROUND: Platelet transfusion is increasingly used in patients with traumatic intracranial hemorrhage (ICH) on aspirin therapy to minimize the progression of ICH. We hypothesized (null) that platelet transfusion in this cohort of patients does not improve platelet function. METHODS: We performed a prospective interventional trail on patients with traumatic ICH on daily high-dose (325 mg) aspirin therapy. All patients received one pack of apheresis platelets. Blood samples were collected before and 1 hour after platelet transfusion. Platelet function was assessed using Verify Now Platelet Function Assay, and a cutoff of greater than 550 aspirin reaction units was used to define functioning platelets (FP). RESULTS: Twenty-eight patients were enrolled in the study. On presentation, 79% (22 of 28) of the patients had nonfunctioning platelets (NFPs), and transfusion of platelets did not improve platelet function as 81% (18 of 22) still had NFP. Of the 22 patients, 4 converted from NFP to FP after transfusion. There was no difference in the progression of ICH (37.5% vs. 30%, p = 0.7) or neurosurgical intervention (12.5% vs. 15%, p = 0.86) between patients with FP and NFP after platelet transfusion. CONCLUSION: Administration of one pack of apheresis platelet did not improve platelet function. In our study, progression of ICH and the need for neurosurgical intervention were independent of platelet function. Further randomized clinical trials are required to assess both the dose dependence effect and role of platelet transfusion in patients on antiplatelet therapy with traumatic ICH. LEVEL OF EVIDENCE: Therapeutic study, level III.

Donor site healing dynamics: molecular, histological, and noninvasive imaging assessment in a porcine model.

Understanding the physiology of donor site healing will lead to advances in how these wounds are treated and may ultimately allow faster healing, more frequent autografting, and more effective care of the burn-injured patient. Unfortunately, a paucity of data exists regarding perfusion metrics over the course of donor site healing. Furthermore, there are no studies that interrelate indices of perfusion with the molecular and cellular processes of donor site healing. Male Duroc pigs were anesthetized and donor site wounds were created using a Zimmer dermatome at a depth of 0.060 inch (1.52 mm). Digital photographs, laser Doppler images, and punch biopsies were obtained before and after excision and on days 2, 4, 7, 9, 11, 14, and 16 until wounds were healed. RNA isolation was performed and quantitative polymerase chain reaction was used to examine differential gene expression over the time course. Formalin-fixed biopsies were embedded in paraffin, sectioned, stained, and examined. Wound surfaces were 83% re-epithelialized by day 16. Perfusion peaked on day 2 then declined, but it remained significantly elevated compared to before excision (P < .05). From day 9 onward, mean perfusion units were not significantly different from baseline (P < .05). Twenty-two representative genes were selected for examination. RNA expression of collagen, tenascin-cytoactin, inflammatory cytokines, remodeling enzymes, growth factors, and Wnt was increased. Inflammatory cells and cytokines were demonstrated histologically. Nuclei per high powered field peaked at day 7 and neodermal thickness increased daily to day 14. A novel porcine model for donor site wound healing that interrelates re-epithelilaizationand perfusion with molecular and cellular indices has been demonstrated.

Treatment with an oxazolidinone antibiotic inhibits toxic shock syndrome toxin-1 production in MRSA-infected burn wounds.

Mortality rates in burn patients increase if they experience complications of infection. Frequently, the organisms associated with such infections are Staphylococci, including antibiotic-resistant species such as methicillin-resistant Staphylococcus aureus. Virulence factor production can further complicate treatment as a localized toxin presence may derail the healing process and allow a more invasive infection, while a toxin that becomes systemic can induce shock and cause host immune disruption. Male rats were anesthetized and subjected to full-thickness burn wounds. One day postinjury, wounds were inoculated with Toxic Shock Syndrome Toxin-1-producing methicillin-resistant S. aureus. Animals were then divided into three treatment groups: vancomycin, linezolid, or positive control. For nine additional days, animals received twice-daily antibiotics and wound assessments, blood draws, and wound biopsies were performed. All animals had wound quantitative cultures that exceeded 1 × 10 colony forming units (CFU) per gram 1 day after inoculation. Linezolid treatment significantly reduced the bacterial counts in the wounds. Positive controls and vancomycin-treated animals had toxins in their wounds by day 5 and this remained throughout the study (ranging from 20-80 ng/ml). Linezolid-treated animals had significant decrease in toxin production (< 5 ng/ml), and in most cases toxins were undetectable. No animals became systemically infected with bacteria at any point during the study. Superantigen production in burn wounds has morbid consequences in terms of long-term wound healing. A S. aureus burn wound infection model was created that allowed the study of the effect of two standard-use antibiotics on local burn wound pathophysiology. Most noteworthy is that low-dose linezolid arrested toxin production in the wound.

Localization of superantigen virulence factors in kidney tissue of animals with Staphylococcus aureus-infected burn wounds.

Gram-positive organisms are often found in association with burn wounds. A paucity of information exists regarding the accumulation and fate of virulence factors from these bacteria. The superantigenic exotoxins produced by Staphylococcus aureus are potent immunomodulating proteins and have also been described to localize in the kidney. The aim of this work was to demonstrate renal accumulation of toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin B (SEB) in a methicillin-resistant S. aureus burn wound infection. Twelve Sprague Dawley rats were subjected to partial-thickness burns (2 × 2 cm) using an aluminum billet. On postburn day 1, the wounds were inoculated with a toxin-producing strain of methicillin-resistant Skin biopsies and serum were obtained on postburn days 3, 6, and 10 along with necropsies for three animals each day. An enzyme-linked immunosorbent assay was used to quantify amounts of TSST-1 and SEB. Immunohistochemistry was used to localize SEB, TSST-1, and cleaved caspase-3 in renal tissue, and quantitative real-time polymerase chain reaction was used to assess erythropoietin and endothelin-1 messenger RNA (mRNA) in renal tissue. Baseline skin and plasma levels of TSST-1 and SEB were not detectable. Skin biopsy TSST-1 levels were detected on all postburn days and peaked at a mean value of 39.35 ng/ml on day 6; SEB was found in the skin and kidney only on postburn days 6 and 10. An enzyme-linked immunosorbent assay of renal tissue for TSST-1 and SEB demonstrated significantly higher (P < .05) mean toxin concentrations on postburn day 10: 10.87 ng/ml for TSST-1 and 0.67 ng/ml for SEB. Immunohistochemistry of renal tissue demonstrated increased stain intensity for SEB, TSST-1, and cleaved caspase-3 over time. Quantitative real-time polymerase chain reaction demonstrated decreased expression erythropoietin mRNA and increased expression of endothelin-1 mRNA relative to negative controls (P < .01). In a burn wound infection model that is nonlethal and lacks bacteremia, TSST-1 and SEB traverse cutaneous wounds and localize to the kidney. These potent virulence factors may contribute to the induction of apoptosis, and may alter homeostasis via renal pathophysiology.

A fitted neoprene garment to cover dressings in swine models.

Domesticated porcine species are commonly used in studies of wound healing, owing to similarities between porcine skin and human skin. Such studies often involve wound dressings, and keeping these dressings intact on the animal can be a challenge. The authors describe a novel and simple technique for constructing a fitted neoprene garment for pigs that covers dressings and maintains their integrity during experiments.