Neovascularization in prefabricated flaps using a tissue expander and an implanted arteriovenous pedicle

Creating prefabricated flaps using tissue expanders in combination with the implantation of maximal blood flow vascular pedicles into suitable tissue areas represents a new tendency in the reconstruction of large skin defects. In 42 Chinchilla Bastard female rabbits weighing 3,700-4,600 g, skeletonized arteriovenous pedicles with maximal blood flow, dissected from the femoral and saphena magna bundles, were implanted underneath abdominal fasciocutaneous flaps. Oval tissue expanders of 250 ml were placed and fixed on the abdominal wall to expand these prefabricated flaps. The evaluation parameters were macroscopic observation, blood analysis, selective microangiography, histology, and scintigraphy. The study results showed that neovascularization in expanded prefabricated flaps was established from newly formed vessels generated from the implanted pedicles and their vascular connections with the originally available vasculature in the flap. After 20 days of prefabrication, the entirety of the expanded prefabricated flaps was perfused by blood flow supplied from newly implanted arteriovenous pedicles. The study indicated that an expanded prefabricated flap can be successfully created by the simultaneous implantation of a maximal blood flow pedicle in combination with flap expansion.     

Prefabrication of skin flaps using vein grafts: an experimental study in rabbits.

Prefabrication provides a new method for creating donor sites which are not limited by natural vascular territories. There are several methods for prefabrication, and these include implantation of greater omentum, blood vessels or muscle flaps. Based on the concept that an arterio-venous (A-V) shunt results in sufficient neovascularisation to support a free flap, we used a rabbit model to investigate the characteristics of these flaps. Prefabrication of an abdominal wall donor site was performed using the left epigastric vein in 20 male New Zealand white rabbits. An 8 x 10 cm skin flap was elevated 10 days after prefabrication, either as an island or a free flap. Survival of the skin flaps exceeded 93% and was independent of position of the vascular pedicle, direction of blood flow, or nature of the flap (island or free flap). Angiograms showed a very rich neovascularisation within the prefabricated flap.     

Gene therapy with adenovirus-mediated VEGF enhances skin flap prefabrication

We investigated the feasibility in rats of enhancing skin-flap prefabrication with subdermal injections of adenovirus-encoding vascular endothelial growth factor (Ad-VEGF). The left saphenous vascular pedicle was used as a source for vascular induction. A peninsular abdominal flap (8 x 8 cm) was elevated as distally based, keeping the epigastric vessels intact on both sides. After the vascular pedicle was tacked underneath the abdominal flap, 34 rats were randomly divided into three groups according to treatment protocol. The implantation site around the pedicle was injected with Ad-VEGF in group I (n = 10), with adenovirus-encoding green fluorescent protein (Ad-GFP) in control group I (n = 14), and with saline in control group II (n = 10). All injections were given subdermally at four points around the implanted vessel by an individual blinded to the treatment protocol. The peninsular flap was sutured in its place, and 4 weeks later, an abdominal island flap based solely on the implanted vessels was elevated. The prefabricated island flap was sutured back, and flap viability was evaluated on day 7. Skin specimens were stained with hematoxylin and eosin for histological evaluation. In two rats from each group, microangiography was performed to visualize the vascularity of the prefabricated flaps. There was a significant increase in survival of prefabricated flaps in the Ad-VEGF group compared to the control groups: Ad-VEGF, 88.9 +/- 6.1% vs. Ad-GFP, 65.6 +/- 9.4% (P < 0.05) and saline, 56.0 +/- 3.4% (P < 0.05). Sections from four prefabricated flaps treated with Ad-GFP revealed multiple sites of shiny deposits of green fluorescent protein around the area of local administration 1 day and 3 weeks after gene therapy. Histological examination done under high-power magnification (x400) with a light microscope revealed increased vascularity and mild inflammation surrounding the implanted vessel in all groups. However, we were unable to demonstrate any significant quantitative difference with respect to vascularity and inflammatory infiltrates in prefabricated flaps treated with Ad-VEGF compared with controls. Microangiographic studies showed increased vascularity around the implanted pedicle, which was similar in all groups. However, vascularization was distributed in a larger area in the prefabricated flaps treated with Ad-VEGF. In this study, the authors demonstrated that adenovirus-mediated VEGF gene therapy increased the survival of prefabricated flaps, suggesting that it may allow prefabrication of larger flaps and have the potential to reduce the time required for flap maturation.     

