Paolo Erba

Angiogenesis in Wounds Treated by Microdeformational Wound Therapy

BACKGROUNDnMechanical forces play an important role in tissue neovascularization and are a constituent part of modern wound therapies. The mechanisms by which vacuum assisted closure (VAC) modulates wound angiogenesis are still largely unknown.nnnOBJECTIVEnTo investigate how VAC treatment affects wound hypoxia and related profiles of angiogenic factors as well as to identify the anatomical characteristics of the resultant, newly formed vessels.nnnMETHODSnWound neovascularization was evaluated by morphometric analysis of CD31-stained wound cross-sections as well as by corrosion casting analysis. Wound hypoxia and mRNA expression of HIF-1α and associated angiogenic factors were evaluated by pimonidazole hydrochloride staining and quantitative reverse transcription-polymerase chain reaction (RT-PCR), respectively. Vascular endothelial growth factor (VEGF) protein levels were determined by western blot analysis.nnnRESULTSnVAC-treated wounds were characterized by the formation of elongated vessels aligned in parallel and consistent with physiological function, compared to occlusive dressing control wounds that showed formation of tortuous, disoriented vessels. Moreover, VAC-treated wounds displayed a well-oxygenated wound bed, with hypoxia limited to the direct proximity of the VAC-foam interface, where higher VEGF levels were found. By contrast, occlusive dressing control wounds showed generalized hypoxia, with associated accumulation of HIF-1α and related angiogenic factors.nnnCONCLUSIONSnThe combination of established gradients of hypoxia and VEGF expression along with mechanical forces exerted by VAC therapy was associated with the formation of more physiological blood vessels compared to occlusive dressing control wounds. These morphological changes are likely a necessary condition for better wound healing.

Foam pore size is a critical interface parameter of suction-based wound healing devices.

Background: Suction-based wound healing devices with open-pore foam interfaces are widely used to treat complex tissue defects. The impact of changes in physicochemical parameters of the wound interfaces has not been investigated. Methods: Full-thickness wounds in diabetic mice were treated with occlusive dressing or a suction device with a polyurethane foam interface varying in mean pore size diameter. Wound surface deformation on day 2 was measured on fixed tissues. Histologic cross-sections were analyzed for granulation tissue thickness (hematoxylin and eosin), myofibroblast density (&agr;-smooth muscle actin), blood vessel density (platelet endothelial cell adhesion molecule-1), and cell proliferation (Ki67) on day 7. Results: Polyurethane foam–induced wound surface deformation increased with polyurethane foam pore diameter: 15 percent (small pore size), 60 percent (medium pore size), and 150 percent (large pore size). The extent of wound strain correlated with granulation tissue thickness that increased 1.7-fold in small pore size foam–treated wounds, 2.5-fold in medium pore size foam–treated wounds, and 4.9-fold in large pore size foam–treated wounds (p < 0.05) compared with wounds treated with an occlusive dressing. All polyurethane foams increased the number of myofibroblasts over occlusive dressing, with maximal presence in large pore size foam–treated wounds compared with all other groups (p < 0.05). Conclusions: The pore size of the interface material of suction devices has a significant impact on the wound healing response. Larger pores increased wound surface strain, tissue growth, and transformation of contractile cells. Modification of the pore size is a powerful approach for meeting biological needs of specific wounds.

The reconstructive matrix: a new paradigm in reconstructive plastic surgery.

