Use of free interpositional vein grafts as pedicles for prefabrication of skin flaps

Survival rates and risk factors for failure using an interposition vein graft for fingertip amputations with segmental vessel defects

PURPOSE

This study aimed to compare survival rates and risk factors of replantation failures using an interposition vein graft in fingertip amputations with segmental vessel defects with those using simple end-to-end anastomosis in amputations.

PATIENTS AND METHODS

Between 2004 and 2015, 776 (647 males and 129 females) with single Zone I or II amputations of digits underwent replantation. Among these, simple end-to-end anastomosis was performed in 698 replantations, while interposition vein grafts were used for either arterial or venous repair or both in 78 amputated fingertips. The survival rate was compared between the groups. Logistic regression analysis was performed to identify risk factors predicting replantation failure in all study subjects.

RESULTS

Among 776 replantations, 713 (91.9%) survived. At latest follow-up, of 698 cases in the simple anastomosis group, 650 (93.1%) survived; of 78 cases in the vein graft group, 63 (80.8%) survived (p > .001). Logistic regression analysis revealed that avulsion type (odds ratio [OR] 3.121; 95% confidence interval [CI], 1.211-8.064; p = .018) and zone II amputation (OR, 2.370; 95% CI, 1.382-4.065; p = .002) were significant risk factors for replantation failure.

CONCLUSION

This study demonstrates that the survival rate (80.8%) of the vein graft in fingertip amputation with segmental vessel defects was shown to be a possible option to increase the survival rates in case with segmental vessel defects where simple anastomosis could not be performed. However, avulsion type and zone II amputation are important risk factors of replantation failures.

Vascularized Tissue Reconstruction in Previously Irradiated Sarcoma Defects

INTRODUCTION

Radiation therapy (RT) is recommended for appropriately selected sarcoma patients to minimize the risk of local recurrence and to maximize outcomes of disease-free survival and function. The purpose of this study was to confirm the safety of vascularized tissue reconstruction in recently irradiated sarcoma defects.

METHODS

A retrospective review of all patients treated by the senior author for sarcoma reconstruction from January 2005 to July 2017 was performed. Two independent reviewers collected data from both electronic and paper medical records. Patients were included if they underwent flap reconstruction (pedicled or free) following sarcoma resection. The safety of neoadjuvant RT was compared with a control group with no previous irradiation using χ(2) analysis.

RESULTS

Fifty-seven patients were included in the study; 35 patients were included in the preoperative RT group, and 22 patients were included in the control group (no previous irradiation). There was no significant difference in wound complications between the 2 groups (infection, dehiscence, hematoma, and seroma). Microvascular complications (arterial thrombosis, venous thrombosis, partial/total flap loss) were also comparable in the free tissue transfer subgroup.

CONCLUSIONS

The current study demonstrates the safety of both pedicled and free flap reconstruction in previously irradiated sarcoma defects. Judicious selection of reconstructive technique and recipient vessels is crucial in obtaining optimal outcomes given the devastating effects of RT on native tissues.

The potential role of telocytes in Tissue Engineering and Regenerative Medicine

Research and ideas for potential applications in the field of Tissue Engineering (TE) and Regenerative Medicine (RM) have been constantly increasing over recent years, basically driven by the fundamental human dream of repairing and regenerating lost tissue and organ functions. The basic idea of TE is to combine cells with putative stem cell properties with extracellular matrix components, growth factors and supporting matrices to achieve independently growing tissue. As a side effect, in the past years, more insights have been gained into cell-cell interaction and how to manipulate cell behavior. However, to date the ideal cell source has still to be found. Apart from commonly known various stem cell sources, telocytes (TC) have recently attracted increasing attention because they might play a potential role for TE and RM. It becomes increasingly evident that TC provide a regenerative potential and act in cellular communication through their network-forming telopodes. While TE in vitro experiments can be the first step, the key for elucidating their regenerative role will be the investigation of the interaction of TC with the surrounding tissue. For later clinical applications further steps have to include an upscaling process of vascularization of engineered tissue. Arteriovenous loop models to vascularize such constructs provide an ideal platform for preclinical testing of future therapeutic concepts in RM. The following review article should give an overview of what is known so far about the potential role of TC in TE and RM.