Neovascularization and free microsurgical transfer of in vitro cartilage-engineered constructs

Cartilage tissue engineering shows to have tremendous potential for the reconstruction of three-dimensional cartilage defects. To ensure survival, shape, and function, in vitro cartilage-engineered constructs must be revascularized. This article presents an effective method for neovascularization and free microsurgical transfer of these in vitro constructs. Twelve female Chinchilla Bastard rabbits were used. Cartilage-engineered constructs were created by isolating chondrocytes from auricular biopsies, amplifying in monolayer culture, and then seeding them onto polycaprolactone scaffolds. In each prefabricated skin flap, three in vitro cartilage-engineered constructs (2 x 2 x 0.5 cm) and one construct without cells (served as the control) were implanted beneath an 8 x 15 cm random-pattern skin flap, neovascularized by implantation of an arteriovenous vascular pedicle with maximal blood flow. Six weeks later, the neovascularized flaps with embedded cartilage-engineered constructs were completely removed based on the newly implanted vascular pedicle, and then freely retransferred into position using microsurgery. Macroscopic observation, selective microangiography, histology, and immunohistochemistry were performed to determine the construct vitality, neovascularization, and new cartilage formation. The results showed that all neovascularized skin flaps with embedded constructs were successfully free-transferred as free flaps. The implanted constructs were well integrated and protected within the flap. All constructs were well neovascularized and showed histologically stability in both size and form. Immunohistology showed the existence of cartilage-like tissue with extracellular matrix neosynthesis.     

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

Pedicles created from a long vein graft increase the scope and applications of prefabricated skin flaps. This study reports the survival and pattern of neovascularization of lower abdominal skin flaps in rabbits based on a pedicle formed by interposition of a long vein graft between the divided ipsilateral femoral artery and vein. Flaps were elevated 2–5 weeks after pedicle implantation and the surviving area quantitated and vascular patterns examined 1 week later. Only 8 out of 35 flaps were greater than 50% alive, the most frequent cause of flap failure being pedicle non-patency. If the pedicle remained patent, complete flap survival was possible as early as 2 weeks after implantation. In non-patent pedicles, recanalization or formation of a new vascular network may, given at least 4 weeks, be sufficient to ensure partial flap survival. The findings indicate that implantation of a long, skeletonized vein graft is an unreliable method of prefabrication of abdominal skin flaps in this model. © 1994 Wiley-Liss, Inc.     

颈胸部预构扩张皮瓣在颜面修复中的应用

目的 探讨建立以旋股外侧动脉降支血管为蒂,以颈胸区皮肤为扩张对象的预构皮瓣技术用于重建颜面.方法 选择严重颜面部烧伤的患者为治疗对象.手术分两期进行.一期手术时,切取以旋股外侧动脉降支为蒂的筋膜瓣,与面动脉或甲状腺上动脉吻合,植入颈胸部皮下,于筋膜瓣下放置皮肤扩张器.扩张完毕后,形成以植入血管为蒂的预构岛状超薄皮瓣,用于面颈部皮肤缺损的修复.术后随访重建颜面的肤色、质地、表情恢复情况.结果 临床治疗9例患者.术中切取筋膜瓣的面积平均为6.3×11.2 cm,经过平均16.7周扩张后,扩张器平均注液1670 ml,预构皮瓣的面积为12 cm x 15 cm～15×32 cm.所有病例面颈部创面均有效覆盖,供瓣区直接拉拢缝合.二期术后皮瓣出现不同的程度静脉回流障碍,2例发生皮瓣远端边缘小部分坏死,3例行蒂部修整.术后随访,转移皮瓣与修复部位周围的皮肤色泽、质地接近,面部表情、形态恢复自然.供区大腿未出现肌力减弱或感觉异常现象.结论 以含旋股外侧动脉降支的筋膜瓣为血管载体,结合组织扩张技术,于颈胸部形成的预构皮瓣是修复颜面部大面积皮肤缺损的有效方法.     