Technology has dramatically altered paradigms and doctrines in modern medicine. In plastic surgery, there has been an explosion of medical knowledge and innovation resulting in a myriad of potential reconstructive options. Since the Edwin Smith Papyrus,1 treatment paradigms have facilitated the decision-making process of the reconstructive surgeon. In 1982, Mathes and Nahai proposed the reconstructive ladder, which emerged as a very useful guiding framework for decision-making in plastic surgery.2 As one goes up the rungs of the ladder, an increasingly complex choice of surgical procedures is described to treat a specific problem. The surgeon should consider using the simplest procedure that effectively solves the problem. Improved surgical techniques increase the reliability of complex reconstruction options that contribute to better functional and aesthetic outcomes. Several articles2–9 refine the concept of the reconstructive ladder, reflecting dissatisfaction with its simplicity. In 1994, Gottlieb and Krieger3 proposed an “elevator” that bypasses rungs of the ladder, emphasizing form and function in decisionmaking. The elevator allows surgeons to select the rung of the ladder that best suits these requirements, regardless of the complexity of the chosen technique. Attempting to emphasize the increasingly popular techniques of microsurgery and tissue expansion, Mathes and Nahai proposed the reconstructive triangle.10 This model emphasizes judgment, experience, and familiarity with reconstructive techniques to select from any of the three corners of the triangle: flap transposition, microsurgery, or tissue expansion. Although it acknowledges the role of the surgeon and the increasing reliability of traditionally difficult reconstructive techniques, the triangle paradigm is criticized as being too “flat”7 because it considers neither the varied complexity of reconstructive procedures nor the aesthetic and functional requirements of each patient. The constant evolution of medical knowledge and the introduction of new technologies are not well incorporated into these models. To provide plastic surgeons with a model that better accounts for today’s constantly evolving technological, medical, and social environments, we propose the concept of the reconstructive matrix.

A morphometric study of mechanotransductively induced dermal neovascularization.

Background: Mechanical stretch has been shown to induce vascular remodeling and increase vessel density, but the pathophysiologic mechanisms and the morphologic changes induced by tensile forces to dermal vessels are poorly understood. Methods: A custom computer-controlled stretch device was designed and applied to the backs of C57BL/6 mice (n = 38). Dermal and vascular remodeling was studied over a 7-day period. Corrosion casting and three-dimensional scanning electron microscopy and CD31 staining were performed to analyze microvessel morphology. Hypoxia was assessed by immunohistochemistry. Western blot analysis of vascular endothelial growth factor (VEGF) and mRNA expression of VEGF receptors was performed. Results: Skin stretching was associated with increased angiogenesis as demonstrated by CD31 staining and vessel corrosion casting where intervascular distance and vessel diameter were decreased (p < 0.01). Immediately after stretching, VEGF dimers were increased. Messenger RNA expression of VEGF receptor 1, VEGF receptor 2, neuropilin 1, and neuropilin 2 was increased starting as early as 2 hours after stretching. Highly proliferating epidermal cells induced epidermal hypoxia starting at day 3 (p < 0.01). Conclusions: Identification of significant hypoxic cells occurred after identification of neovessels, suggesting an alternative mechanism. Increased expression of angiogenic receptors and stabilization of VEGF dimers may be involved in a mechanotransductive, prehypoxic induction of neovascularization.

Poly-N-acetyl glucosamine fibers are synergistic with vacuum-assisted closure in augmenting the healing response of diabetic mice.

BACKGROUNDnVacuum-assisted closure (VAC) has become the preferred modality to treat many complex wounds but could be further improved by methods that minimize bleeding and facilitate wound epithelialization. Short fiber poly-N-acetyl glucosamine nanofibers (sNAG) are effective hemostatic agents that activate platelets and facilitate wound epithelialization. We hypothesized that sNAG used in combination with the VAC device could be synergistic in promoting wound healing while minimizing the risk of bleeding.nnnMETHODSnMembranes consisting entirely of sNAG nanofibers were applied immediately to dorsal excisional wounds of db/db mice followed by application of the VAC device. Wound healing kinetics, angiogenesis, and wound-related growth factor expression were measured.nnnRESULTSnThe application of sNAG membranes to wounds 24 hours before application of the VAC device was associated with a significant activation of wounds (expression of PDGF, TGFβ, EGF), superior granulation tissue formation rich in Collagen I as well as superior wound epithelialization (8.6% ± 0.3% vs. 1.8% ± 1.1% of initial wound size) and wound contraction.nnnCONCLUSIONSnThe application of sNAG fiber-containing membranes before the application of the polyurethane foam interface of VAC devices leads to superior healing in db/db mice and represents a promising wound healing adjunct that can also reduce the risk of bleeding complications.

Septic Tenosynovitis of the Hand: Factors Predicting Need for Subsequent Débridement.