Vein grafting your way out of trouble: Examining the utility and efficacy of vein grafts in microsurgery

INTRODUCTION

There is limited data on the indications, outcomes, and associated complications with use of interpositional vein grafts (IVG) in microsurgery. This study sought to critically examine and update the utility of this microsurgical technique.

METHODS

All microsurgical cases at a single institution from 2005 to 2011 were examined for use of IVGs in the primary procedure or during take back or salvage attempts. We examined the cohort overall and performed a subgroup analysis by timing of initial IVG.

RESULTS

In the study period, 1718 patients underwent 2368 free flaps. 51 IVGs were utilized in 38 patients (2.2%) and 38 flaps (1.6%). Eight (42.1%) of the primary procedure IVGs (n = 19) were planned preoperatively. Nine total flap losses (24%) occurred when IVGs were utilized, 89% of which occurred in the take back cohort (p = 0.02). However, planned IVG had a 100% success rate, and IVG utilized in the primary procedure overall had a 95% success rate. Importantly, A significantly higher rate of thrombotic events was noted in all primary cases where IVGs were utilized (p = 0.005).

CONCLUSIONS

This study demonstrates that IVGs can be utilized in primary free flap reconstructions with success rates exceeding 95%. However, in salvage procedures, the use of vein grafts does not approach the same rate of success likely due to multiple factors. Yet when utilized appropriately with thrombectomy and resection of the thrombosed vessel to healthy intima, IVGs can provide an important tool for flap salvage.

LEVEL OF EVIDENCE

prognostic/risk category, level II.

Dose-finding study of fibrin gel-immobilized vascular endothelial growth factor 165 and basic fibroblast growth factor in the arteriovenous loop rat model

The angiogenic effects of different concentrations of vascular endothelial growth factor (VEGF) 165 and basic fibroblast growth factor (bFGF) immobilized in a fibrin-based drug-delivery system were quantitatively assessed in the arteriovenous (AV) loop model. An AV loop was created in the medial thigh of 60 rats. The loop was placed in a Teflon isolation chamber and embedded in 500 microL of fibrin gel loaded with VEGF and bFGF in four different concentrations (no growth factor, 100 ng/mL of VEGF, 25 ng/mL of VEGF and bFGF, 100 ng/mL pf VEGF and bFGF). The explantation intervals were 1, 2, and 4 weeks after the initial operation for all groups. Specimens were investigated using (micro-CT) and histological and morphometrical techniques. After 2 weeks, the cross-section area and construct weight were significantly lower with the use of 100 ng/mL of VEGF and bFGF. Micro-CT and histology showed significantly greater vascular density and number of vessels of the constructs at 2 and 4 weeks when 100 ng/mL of VEGF165 and bFGF were applied than in the growth factor-free specimens. The angioinductive effects were dose-dependent, with best results when using 100 ng/mL of VEGF165 and bFGF. The greater tissue formation was accompanied by faster resorption of the fibrin matrix.

Microsurgical arterovenous loops and biological templates: a novel in vivo chamber for tissue engineering

BACKGROUND

Microsurgical tissue engineering is an emerging topic in regenerative medicine. Here we describe a new microsurgical model of bioengineering in rats based on the use of an arterovenous loop (AV) implanted into a commercially available crosslinked collagen/glycosaminoglycan template.

METHODS

The microvascular loop was created between the femoral artery and vein and covered by the template folded onto itself. The chamber was isolated from the outside tissue by an outer silicon layer to impede tissue ingrowth.

RESULTS

At 1-month postimplantation, the tissue chamber was found heavily vascularized, as assessed by laser Doppler perfusion analysis. Histological examination showed that the AV loop was integrated into the collagen matrix of the template and that the whole template was filled with a newly formed soft connective tissue. Most interestingly, the whole scaffold was found heavily vascularized, including the formation of a large number of alpha-SMA-positive arterioles.