Flap prefabrication and prelamination with tissue-engineered cartilage

In reconstructive surgery, the integration of tissue-engineered cartilage in a prefabricated free flap may make it possible to generate flaps combining a variety of tissue components, to meet the special requirements of particular defects. One aim of the present study was to investigate prefabrication of a microvascular free flap by implanting a vessel loop under a skin flap in a rabbit model. A second aim was to report on the authors' preliminary experiences in prelaminating prefabricated flaps with autologous tissue-engineered cartilage, in terms of matrix development, inflammatory reaction, and host-tissue interaction. The flap was prefabricated by implanting a vessel loop under a random-pattern abdominal skin flap. The tissue-engineered cartilage constructs were made by isolating chondrocytes from auricular biopsies. Following a period of amplification, the cells were seeded onto a non-woven scaffold made of a hyaluronic-acid derivative and cultivated for 2 weeks. One cell-biomaterial construct was placed beneath the prefabicated flap, and two additional constructs were placed subcutaneously and intramuscularly. In addition, a biomaterial sample without cells was placed subcutaneously to provide a control. All implanted specimens were left in position for 6 or 12 weeks. Neovascularization in the prefabricated flap and biomaterial construct was analyzed by angiography. After explantation, the specimens were examined by histologic and immunohistochemical methods. The prefabricated flaps showed a well-developed network of blood vessels between the implanted vessel loop and the original random-pattern blood supply. The tissue-engineered constructs remained stable in size and showed signs of tissue similar to hyaline cartilage, as evidenced by the expression of cartilage-specific collagen type II and proteoglycans. No inflammatory reactions were observed. The physiologic environment of the autologous rabbit model provided favorable conditions for matrix deposition and maturation of the cell-biomaterial constructs. These initial results demonstrated the potential of prefabricating an axial perfused flap, combined with tissue-engineered cartilage, thus creating functionally competent tissue components for reconstructive surgery with minimal donor-site morbidity.     

岛状颞浅血管颈部预制扩张皮瓣修复面部软组织缺损

目的　探讨应用颞浅血管束颈部预制扩张皮瓣修复面部较大软组织缺损的原理及临床应用方法。　方法　 1998年～ 2 0 0 3年 ,对 6例面部瘢痕挛缩的患者 ,将颞浅血管植入颈部扩张皮瓣皮下 ,经 3个月组织扩张 ,形成以颞浅血管为蒂的颈部预制扩张皮瓣 ,移位修复同侧面部软组织缺损。预制扩张皮瓣最大范围为 12 cm× 8cm,蒂长 7～8cm。　结果　术后 6个预制扩张皮瓣 ,移位后有一过性充血潮红 ,均完全成活。修复面颊部及颏部软组织缺损后 ,随访3～ 6个月 ,效果良好。　结论　以颞浅血管颈部预制扩张皮瓣修复面部软组织缺损方法可靠。颞浅血管束与扩张皮瓣接触范围的大小与蒂部所携带皮瓣的面积呈正相关。     

