Microporous Polylactic Acid Scaffolds Enable Fluorescence-Based Perfusion Imaging of Intrinsic In Vivo Vascularization.

In vivo tissue engineering (TE) techniques like the AV loop model provide an isolated and well-defined microenvironment to study angiogenesis-related cell interactions. Functional visualization of the microvascular network within these artificial tissue constructs is crucial for the fundamental understanding of vessel network formation and to identify the underlying key regulatory mechanisms. To facilitate microvascular tracking advanced fluorescence imaging techniques are required. We studied the suitability of microporous polylactic acid (PLA) scaffolds with known low autofluorescence to form axial vascularized tissue constructs in the AV loop model and to validate these scaffolds for fluorescence-based perfusion imaging. Compared to commonly used collagen elastin (CE) scaffolds, the total number of vessels and cells in PLA scaffolds was lower. In detail, CE-based constructs exhibited significantly higher vessel numbers on day 14 and 28 (d14: 316 ± 53; d28: 610 ± 74) compared to the respective time points in PLA-based constructs (d14: 144 ± 18; d28: 327 ± 34; each p < 0.05). Analogously, cell counts in CE scaffolds were higher compared to corresponding PLA constructs (d14: 7661.25 ± 505.93 and 5804.04 ± 716.59; d28: 11211.75 + 1278.97 and 6045.71 ± 572.72, p < 0.05). CE scaffolds showed significantly higher vessel densities in proximity to the main vessel axis compared to PLA scaffolds (200-400 µm and 600-800 µm on day 14; 400-1000 µm and 1400-1600 µm on day 28). CE scaffolds had significantly higher cell counts on day 14 at distances from 800 to 2000 µm and at distances from 400 to 1600 µm on day 28. While the total number of vessels and cells in PLA scaffolds were lower, both scaffold types were ideally suited for axial vascularization techniques. The intravascular perfusion of PLA-based constructs with fluorescence dye MHI148-PEI demonstrated dye specificity against vascular walls of low- and high-order branches as well as capillaries and facilitated the fluorescence-based visualization of microcirculatory networks. Fluorophore tracking may contribute to the development of automated quantification methods after 3D reconstruction and image segmentation. These technologies may facilitate the characterization of key regulators within specific subdomains and add to the current understanding of vessel formation in axially vascularized tissue constructs.

A single-center retrospective comparison of Duplex ultrasonography versus audible Doppler regarding anterolateral thigh perforator flap harvest and operative times.

INTRODUCTION: We reported on the superiority of preoperative Duplex mapping ("Duplex") over audible Dopplers ("Doppler") in anterolateral thigh perforator (ALT) free flaps for upper extremity reconstruction. To corroborate our findings on a larger cohort, we conducted this present study focusing on surgical efficiency and patient safety. METHODS: 150 consecutive ALT free flaps were divided into 65 cases of preoperative Duplex versus 85 Doppler controls. We first compared patient demographics, operative details, and defect and flap characteristics. We then assessed group differences in the number and course of perforators pursued intraoperatively, flap harvest and operative times, and donor-site complications. Additionally, the impact of the training level of the primary microsurgeon was evaluated. RESULTS: Cases and controls were comparable regarding age (p = .48), sex (p = .81), ASA class (p = .48), and BMI (p = .90). Duplex was associated with an increased likelihood of raising flaps on one single dominant perforator of purely septal course and significant reductions of flap harvest (68 ± 10 min, p < .0001) and operative times (74 ± 16 min, p < .0001), regardless of the experience of the primary microsurgeon. There were strong negative linear correlations between preoperative Duplex and both the flap harvest and operative times (p < .0001). Additionally, while there was no effect on the emergency take-back rate (OR = 1.3, p = .60), revisions were significantly less likely among duplexed patients (OR = 0.15, p = .04). CONCLUSIONS: Preoperative Duplex is associated with a significant reduction in ALT free flap harvest and overall operative times, as well as donor-site revisions as opposed to Doppler planning, regardless of the training level of the primary microsurgeon.

A Retrospective Comparative Functional and Aesthetic Outcome Study of Muscle versus Cutaneous Free Flaps for Distal Upper Extremity Reconstruction.