CONCLUSIONS

The developed microsurgical chamber provides a highly vascular, isolated tool for in vivo tissue engineering.

Tissue Engineering of an Implantable Bioartificial Hemofilter

The first step in the tissue engineering of an implantable bioartificial kidney is the development of an implant that produces ultrafiltrate to replace glomerular function. A fabricated device containing synthetic hollow hemofiltration fibers was placed around the femoral vascular pedicle in rats, which initiated new tissue formation with a mature and durable neocapillary bed. The transudate fluid produced by this newly formed capillary bed accumulated through the hollow fibers into a subcutaneous port to allow evaluation of the fluid. In its first phase, this study evaluated various hollow fibers and tissue induction processes by the measurement of fluid volume, urea nitrogen, and total protein continuously for 6 weeks. New tissues formed within the implants surrounding the fibers, and the vascular density, vessel sizes, and percent cross-sectional vascular area were assessed by means of histomorphometric analysis after 6 weeks. The volume of fluid formation correlated with both vascular density and fiber membrane surface area. The implant fluid-to-serum ratios demonstrated a permselective filtrate. In a second phase, platelet-derived growth factor and vascular endothelial growth factor versus carrier alone were infused directly into the implants for the first 4 weeks in vivo through osmotic pumps and followed up to 9 weeks. Cumulative implant fluid volumes were significantly greater in the growth factor-treated group than in control animals and were associated with greater numbers of small-caliber blood vessels. These results provide the initial proof of concept in developing a tissue-engineered hemofilter prototype on a small scale in a rodent model.

Angiogenesis in Tissue Engineering: Breathing Life into Constructed Tissue Substitutes

Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ.

Proposed new method for angiographically quantifying neovascularization in prefabricated flaps

Prefabricated flaps have many potential applications in plastic and reconstructive surgery. Despite numerous experimental investigations and clinical applications, a standard quantification procedure for analyzing neovascularization in prefabricated flaps has not yet been established in the literature. In this study, we developed a new method for quantifying neovascularization, using a standard integral line plate including 25 evenly spaced lines corresponding to a 15-cm flap length, which was subsequently analyzed under a 2x magnification loupe. Vessel quantity was determined by counting the total number of times that vessels perfused by Micropaque intersected the integral lines over the entire surface of the flap. This new method was used for quantifying neovascularization in 156 prefabricated flaps, and we concluded that this technique is very simple and useful, allowing precise determination of the amount of neovascularization in prefabricated flaps on angiograms. Based on this principle, the quantification of neovascularization in any size of prefabricated flap can be easily performed using suitably modified integral line plates corresponding to the various flap dimensions.

Tissue engineering skin flaps: which vascular carrier, arteriovenous shunt loop or arteriovenous bundle, has more potential for angiogenesis and tissue generation?

This study was designed to clarify which vascular carrier, the arteriovenous shunt loop or the arteriovenous bundle, has more potential as a vascular carrier for an artificial skin flap in rats. An arteriovenous shunt loop was constructed between the femoral artery and vein using an interpositional artery (group I) or vein (group II) graft. For arteriovenous bundle groups, the femoral artery and vein were used and subdivided into two groups: distal ligation type (group III) and flow-through type (group IV). The vascular pedicle was wrapped with an artificial dermis and implanted beneath the inguinal skin for 4 weeks. For the control group, a folded sheet of artificial dermis without any vascular carrier was embedded. In experiment 1, the volumes of generated tissue within the artificial dermis were measured in the experimental and control groups (n = 5 in each group). In experiment 2, the origin of new blood vessels sprouting from the arteriovenous shunt loop and arteriovenous bundle were evaluated histologically. The volume of generated tissue in the shunt groups was significantly greater than that in the bundle groups (p < 0.01). However, the bundle groups also showed a great potential for producing new tissue. Serial histological studies showed that new capillaries were derived not only from the vasa vasorum of the femoral vessels but directly from the femoral vein in both the shunt and the bundle groups. This "sprouting" was extensively exhibited in the group III. Although the arteriovenous shunt loop showed a greater potential for producing new tissue and capillaries, the distal ligation type of bundle was thought to be an effective and practical vascular carrier for producing a tissue-engineered skin flap.