大鼠隐血管束全腹壁预制皮瓣模型的实验研究

目的:探讨一种以大鼠隐血管束为预制血管蒂的全腹壁预制皮瓣模型的设计及应用价值。方法:将18只SD大鼠按Ⅰ期手术与Ⅱ期手术之间的间隔时间2、4、6周分为三组。Ⅰ期手术制备大鼠后肢隐血管束预制血管蒂,Ⅱ期手术切开皮瓣四边,形成以预制隐血管束为蒂的岛状皮瓣。Ⅰ期、Ⅱ期术后观察皮瓣血运,记录皮瓣成活面积及成活率。检测Ⅱ期皮瓣血管蒂旁局部组织中血管内皮生长因子(VEGF)含量,取成活皮瓣制作病例切片,HE染色,计算血管密度(血管数/mm2)。运用统计学方法比较各组间差异。结果:Ⅰ期术后各组大鼠腹部皮瓣全部成活;Ⅱ期术后1周,Ⅰ组皮瓣全部坏死,Ⅱ组、Ⅲ组皮瓣平均成活率分别为(14.68±1.02)%,(16.19±1.71)%(P<0.05);Ⅱ期皮瓣局部组织VEGF平均含量:Ⅰ组243.95±4.37,Ⅱ组240.89±3.11,Ⅲ组239.19±2.61(P>0.05);大鼠平均血管密度6周组较4周组略有增多,但差别不大(P>0.05)。结论:大鼠隐血管束全腹壁预制皮瓣模型,可以作为研究提高预制皮瓣成活率的基础,Ⅰ期手术与Ⅱ期手术之间的时间间隔至少需4周。     

The fasciovascular pedicle for revascularization of other tissues.

A fasciovascular pedicle based on the epigastric vessels was developed in a rat model to determine if it could be used as a "universal carrier" to revascularize a new composite flap. The effects of time course, carrier size, and flap ischemia on the revascularization process were studied. A 2.5 x 4-cm or 1 x 4-cm fascial patch pedicled on the vessels was transferred under bipedicled 2.5 x 4-, 6-, or 8-cm abdominal panniculocutaneous flaps. At different time intervals, the flap was raised as an island flap connected only by it vascular bundle and then sutured back in place. The skin perfusion by dermofluorometry and flap survival were both markedly increased on day 5 (p less than 0.001). The wide carrier had a 93% survival area, whereas the narrow carrier had only 71%. The wide carrier induced relatively faster and better revascularization (p less than 0.05). Moderate ischemia promoted revascularization (p less than 0.01). An india ink injection study and histological examination provided visual evidence of revascularization. This fasciovascular pedicle is a promising model for prefabrication of complex new composite flaps and for studying the process of revascularization between the layers. Based on these findings and further investigations, a thin, prefabricated abdominal free flap was successfully transferred for facial resurfacing in humans.     

Use of fascial grafts as an interface in flap prefabrication: an experimental study.

An experimental study was conducted to investigate whether a fascial graft can be used as an interface between a vascular pedicle and target tissue to augment tissue survival in a prefabricated flap. Thirty-six male Sprague-Dawley rats were divided into three experimental groups according to the type of the recipient bed prepared for the vascular implantation. The left saphenous vascular pedicle was used as the vascular source. A 9 x 9-cm inferiorly based peninsular abdominal flap was elevated in each animal. In group I, the pedicle was tacked beneath the abdominal flap, in which the epigastric fascial layer was untouched. In group II, a 3 x 5-cm graft of epigastric fascia was harvested from the abdominal flaps under loupe magnification. The graft was sutured back into its original position after a 180-deg rotation. The vascular pedicle was then implanted just beneath the center of the fascial graft. In group III, the same size of epigastric fascia was removed in the same manner as group II, exposing the subcutaneous layer for pedicle implantation. Four weeks later, abdominal flaps were raised as island flaps connected only to the saphenous pedicle and were sutured in place. Flap viability was assessed visually on day 7. Overall, the ultimate flap survival in group I was the largest, with some necrotic areas at the periphery of the flaps. In group II, flap survival was typically centralized over the fascial graft, and crescent-shaped necrosis was noted superiorly. In group III, an almost linear pattern of survival overlying the vascular pedicle was observed. The mean surviving flap area of group I (12.13 +/- 1.615 cm2) was statistically greater than that of group II (8.83 +/- 0.663 cm2, p < 0.001) and group III (6.3 +/- 0.815 cm2; p < 0.001). There was a statistically significant difference between the mean flap survival in groups II and III (p < 0.001). Vascular arborization was examined by microangiography, and specimens were processed for histological staining. In group II, vascularization was distributed in a larger area along the fascial graft in comparison with limited vascularization around the pedicle in group III. In this study it was revealed that the interposition of a fascial graft as an interface between the vascular source and the target tissue seems to increase the size of the prefabricated flap.     