BACKGROUND: Function and cosmesis are crucial in upper extremity reconstruction. Yet, there persists a lack of outcome evaluations, particularly regarding differences between free flap types. METHODS: In a single-center retrospective analysis, outcomes were compared between patients with cutaneous or muscle free flaps for distal upper extremity reconstruction between 2008 and 2018. The Disabilities of Arm, Shoulder and Hand -Score, Michigan-Hand (MHQ), and Short Form 36 Health Survey (SF-36) Questionnaires were assessed, motor function was quantified, and self-reported measures of cosmesis were compared, including the Vancouver Scar-Scale (VSS), MHQ aesthetics-subscale (MAS), and Moscona's cosmetic validation-score (CVS). RESULTS: One-hundred forty-one cases were identified, with a shift toward cutaneous flaps over the study period. Muscle flaps were used for larger defects (251 vs. 142 cm2, p = 0.008). Losses, thromboses, and donor-site complications were equally distributed. Partial necroses were more frequent in muscle flaps (11 vs. 1%, p = 0.015). Seventy patients with 53 cutaneous versus 17 muscle flaps were reexamined. There was no difference in the timing of flap coverage (after 16 vs. 15 days, p = 0.79), number of preceding (2 vs. 1.7, p = 0.95), or subsequent operations (19/53 vs. 5/17, p = 0.77). Patients with cutaneous flaps showed higher grip strength (25 vs. 17 kg, p = 0.046) and reported better hand function (MHQ: 58 vs. 47, p = 0.044) and general health (SF-36: 70 vs. 61, p = 0.040), as well as more favorable appearance (MAS: 71 vs. 57, p = 0.044, CVS: 77 vs. 72, p = 0.048), and scar burden (VSS: 0 vs. 3, p < 0.001). CONCLUSION: Cutaneous flaps yielded better motor function, self-perceived cosmesis, patient satisfaction, and quality of life in our cohort of distal upper extremity reconstructions.

Concepts in Early Reconstruction of the Burned Hand.

BACKGROUND: Early reconstruction of burn sequelae of the hand can be challenging owing to high goals for functional and aesthetic outcome. A variety of reconstructive procedures with ascending levels of complexity exists and warrants careful indication. METHODS: In this case series, the main reconstructive techniques for reconstruction of burn defects of the hand are described, illustrated, and discussed: split thickness skin grafting (STSG) with fibrin glue, dermal matrices with STSG, distant random pattern (abdominal bridge) flap, distant pedicled flap (superficial circumflex iliac artery flap), and free microvascular tissue transfer (anterolateral thigh flap). An algorithm for decision making in the reconstructive process is proposed. RESULTS: Split thickness skin grafting provides sufficient coverage for partial thickness defects without exposure of functional structures; fixation with fibrin glue avoids unnecessary stapling. Dermal matrices under STSG provide vascularized granulation tissue on full thickness defects and can be used as salvage procedure on functional structures. Distant random pattern or pedicled flaps provide sufficient coverage of large full thickness defects with exposed functional structures but pose some challenges regarding patient compliance and immobilization. Free tissue transfer allows tailored reconstruction of large full thickness defects with exposed functional structures and can be safely and feasibly performed. Secondary and tertiary procedures are needed with more complex techniques; if applied correctly and consequently, all methods can yield favorable functional and aesthetic outcomes. CONCLUSIONS: Reconstruction of the burned hand may require a broad armamentarium of surgical techniques with different levels of complexity, versatility, and applicability. Excellent results can be achieved with the right procedure for the right patient.

A comparative study of preoperative color-coded Duplex ultrasonography versus handheld audible Dopplers in ALT flap planning.

INTRODUCTION: The anterior lateral thigh (ALT) flap's vascular variability can lead to complications. Thus, the accuracy of numerous planning modalities has been studied. The clinical relevance of competing mapping methods, however, remains unknown. Therefore, we compared the impact of color-coded Duplex ultrasonography and handheld audible Dopplers on surgical efficacy and flap safety. PATIENTS AND METHODS: Forty-four ALT flaps were included in this comparative retrospective monocentric study. Twelve patients received Duplex scans and 32 flaps were designed using Dopplers only. Patient, defect, and flap characteristics of both groups were analyzed. The effect of either planning method on the primary outcome variables - flap harvest and operative times (HT, OT), course of perforator dissection, incidence of flap loss, emergent re-explorations, and donor-site revisions - was then assessed. RESULTS: Patient, defect, and flap characteristics were comparable between both groups, including flap size (Doppler: 134 ± 73 cm2 , Duplex: 131 ± 65 cm2 , p = .90). There was no flap loss. Emergent re-explorations (Doppler: 4/32, Duplex: 1/12, p = .70) and donor-site revisions (Doppler: 2/32, Duplex: 1/12, p = .81) were equally distributed. Duplex rendered septal perforator dissection 10 times more likely (Chi-Square = 8.9, p = .003, OR = 9.7), reaching 50% (n = 6/12), as opposed to only 9% in the Doppler cohort (n = 3/32). This allowed for highly significant HT and OT reductions of 89 minutes, respectively (p < .01): from 255 and 383 min (Doppler) to 166 and 294 min (Duplex). CONCLUSIONS: Preoperative Duplex significantly reduces harvest and operative times of ALT flaps.