Background: Treatment of septic hand tenosynovitis is complex, and often requires multiple débridements and prolonged antibiotic therapy. The authors undertook this study to identify factors that might be associated with the need for subsequent débridement (after the initial one) because of persistence or secondary worsening of infection. Methods: In this retrospective single-center study, the authors included all adult patients who presented to their emergency department from 2007 to 2010 with septic tenosynovitis of the hand. Results: The authors identified 126 adult patients (55 men; median age, 45 years), nine of whom were immunosuppressed. All had community-acquired infection; 34 (27 percent) had a subcutaneous abscess and eight (6 percent) were febrile. All underwent at least one surgical débridement and had concomitant antibiotic therapy (median, 15 days; range, 7 to 82 days). At least one additional surgical intervention was required in 18 cases (median, 1.13 interventions; range, one to five interventions). All but four episodes (97 percent) were cured of infection on the first attempt after a median follow-up of 27 months. By multivariate analysis, only two factors were significantly associated with the outcome “subsequent surgical débridement”: abscess (OR, 4.6; 95 percent CI, 1.5 to 14.0) and longer duration of antibiotic therapy (OR, 1.2; 95 percent CI, 1.1 to 1.2). Conclusion: In septic tenosynovitis of the hand, the only presenting factor that was statistically predictive of an increased risk of needing a second débridement was the presence of a subcutaneous abscess. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

Discussion. The new reconstructive ladder: modifications to the traditional model.

P lastic surgery provides a dizzying array of reconstructive options for the treatment of complex problems. This often creates confusion for surgeons, patients, and administrators when they try to understand the tradeoffs of the available approaches. The introduction of new technologies further complicates and constantly modifies the decision-making process. Although this wide diversity of available reconstructive approaches makes plastic surgery a fascinating surgical discipline, we also realize that consensus on indications for specific procedures in addition to repetition and standardization can lead to reliability and decreased complication rates for our patients.1 A variety of models, such as “the reconstructive ladder,” assist surgeons in the thought process to find the best solution for a specific reconstructive challenge. Janis et al. reviewed previous reconstructive models and added new technologies such as negative-pressure wound therapies, reconstructive matrices, and tissue expansion inside the wellknown reconstructive ladder. The authors nicely demonstrate how, with improved technology, they can take what previously would have required a complicated reconstructive procedure and transform this into a simpler procedure. We have had similar thoughts when we proposed the reconstructive matrix,2 a three-dimensional model that navigates the axes of surgical complexity, technological sophistication, and patient surgical risk to allow surgeons to determine the appropriate reconstructive procedure (Fig. 1). In comparison with static models that may need to be adjusted further as new operative techniques and technologies are discovered, a matrix has the advantage of being dynamic, as it can be divided into an infinite number of reconstructive solutions. Although simple models explain much of what we do, more sophisticated models are needed to better explain the breadth of surgical options. It will be interesting to observe the future developments in our field and in particular to see how the balance between surgery and technology will change over the next 10 years. Will prosthetics replace extremities reconstruction? Will tissue engineering and cellular therapies be able to reconstruct body parts in the laboratory and replace free tissue transfer? Will improved immunosuppressive therapies lead to an increased safety of composite tissue allografts? How long will complex From the Department of Plastic, Reconstructive, and Aesthetic Surgery, University Hospital of Lausanne, and the Division of Plastic Surgery, Brigham and Women’s Hospital, Harvard Medical School. Received for publication October 8, 2010; accepted October 11, 2010. Copyright ©2010 by the American Society of Plastic Surgeons

160A: MECHANOTRANSDUCTIVE INDUCED RECEPTOR MODULATION AS A PREHYPOXIC MECHANISM OF NEOVASCULARIZATION

Methods: A custom computer controlled stretch device was designed and applied to the backs of C57BL/6 mice (n=38). Mice were stretched continuously with a 50 g force. Seven days after stretching, corrosion casting and three-dimensional (3D) scanning electron microscopy (SEM) were performed to analyze microvessel morphology. Hypoxia was assessed by immunhistochemistry using pimonidazole hydrochloride as an in vivo marker. Western blot analysis of VEGF and mRNA expression of vascular endothelial growth factor receptor 1 (VEGFR1) and 2 (VEGFR2), neuropilin receptor 1 (NP1) and 2 (NP2) was performed.