Experimental study on axial pedicled composite flap prefabrication with high density porous polyethylene implants: medporocutaneous flap.

Composite flaps including soft tissues with bone or cartilage are widely used in reconstruction of three-dimensional defects, but have some disadvantages. Flap prefabrication with alloplastic implants is an alternative procedure. Axial pattern vascularised high density porous polyethylene (HDPP) implants are capable of sustaining skin grafts. The purpose of this study was to examine the vascularisation pattern of the skin island in a composite flap prefabrication model prepared with vascularised HDPP implants. Forty male Wistar rats divided into four groups were used. A 9.5 x 6 x 2 mm HDPP block was centered on the dissected saphenous pedicle and anchored under the abdominal skin in the experimental group I (n=10). In experimental group II (n=10) saphenous artery and vein were put between the skin and the implant. Thus, the structures were laid as skin, HDPP block, pedicle in experimental group I and skin, pedicle, HDPP block in experimental group II. HDPP block-implanted and pedicle-implanted only groups served as control groups I and II, respectively. Eight weeks after prefabrication, skin islands 1.5 x 5 cm in size incorporated with implants were elevated based on saphenous vessels in the experimental groups and skin islands only based on the pedicle in control group II. Skin islands of the same dimensions were raised as grafts in control group I. Nylon sheets were put under the flaps and grafts to prevent vascularisation from the recipient bed. Flap viability was assessed by measuring the surface area on the 7th day. Total necrosis developed in composite grafts of control group I. Flap survival was higher in experimental group II and control group II (45% and 46.8%) than in group I (29.28%). Histologic studies demonstrated fibrovascular ingrowth into the HDPP implants, except in control group I, with significant inflammatory response and necrosis. Vascularisation of skin and implants from the pedicle was seen also microangiographically. In conclusion, a composite flap prefabrication model including vascularised HDPP implant, skin and vascular carrier was developed. This new flap was termed a 'medporocutaneous flap'.     

血管内皮祖细胞和血管内皮生长因子促进预构皮瓣血管新生作用的比较

目的 比较血管内皮祖细胞(endothelial progenitor cells,EPCs)与血管内皮生长因子(vascular endothelial growth factor,VEGF)在促进预构皮瓣血管新生作用上的差异,探讨EPCs移植提高预构皮瓣存活面积的可行性.方法 分离雄性Wistar大鼠(45只)一侧股血管柬,转位植入腹部皮下,建立预构皮瓣实验模型.将体外诱导分化的EPCs(组Ⅰ,n=15)和VEGF(组Ⅱ,n=15)分别注射于皮瓣局部,对照组仅注射PBS溶液(组Ⅲ,n=15).4周后形成以植入血管为蒂的岛状皮瓣,原位缝合;术后7 d对皮瓣存活率、血管密度计数进行检测.结果 组Ⅰ、组Ⅱ、组Ⅲ的皮瓣存活率分别为(87.26±10.13)%、(66.13±9.9)%、(55.59±13.06)%,组Ⅰ分别与组Ⅱ和组Ⅲ比较,差异均有统计学意义(P<0.001);微血管密度分别为:(38.67±9.52)个/mm~2、(25.83±6.33)个/mm~2、(26.5±5.61)个/mm~2(P<0.05).结论 EPCs促进预构皮瓣血管新生的作用优于VEGF,局部应用骨髓来源的EPCs可以有效地提高预构皮瓣存活面积.     

Impact of tissue expansion on flap prefabrication: An experimental study in rabbits