Venous bypass grafts versus arteriovenous loops as recipient vessels for microvascular anastomosis in lower extremity reconstructions: A matched-pair analysis.

BACKGROUND: Limb salvage in patients with peripheral vascular disease (PVD) and soft tissue defects often requires both a restoration of blood flow to the lower extremity and soft tissue coverage. Outcomes of free tissue transfer may be affected by vein grafts, which can be used for the placement of an autologous venous bypass or an arteriovenous (AV) loop leading to different hemodynamic situations. The purpose of this study was to investigate whether free flap anastomosis to a bypass or an AV loop can be performed with comparable results. METHODS: We performed a matched-pair analysis of 22 patients with PVD undergoing free flap reconstructions of the lower extremity with end-to-side anastomosis to an autologous venous bypass (n = 11, 1 female and 10 male patients) or an AV loop (n = 11, 2 female and 9 male patients). Defects caused by trauma, infection, ulcer, or fasciotomy were reconstructed in each group with 5 muscle-based flaps, 3 parascapular flaps, 2 anterolateral thigh (ALT) flaps, and 1 conjoined latissimus dorsi and parascapular flap. Postoperative complications including thromboses, flap failures, wound complications, and hematomas were compared. RESULTS: Postoperative complication rates including 1 venous pedicle thrombosis (9%vs. 0%, P = 1.0), minor (18% vs. 9%, P = 1.0) and major wound complications (45% vs. 27%, P = .69) as well as hematomas (27% vs. 36%, P = 1.0) did not show relevant differences between the groups. Flap failures were absent in both groups. CONCLUSION: In patients with PVD, autologous venous bypass grafts may be used for end-to-side anastomoses of free flaps, with postoperative outcomes being comparable to AV loop reconstructions.

MicroRNA-regulated pathways of flow-stimulated angiogenesis and vascular remodeling in vivo.

BACKGROUND: Vascular shear stress promotes endothelial cell sprouting in vitro. The impact of hemodynamic forces on microRNA (miRNA) and gene expression within growing vascular networks in vivo, however, remain poorly investigated. Arteriovenous (AV) shunts are an established model for induction of neoangiogenesis in vivo and can serve as a tool for analysis of hemodynamic effects on miRNA and gene expression profiles over time. METHODS: AV shunts were microsurgically created in rats and explanted on postoperative days 5, 10 and 15. Neoangiogenesis was confirmed by histologic analysis and micro-computed tomography. MiRNA and gene expression profiles were determined in tissue specimens from AV shunts by microarray analysis and quantitative real-time polymerase chain reaction and compared with sham-operated veins by bioinformatics analysis. Changes in protein expression within AV shunt endothelial cells were determined by immunohistochemistry. RESULTS: Samples from AV shunts exhibited a strong overexpression of proangiogenic cytokines, oxygenation-associated genes (HIF1A, HMOX1), and angiopoetic growth factors. Significant inverse correlations of the expressions of miR-223-3p, miR-130b-3p, miR-19b-3p, miR-449a-5p, and miR-511-3p which were up-regulated in AV shunts, and miR-27b-3p, miR-10b-5p, let-7b-5p, and let-7c-5p, which were down-regulated in AV shunts, with their predicted interacting targets C-X-C chemokine receptor 2 (CXCR2), interleukin-1 alpha (IL1A), ephrin receptor kinase 2 (EPHA2), synaptojanin-2 binding protein (SYNJ2BP), forkhead box C1 (FOXC1) were present. CXCL2 and IL1A overexpression in AV shunt endothelium was confirmed at the protein level by immunohistochemistry. CONCLUSIONS: Our data indicate that flow-stimulated angiogenesis is determined by an upregulation of cytokines, oxygenation associated genes and miRNA-dependent regulation of FOXC1, EPHA2 and SYNJ2BP.