Formation of new tissue from an arteriovenous loop in the absence of added extracellular matrix

A major requirement for the microsurgical repair of contour defects of the skin, for example, following removal of a skin cancer on the face, is a mass of vascularised subcutaneous tissue. Such tissue can be generated in vivo using basic tissue engineering principles. In previous studies in our laboratory, we have used a model comprising an arteriovenous (AV) shunt loop sandwiched in artificial dermis, placed in a cylindrical plastic growth chamber, and inserted subcutaneously to grow new connective tissue progressively up to 4 weeks. To learn more about the basic growth characteristics with this model, the same AV shunt loop within a chamber without added extracellular matrix was inserted subcutaneously into the groins of rats for 2, 4, or 12 weeks (n = 5 per group). There was a progressive increase in the mass and volume of tissue such that the chamber was two-thirds full after 12 weeks. Histological examination showed that at 2 weeks there was evidence of fibroblast and vascular outgrowth from the AV shunt, with the formation of granulation tissue, surrounded by a mass of coagulated exudate. At 4 weeks the connective tissue deposition was more extensive, with a mass of more mature granulation tissue containing considerable collagen. By 12 weeks there was an extensive, well vascularized mass of mature fibrous tissue. The blood vessels and residual adventitia of the AV shunt were the likely source of growth factors and of the cells which populated the chamber with new maturing connective tissue. A patent AV shunt in an isolated chamber appears to be the minimal requirement for the generation of new vascularized tissue that is potentially suitable for microsurgical transplantation.

New source of vein graft for rabbit experimentation

The present report introduces a new source of vein graft in rabbit experimentation which is long and of large caliber. The average length of available vein was 13.3+/-0.9 cm (mean+/-SD). The average external diameter of the vein was 1.8+/-0.2 mm (mean+/-SD), 1.4+/-0.4 mm (mean+/-SD), and 1.8+/-0.2 mm (mean+/-SD) at the proximal, middle, and distal portions, respectively. The average number of valves throughout the vein was 7+/-1. The vein is anatomically termed the lateral saphenous vein distally and the ischiadic vein proximally, and is superficially located on the lateral aspect of the pelvic limb. Therefore, this vein is easily harvested from the lower crus to the upper-thigh, providing a long length of vein graft for experimental study.

Generation of an autologous tissue (matrix) flap by combining an arteriovenous shunt loop with artificial skin in rats: preliminary report

The present experiment was designed to investigate the possibility of prefabricating a tissue flap in a rat by combining an arteriovenous (A-V) shunt loop with artificial skin dermis (AS). The A-V fistula loop was constructed between the right femoral artery and vein by the interposition of a vein graft and the loop was wrapped with a folded sheet of AS and buried beneath the inguinal skin. In the control group the folded sheet of AS was inserted without a vessel loop and embedded in the inguinal region as in the experimental group. There were three experiments. In experiment 1, the total volume of the generated tissue formed within the AS was calculated after 4 weeks in the experimental and control groups. In experiment 2, the AS in the experimental group was harvested at 2 (group 1) and 4 (group 2) weeks after insertion to assess the change in morphology over time. In experiment 3, full thickness skin grafts were placed over the generated tissue of the experimental groups to investigate the possibility of creating skin flaps. The total volume of tissue generated in the experimental group was significantly greater than in the control group (P< 0.01). Histological and carbon injection studies suggest that the new capillary bed is derived from the graft loop vessels and tissue generation and organisation of the AS were further advanced in group 2 than in group 1. The skin grafts placed over the tissues generated showed complete survival and could be raised as island flaps in both groups.