This study was designed to determine whether tissue expansion after vascular pedicle implantation would increase the survival area of prefabricated skin flaps. In 20 New Zealand white rabbits, the vascular pedicle consisting of the central artery and vein of the left ear was implanted into the neck. At the time of pedicle implantation a subcutaneous pocket was created measuring 5 × 14 cm beneath the implantation site. Tissue expanders of three different sizes and volumes were implanted in the rabbits of three treatment groups. No tissue expander was implanted in the animals of the control group. All flaps were transposed after 3 weeks to the contralateral ear, and flap survival was assessed 1 week later. The increased area of the flap survival was statistically significant in all three treatment groups compared to the nonexpanded flaps (P = 0.003, P = 0.004, P < 0.0001, respectively). In addition there was a statistically significant larger area of survival using a 100-cc expander measuring 5 × 14 cm (the same size as the elevated flap) compared to 40-cc (3 × 5 cm) or to 60-cc (4 × 8 cm) expanders (P < 0.001, P = 0.004, respectively). The one-way analysis of variance and the t-test were used to show statistical differences. We conclude that the time necessary for neovascularisation of the skin flap could be used to expand the tissue, not only increasing the amount of available tissue, but also enhancing the vascularity. © 1996 Wiley-Liss, Inc.     

Prefabrication of combined composite (chimeric) flaps in rats

The purpose of this study was to prefabricate a new combined composite (chimeric) flap that consists of four different tissues. The tissues were prefabricated around two independent pedicles that ultimately join as a single main pedicle. In the inguinal area of 36 rats, the saphenous and the superficial inferior epigastric (SIE) pedicles were dissected and prepared as vascular carriers. A fascial graft and a local muscle flap were wrapped around the saphenous pedicle. The SIE pedicle was then implanted under the abdominal skin to supply a future skin flap. An ear cartilage graft was also inserted under the abdominal skin and adjacent to the implanted SIE pedicle. After allowing 2-, 4-, 6-, and 12-week prefabrication periods in different groups of nine animals, the prefabricated tissues were raised around two pedicles nourished by the femoral pedicle and then transferred. Flap survival was assessed by observation, microangiography and histology. The skin flaps showed survival rates of 52 +/- 17% (mean +/- standard error of the mean), 64 +/- 16%, 86 +/- 11%, and 100 +/- 0% of the total areas in the 2-, 4-, 6-, and 12-week prefabricated flaps respectively. None of the control grafts that were prepared on the contralateral side survived totally. A significant difference was found between the 12- and 2-week (p < 0.008), 12- and 4-week (p < 0.02), and 6- and 2-week (p < 0.05) prefabrication groups. Histologically, fascial and cartilage grafts, and portions of muscle were viable in the 2- and 4-week groups. Also, noticeable necrosis was found in the skin flaps in these groups. The muscle showed mild (at 2, 4, and 6 weeks) and moderate (at 12 weeks) atrophy. After prefabrication for 6 weeks, all tissues demonstrated good survival. This study shows that a combined composite flap can be prefabricated successfully in rats after a 6-week period of prefabrication.     

Vascularization of skin following implantation of an arteriovenous pedicle: implications in flap prefabrication.

In a rat model, a skin flap was fabricated by implantation of a distally ligated arteriovenous pedicle. The femoral artery and vein were implanted as a unit beneath the abdominal skin, a portion of which was later raised as an island flap, based on these vessels. Percentage area of survival, tissue blood flow, and pattern of vascularity were compared in two groups of flaps. In group I, the pedicle to be implanted was dissected with a cuff of surrounding muscle still attached; in group II, the pedicle was skeletonized to the level of adventitia. Flap survival in the two groups was similar (73% vs. 77%), as was skin blood flow (5.4 vs. 5.7 ml/100 g/min). Angiography demonstrated two principal patterns of vascularization: connection between donor and recipient vessels (inoculation), and sprouting and arborization of new vessels. Strengths and limitations of this and other models of flap "prefabrication" are discussed.     