Sliding free transverse rectus abdominis myocutaneous flap for closure of a massive abdominal wall defect: A case report.

Despite considerable advances in reconstructive surgery, massive abdominal wall defects continue to pose a significant surgical challenge. We report the case of a 72-year-old morbidly obese female patient with Clostridium septicum-related gas gangrene of the abdominal wall. After multidisciplinary treatment and multiple extensive debridements, a massive full-thickness defect (40 cm × 35 cm) of the right abdominal wall was present. The abdominal contents were covered with a resorbable mesh to prevent evisceration. Finally, the composite defect was successfully reconstructed through a contralateral extended free transverse rectus abdominis myocutaneus (TRAM) flap (50 cm × 38 cm). An arterio-venous loop to the superficial femoral vessels using the great saphenous vein was necessary to allow the flap to reach the defect. Postoperatively, a minor wound healing disorder of the flap was successfully treated with split skin grafting. Six month after surgery, the patient presented with a completely healed flap coverage area and a small abdominal hernia without the need of further surgical revision. This case illustrates the use of a sliding free TRAM flap for closure of a massive abdominal wall defect.

Long-Term Outcome after Successful Lower Extremity Free Flap Salvage.

BACKGROUND: Vascular occlusion after free flap surgery has become a rare complication but still poses a major challenge. It necessitates urgent re-exploration, but the logistic challenge to provide sufficient resources for the emergency intervention remains. The aim of this study was to analyze the long-term outcome after successful lower extremity free flap salvage. METHODS: A single-center retrospective study including long-term follow-up was approved by the local ethics committee. From January 1999 to December 2010, a total of 581 free flaps were performed for lower extremity reconstruction. Eighty-six flaps required emergency re-exploration, of which 65 could be salvaged. Fifteen salvaged flaps were excluded from the study because of secondary amputation. Of 50 patients, 29 (6 females and 23 males) were eligible for follow-up. The mean follow-up time was 54.5 ± 32.9 months. Health-related quality of life (Short Form 36 [SF-36]) and scar quality (Vancouver Scar Scale [VSS]) were analyzed. RESULTS: The overall flap survival rate was 94.7% and the total loss rate was 5.3%. The re-exploration rate was 14.8% (86 of 581 flaps). The salvage rate was 75.6% (65 of 86 flaps). Twenty-one free flaps were totally lost (24.4%). Partial flap loss occurred in 12 cases (14.0%); 67.5% of the vascular complications occurred during the first 24 hours, 20.9% between 24 and 72 hours, and 11.6% after more than 72 hours. The mean time from the first signs of impaired flap perfusion to re-exploration was 1.3 ± 0.4 hours, and from free tissue transfer to re-exploration was 16.2 ± 1.9 hours. The overall scar appearance was good with an average VSS score of 4.0 points. The average SF-36 physical component score was 54.4 ± 5.4 and the mental component score was 63.1 ± 10.7. CONCLUSION: Careful monitoring and the opportunity for urgent re-exploration are the key to success for free flaps salvage. Following these principles, an acceptable long-term outcome can be achieved.

Autologous Breast Reconstruction Using a Tensor Fascia Lata/Anterior Lateral Thigh-Freestyle Flap After Extensive Electric Burn: A Case Report.

AIMS: Reconstruction of breasts and chest wall deformities in female patients after severe burn injury is a challenge for reconstructive surgeons. In these patients, neither implant-based procedures nor standard free flaps are sometimes applicable because of limited skin quality and unavailability of donor sites at the abdomen, back, buttock, or medial thigh. METHODS: We present a case of a young female patient with a history of 80 % total body surface area burn after electric high-voltage injury. The burn occurred at the age of 9 years, and during the initial treatment, the right breast required amputation because of deep, full-thickness burn. Because the rigid and instable scar including chronic wound developed and an implant-based breast reconstruction was not feasible, the choice of possible free flaps was limited to the right lateral/proximal thigh. Preoperative computed tomography angiography demonstrated 2 intact perforators branching off the lateral femoral circumflex artery and a combined 17 × 24-cm tensor fascia lata/anterior lateral thigh perforator flap with in-flap anastomosis was transferred to the right breast after wound debridement and histological exclusion of Majolin ulcer in the instable scar. The internal mammary vessels were chosen as recipient vessels, and the donor site was covered with a split-thickness skin graft. RESULTS: The postoperative course was uneventful at the right breast; however, the recipient site healed secondarily at the proximal pole. The resulting breast asymmetry was corrected by lipofilling of the central zone of the reconstructed breast and new definition of the inframammary fold as well as a minor liposuction at the cranial margin of the flap. The patient was very satisfied with the result, and no further correction was necessary. CONCLUSIONS: Autologous breast reconstruction is a valuable option for patients after severe burn injury. However, microsurgical expertise and an individualized and flexible surgical strategy are required for optimal reconstructive results. Computed tomography angiography is helpful for preoperative planning of the procedure.

The conjoined parascapular and latissimus dorsi free flap for reconstruction of extensive knee defects.

BACKGROUND: Extensive soft-tissue defects affecting the knee region pose a significant reconstructive challenge and may require separate or multiple flaps for coverage. We evaluated the conjoined parascapular and latissimus dorsi free flap as an alternative reconstructive option. METHODS: From January 2013 to December 15, 2016 patients (7 female and 8 male) with a mean age of 47.5 years underwent reconstruction of such defects. Causes were trauma (12 cases) and infection (3 cases). The mean defect size was 40.9 × 20.8 cm (range, 21.4×7.3 to 60.1×40.5 cm). The mean defect surface area was 820.0 cm2 (range, 273.2-2,400.4 cm2 ). The conjoined free flap was anastomosed to the femoral vessels in the adductor canal with (3 cases) or without an arterio-venous loop (8 cases), posterior tibial vessels (3 cases), or anterior tibial vessels (1 case). RESULTS: Postoperatively, 10 patients experienced a total of 14 complications, of which 9 (7 patients) were considered major (requiring additional surgery) and 5 (4 patients) minor (conservative treatment). There was no total flap loss. Partial flap loss occurred in 5 patients. Major donor-site complications occurred in 6 patients with impaired wound healing (4 cases), seroma (1 case), and hematoma (1 case). Reconstruction was successful in 14 out of 15 patients during a mean follow-up time of 28.6 months (range, 6.0-52.5 months). Twelve patients were able to walk at the last follow-up visit. CONCLUSIONS: The conjoined parascapular and latissimus dorsi free flap is a large and reliable flap. It allows for simultaneous 1-stage reconstruction of complex and unusually large soft-tissue defects of the knee region.

Evaluation of perfusion by near-infrared fluorescence imaging in late pedicle obstruction of a parascapular flap to the lower extremity: A case report.

Late free flap failures due to pedicle obstruction are rare adverse events. The purpose of this report is to present a case in which the near-infrared indocyanine green video angiography (ICG-NIR-VA) was used to evaluate the perfusion in a compromised fasciocutaneous flap in the late postoperative period. A 55-year-old male patient, who initially suffered from an open tibial fracture, developed concurrent osteomyelitis with fistulae of the proximal tibia requiring excision. Reconstruction was achieved using a parascapular flap of 25 × 8 cm, anastomosed to an arterio-venous (AV) Loop in the adductor canal. On the 2nd postoperative day the patient developed a thrombosis of the AV-Loop. After thrombectomy, the postoperative course was uneventful. Seven weeks postoperatively the patient presented with a mottled, partially bluish and cold flap. Anticoagulation prophylaxis was stopped 2 days earlier. Angiography confirmed a thrombus in the arterial pedicle leading to flap ischemia. Near infrared guided fluorescence imaging revealed a delayed recapillarization of the proximal part of the flap closest to the vascular pedicle, albeit flap overall perfusion remained intact. Thus, no surgical intervention was undertaken. However, anticoagulation and prostaglandin therapy was initiated and the flap was salvaged. Genetic analysis uncovered a polymorphism in the prothrombin genes. The flap remained viable and without further complications until the last follow-up visit at 36 weeks after microsurgical reconstruction. The patient was fully mobilized with complete return to function. Near-infrared guided fluorescence imaging may be a viable tool for the assessment of late fasciocutaneous free flap complications and guide the decision-making process.

Flow Induced Microvascular Network Formation of Therapeutic Relevant Arteriovenous (AV) Loop-Based Constructs in Response to Ionizing Radiation.