颞顶筋膜岛状瓣植入耳后乳突区预制扩张筋膜皮瓣修复面部皮肤软组织缺损

目的探讨一种较好的修复面部皮肤软组织缺损的手术方法。方法手术分两期进行。一期手术时,以颞浅动静脉为蒂,掀起颞顶浅筋膜岛状瓣,沿同侧发际线切开,在耳后乳突区皮下剥离,形成适当大小的囊腔,将颞顶筋膜瓣转移至囊腔内,适当固定,于筋膜瓣下放置皮肤扩张器;扩张完毕后,取出扩张器,以颞浅动静脉为蒂,掀起耳后乳突区预制岛状筋膜皮瓣,用于面部皮肤缺损的修复。结果自1999年以来,临床应用9例,其中面部黑痣2例,面部血管瘤2例,面部瘢痕5例。颞顶筋膜岛状皮瓣蒂长5.5~7cm,平均6.2cm,筋膜瓣面积4cm×3cm~7cm×7cm,平均5.7cm×4.9cm,预制筋膜皮瓣面积为5cm×5cm~8.0cm×7.5cm,平均6.4cm×6.1cm;术后皮瓣全部成活,供瓣区直接拉拢缝合者5例,另行皮片移植修复者4例。结论颞顶筋膜皮瓣血管蒂长,转移方便,血运丰富,耳后乳突区皮肤在质地、色泽、厚度等方面均与面部皮肤最为接近,是一种良好的修复面部皮肤软组织缺损的方法。     

Prefabrication of thin transferable axial-pattern skin flaps: an experimental study in rabbits.

The arteriovenous pedicle of all known axial-pattern skin flaps enters from the deep aspect and consequently the flap must contain fat and/or muscle and be of considerable thickness. In an attempt to fabricate a thinner axial-pattern flap the femoral artery and vein of rabbits were implanted, in various vascular configurations, directly into the subdermal layer of the skin. Implantation was found to provoke an extensive outgrowth of new vessels from the implanted artery and vein, and the progress and pattern of this neovascularisation was studied by carbon gelatine perfusion and histology. Neovascularisation begins within a few days of implantation and progresses rapidly. By 8 to 12 weeks it is possible to elevate regularly a viable, large skin flap based on the implanted pedicle.     

Preconditioning of the distal portion of a rat random-pattern skin flap.

It has been shown that preconditioning either by proximal pedicle clamping or by pedicle intravascular drug administration, for example with adenosine, can improve flap survival. These methods, however, are not well suited to random-pattern flap transfer in the clinical setting. The aim of this study was to evaluate clinically applicable preconditioning methods for random-pattern flaps. Eighteen male Sprague-Dawley rats were used. Bipedicled dorsal skin flaps (2 x 8cm) containing panniculus carnosus were elevated. In the ischaemic preconditioning group the cranial pedicle was clamped for 20min, followed by 40min reperfusion before the cranial pedicle was cut, producing a caudally based random-pattern flap. In the pharmacologic preconditioning group adenosine was locally injected in the cranial half of the flap before the cranial pedicle was cut. In the control group saline was locally injected instead of adenosine and the pedicle was cut in the same manner. Flap survival area was evaluated at day 7. Flap survival area in both preconditioning groups was significantly higher than in the control group (P<0.05). Both preconditioning methods can improve random-pattern flap survival in rats. These methods may prove useful in the clinical setting.     

Effect of clamp versus anastomotic-induced ischemia on critical ischemic time and survival of rat epigastric fasciocutaneous flap

BACKGROUND: There are many models used to explore ischemic-related phenomena. The rat epigastric fasciocutaneous flap model is the one most commonly used. Critical ischemic time is the maximum ischemic insult that tissue can undergo and still remain viable. Experimentally, ischemia is induced either by clamping the vascular pedicle or by dividing the pedicle then performing microvascular arterial and venous anastomosis. We sought to determine what effect the different methods of inducing ischemia have on the critical primary ischemic time and, thus, flap survival. METHODS: A right 3 cm x 6 cm groin flap based on the inferior epigastric vessels was raised in each rat. Ischemic times of 4, 6, 8, or 10 hours were induced either by placing temporary occlusion clamps on each vessel of the vascular pedicle (island pedicle group) or by ligation and division of the pedicle with subsequent microvascular anastomosis (free flap group). Survival was assessed at 7 days. RESULTS: The primary ischemic time at which one half of free flaps are predicted to die was calculated to be 7.60 hours, compared with 6.09 hours for the island pedicle flaps (p<.05). CONCLUSIONS: Fasciocutaneous flaps undergoing ligation and anastomosis are more resistant to ischemia than are those undergoing clamping of the pedicle. Possible etiologic factors responsible for this experimental finding are discussed.