BACKGROUND The arteriovenous (AV) loop model enables axial vascularization to gain a functional microcirculatory system in tissue engineering constructs in vivo. These constructs might replace surgical flaps for the treatment of complex wounds in the future. Today, free flaps are often exposed to high-dose radiation after defect coverage, according to guideline-oriented treatment plans. Vascular response of AV loop-based constructs has not been evaluated after radiation, although it is of particular importance. It is further unclear whether the interposed venous AV loop graft is crucial for the induction of angiogenesis. MATERIAL AND METHODS We exposed the grafted vein to a single radiation dose of 2 Gy prior to loop construction to alter intrinsic and angio-inductive properties specifically within the graft. Vessel loops were embedded in a fibrin-filled chamber for 15 days and radiation-induced effects on flow-mediated vascularization were assessed by micro-CT and two-dimensional histological analysis. RESULTS Vessel amount was significantly impaired when an irradiated vein graft was used for AV loop construction. However, vessel growth and differentiation were still present. In contrast to vessel density, which was homogeneously diminished in constructs containing irradiated veins, vessel diameter was primarily decreased in the more peripheral regions. CONCLUSIONS Vascular luminal sprouts were significantly diminished in irradiated venous grafts, suggesting that the interposing vein constitutes a vital part of the AV loop model and is essential to initiate flow-mediate angiogenesis. These results add to the current understanding of AV loop-based neovascularization and suggest clinical implications for patients requiring combined AV loop-based tissue transfer and adjuvant radiotherapy.

Collagen-Elastin and Collagen-Glycosaminoglycan Scaffolds Promote Distinct Patterns of Matrix Maturation and Axial Vascularization in Arteriovenous Loop-Based Soft Tissue Flaps.

INTRODUCTION: Autologous free flaps are the criterion standard for reconstructions of complex soft tissue defects; however, they are limited by donor-site morbidities. The arteriovenous (AV) loop model enables the generation of soft tissue constructs based on acellular dermal matrices with a functional microvasculature and minimal donor site morbidity. The ideal scaffold for AV loop-based tissue engineering has not been determined. METHODS: AV loops were placed into subcutaneous isolation chambers filled with either a collagen-elastin scaffold or a collagen-glycosaminoglycan scaffold in the thighs of rats. Matrix elasticity, neoangiogenesis, cell migration, and proliferation were compared after 14 and 28 days. RESULTS: Mean vessel count and area had increased in both matrices at 28 compared with 14 days. Collagen-elastin matrices showed a higher mean vessel count and area compared with collagen-glycosaminoglycan matrices at 14 days. At 28 days, a more homogeneous vascular network and higher cell counts were observed in collagen-elastin matrices. Collagen-glycosaminoglycan matrices, however, exhibited less volume loss at day 28. CONCLUSIONS: Collagen-based scaffolds are suitable for soft tissue engineering in conjunction with the AV loop technique. These scaffolds exhibit distinct patterns of angiogenesis, cell migration, and proliferation and may in the future serve as the basis of tissue-engineered free flaps as an individualized treatment concept for critical wounds.

Sequential chimeric medial femoral condyle and anterolateral thigh flow-through flaps for one-stage reconstructions of composite bone and soft tissue defects: Report of three cases.

Small recalcitrant non-unions with poor perfusion require reconstruction with vascularized bone flaps. Cases with concomitant large soft tissue defects are especially challenging, since vascularized soft tissue transfer is often indicated and distant microvascular anastomoses may be required. We introduce a sequential chimeric free flap composed of a medial femoral condyle corticoperiosteal flap anastomosed to an anterolateral thigh flow-through flap (MFC-ALT flap) and report its use for reconstruction of small non-unions with concomitant large soft tissue defects in three exemplary patients. Two female and one male patients ages 39-58 years suffered from composite bone and soft tissue defects of the lower extremity and clavicle caused by tumor resection and postoperative radiation resp. infected tibial pilon fracture. The sizes of the soft tissue defects ranged from 15-23 × 4.5-6 cm and the sizes of the bone defects ranged from 1.5-4 × 2-4 cm. Defect reconstructions were performed in all cases with sequential chimeric MFC-ALT flaps with sizes ranging from 2-4 × 1.6-4 cm for the MFC and 21-23 × 7-8 cm for the ALT skin paddles. Functional reconstructions were achieved in all cases resulting in stable unions and soft tissue coverage enabling the patients to bear full weight without assistance on 5-months follow-up. Postoperative course was uneventful and complications were restricted to a small skin necrosis at the suture line in one case. MFC-ALT flaps may be a safe, and effective procedure for one-stage reconstructions of small, irregularly shaped bone defects with concomitant large soft tissue loss or surrounding instable scarring, particularly in cases of recalcitrant non-unions after radiation exposure.

Influences of Macrohemodynamic Conditions on Systemic Microhemodynamic Changes in Burns.

PURPOSE: The clinical course after major burns is characterized by microcirculatory changes and consecutive capillary leakage. However, current clinical monitoring does not properly assess microcirculation, whereas macrohemodynamic changes are continuously evaluated. Here, we assess if macrohemodynamic and microhemodynamic parameters after burn trauma are correlated in a rat model. METHODS: Burn plasma harvested from donor rats 4 hours after thermal injury (30% total body surface area, 100 °C water, 12 seconds) was administered intravenously to healthy animals during 2 hours of intravital microscopy (burn group [BG]). Shamburn plasma (same procedure but water at 37°C) was transferred for negative controls (shamburn group [SBG]). Intravital microscopy was performed at 0, 60, and 120 minutes to assess capillary leakage measuring fluorescein isothiocyanate-albumin extravasation. Macrocirculation was assessed using mean arterial pressure and heart rate, whereas microcirculation was evaluated using red blood cell velocity, venular diameter, venular wall shear rate and plasma extravasation at 0, 60, and 120 minutes in postcapillary venules. RESULTS: Thirty mesenteric venules (16 animals) in SBG and 31 mesenteric venules (15 animals) in BG were observed during intravital microscopy. Mean arterial pressure and heart rate remained within acceptable margins and showed no significant differences, neither within nor between groups. Significant correlations between macrohemodynamic and microhemodynamic conditions were neither observed for BG nor SBG, except from a significant correlation of MAP and plasma extravasation at T60. However, at T120 mesenteric venules in the BG clearly showed microvascular burn edema, whereas venules in SBG did not. CONCLUSIONS: Stabilization of macrohemodynamic conditions may not necessarily have positive effects on microcirculatory derangements-a fact that has not been shown for burns yet, that is-however, well described for sepsis. Further studies are required to show whether distinct monitoring of microcirculation may offer new approaches for burn trauma treatment.

Free Flap Reconstruction of Sternal Defects after Cardiac Surgery: An Algorithmic Approach for Dealing with Sparse Recipient Vessels.

Background: Sparsity of recipient vessels poses a challenge for microsurgical free flap reconstruction of sternal defects following deep sternal wound infection after cardiac surgery. Methods: From January 2013, a standardized algorithm for dealing with sparse recipient vessels was strictly followed. In this retrospective study including 75 patients, we compared operative details, surgical complications, and reconstructive outcomes of patients treated according to this algorithm (group A: January 2013-May 2021; n = 46) with a historical control group (group B: January 2000-December 2012, n = 29). Results: The left internal mammary artery had been harvested for arterial bypass grafting in 40 of 46 cases (87%) in group A and in all cases in group B. The right internal mammary artery (RIMA) and right internal mammary vein (RIMV) were the first choice as recipient vessels. In case of unsuitability of the RIMV, a right cephalic vein (CV) turndown was used for venous outflow. If both RIMA and RIMV proved insufficient, a single-stage arterio-venous loop (AVL) between the CV and subclavian artery (CV-SA AVL), CV and thoracoacromial artery (CV-TA AVL), or subclavian artery and subclavian vein (SA-SV AVL) was established. The algorithmic approach significantly reduced partial flap necrosis [group A: n = 3 (7%) versus group b: n = 7 (24%); P = 0.04], and overall operation time [group A: 360 ±â€…88 min versus group B: 415 ±â€…80 min; P = 0.01]. Conclusions: Standardized approaches improve clinical outcomes in microsurgical free flap sternal reconstruction after cardiac surgery.

Fat Grafts Show Higher Hypoxia, Angiogenesis, Adipocyte Proliferation, and Macrophage Infiltration than Flaps in a Pilot Mouse Study.

BACKGROUND: Over 137,000 breast reconstructions are performed annually by American Society of Plastic Surgeons (ASPS) members. Vascularized flaps and avascular lipofilling each account for over 33,000 autologous reconstructions. Although clinical and experimental observations suggest biologic differences with diverging effects on locoregional tumor control, comparative animal models are lacking. The authors standardized existing techniques in immunocompetent mice, laying the foundation for in vivo models of autologous breast reconstruction combinable with orthotopic tumor implantations. METHODS: Twenty-five groin flaps and 39 fat grafts were transferred in female BALB/c-mice. Adipocytes were tracked via Hoechst-Calcein-DiI staining ( n = 2 per group), and postoperative volume retentions were compared via magnetic resonance imaging ( n = 3 per group) on days 1, 11, 21, and 31. Proliferation indices, microvessel densities, tissue hypoxia, and macrophage infiltrates were compared via Ki67, CD31, pimonidazole, and hematoxylin-eosin staining on days 5, 10, 15, 20, and 30 ( n = 4 per group). RESULTS: Viable adipocytes were present in both groups. Graft volumes plateaued at 42.7 ± 1.2% versus 81.8 ± 4.0% of flaps ( P < 0.001). Initially, grafts contained more hypoxic cells (day 5: 15.192 ± 1.249 versus 1.157 ± 192; P < 0.001), followed by higher proliferation (day 15: 25.2 ± 1.0% versus 0.0 ± 0.0%; P < 0.001), higher microvessel numbers (day 30: 307.0 ± 13.2 versus 178.0 ± 10.6; P < 0.001), and more pronounced macrophage infiltrates (graded 3 versus 2; P < 0.01). CONCLUSION: This comparative murine pilot study of vascularized flaps versus avascular lipofilling suggests differences in volume retention, proliferation, angiogenesis, hypoxia, and inflammation. CLINICAL RELEVANCE STATEMENT: The biological differences of fat grafting versus flap transfer are not fully understood because no single comparative experimental model has been established to date. The authors present the first comparative small animal model of both techniques, which will allow the gaining of deeper insights into their biological effects.

Tissue engineering and regenerative medicine -where do we stand?

Tissue Engineering (TE) in the context of Regenerative Medicine (RM) has been hailed for many years as one of the most important topics in medicine in the twenty-first century. While the first clinically relevant TE efforts were mainly concerned with the generation of bioengineered skin substitutes, subsequently TE applications have been continuously extended to a wide variety of tissues and organs. The advent of either embryonic or mesenchymal adult stem-cell technology has fostered many of the efforts to combine this promising tool with TE approaches and has merged the field into the term Regenerative Medicine. As a typical example in translational medicine, the discovery of a new type of cells called Telocytes that have been described in many organs and have been detected by electron microscopy opens another gate to RM. Besides cell-therapy strategies, the application of gene therapy combined with TE has been investigated to generate tissues and organs. The vascularization of constructs plays a crucial role besides the matrix and cell substitutes. Therefore, novel in vivo models of vascularization have evolved allowing axial vascularization with subsequent transplantation of constructs. This article is intended to give an overview over some of the most recent developments and possible applications in RM through the perspective of TE achievements and cellular research. The synthesis of TE with innovative methods of molecular biology and stem-cell technology appears to be very promising.

Conditional transgenic expression of fibroblast growth factor 9 in the adult mouse heart reduces heart failure mortality after myocardial infarction.

BACKGROUND: Fibroblast growth factor 9 (FGF9) is secreted from bone marrow cells, which have been shown to improve systolic function after myocardial infarction (MI) in a clinical trial. FGF9 promotes cardiac vascularization during embryonic development but is only weakly expressed in the adult heart. METHODS AND RESULTS: We used a tetracycline-responsive binary transgene system based on the α-myosin heavy chain promoter to test whether conditional expression of FGF9 in the adult myocardium supports adaptation after MI. In sham-operated mice, transgenic FGF9 stimulated left ventricular hypertrophy with microvessel expansion and preserved systolic and diastolic function. After coronary artery ligation, transgenic FGF9 enhanced hypertrophy of the noninfarcted left ventricular myocardium with increased microvessel density, reduced interstitial fibrosis, attenuated fetal gene expression, and improved systolic function. Heart failure mortality after MI was markedly reduced by transgenic FGF9, whereas rupture rates were not affected. Adenoviral FGF9 gene transfer after MI similarly promoted left ventricular hypertrophy with improved systolic function and reduced heart failure mortality. Mechanistically, FGF9 stimulated proliferation and network formation of endothelial cells but induced no direct hypertrophic effects in neonatal or adult rat cardiomyocytes in vitro. FGF9-stimulated endothelial cell supernatants, however, induced cardiomyocyte hypertrophy via paracrine release of bone morphogenetic protein 6. In accord with this observation, expression of bone morphogenetic protein 6 and phosphorylation of its downstream targets SMAD1/5 were increased in the myocardium of FGF9 transgenic mice. CONCLUSIONS: Conditional expression of FGF9 promotes myocardial vascularization and hypertrophy with enhanced systolic function and reduced heart failure mortality after MI. These observations suggest a previously unrecognized therapeutic potential for FGF9 after MI.