This paper describes the steps required to raise a fasciocutaneous epigastric free flap and transfer it to the neck in the rat.
Free tissue transfer has been increasingly used in clinical practice since the 1970s, allowing reconstruction of complex and otherwise untreatable defects resulting from tumor extirpation, trauma, infections, malformations or burns. Free flaps are particularly useful for reconstructing highly complex anatomical regions, like those of the head and neck, the hand, the foot and the perineum. Moreover, basic and translational research in the area of free tissue transfer is of great clinical potential. Notwithstanding, surgical trainees and researchers are frequently deterred from using microsurgical models of tissue transfer, due to lack of information regarding the technical aspects involved in the operative procedures. The aim of this paper is to present the steps required to transfer a fasciocutaneous epigastric free flap to the neck in the rat.
This flap is based on the superficial epigastric artery and vein, which originates from and drain into the femoral artery and vein, respectively. On average the caliber of the superficial epigastric vein is 0.6 to 0.8 mm, contrasting with the 0.3 to 0.5 mm of the superficial epigastric artery. Histologically, the flap is a composite block of tissues, containing skin (epidermis and dermis), a layer of fat tissue (panniculus adiposus), a layer of striated muscle (panniculus carnosus), and a layer of loose areolar tissue.
Succinctly, the epigastric flap is raised on its pedicle vessels that are then anastomosed to the external jugular vein and to the carotid artery on the ventral surface of the rat’s neck. According to our experience, this model guarantees the complete survival of approximately 70 to 80% of epigastric flaps transferred to the neck region. The flap can be evaluated whenever needed by visual inspection. Hence, the authors believe this is a good experimental model for microsurgical research and training.
游离组织移植在临床实践中越来越多地用于自20世纪70年代重建1-5缺少组织。这使得从摘除肿瘤,外伤,感染,畸形或烧伤1-7造成复杂,否则无法治愈的缺陷重建。这种自由折翼是用于重构高度复杂的解剖区域,如那些在头部和颈部,手,脚的,和会阴1,4-特别有用。
然而,即使在今天的外科研修生经常受到的参与提高,传输和insetting一个游离皮瓣与利用显微外科技术和仪器8,9几个步骤的复杂性吓倒。此外,它已被广泛接受,要成为一个精通microsurgeon,在动物模型中广泛的实验的做法是强制4,8-13。
此外,基础和转化研究在自由组织转移的面积是重要的临床潜力8,14-16。尽管如此,研究人员经常利用组织移植显微车型由于对参与手术方案4,8-14技术方面缺乏信息却步。鼠是显微研究和培训一个很好的动物模型,因为它是相对便宜,容易保存,并且适合频繁操作8,11,13,14,17,18。
虽然几个自由骨骼,肌肉和皮肤护翼已在大鼠18-24了说明,但游离胃脘皮瓣是最广泛使用的用于教学目的9,12,13,18,25。该游离皮瓣最早是在1967年由蟾蜍和Murray描述,并从此得到了越来越多的人气,由于多种因素,即不变血管解剖,相对容易清扫,相当大的营养血管和皮肤的冗余供体区,WHICH允许从瓣的高度4,9-11,13,17,18,25-28造成的缺陷缝合。
皮瓣解剖学和组织学
胃脘皮瓣由腹壁浅动脉和静脉( 图1)提供。这些船只发源于分别排入股动脉和静脉。上平均的腹壁浅静脉的口径为0.6〜0.8毫米,0.3到0.5毫米腹壁浅动脉的对比( 图2)17,18。浅腹壁下动脉散发出的两个主要分支:横向和内侧支,反过来分裂多次,这源于供应的大部分地区上腹部的体壁的毛细血管网络。这些毛细管流入具有平行当然到动脉树( 图2)13,17,18的腹壁浅静脉的支流。 图3重图通过介绍可以在腹部皮瓣进行动员腹壁浅血管供应腹外侧腹壁的区域。此翼片可高达5厘米长3厘米,宽13,17,18。
组织学上,翼片由覆盖所述腹腹壁肌肉( 图4)13,17,18外皮的。它含有皮肤的表面层,由真皮和表皮形成。下方的皮肤有一个名为脂膜adiposus脂肪组织层。下面这一层有称为肉膜 18,28,29横纹肌另一层。下面的肉膜有松动乳晕组织是肤浅覆盖更大的腹部肌肉的深筋膜。因此,护翼是组织的复合块,包含所有这些层,除了深肌肉筋膜( 图5)13,17,18,27-31。
The most important aspect to obtain consistent flap survival is paying attention to detail in various steps of the microsurgical technique. For example, to obtain good visualization of the vessels, of the surgical instruments and of the fine suture lines, it is very helpful to place underneath the vessels, a sterilized colored plastic background. As many researchers, we prefer to use sterilized fragments of yellow or green balloons (Figures 7 and 11). This background provides the additional advantage of minimizing adherence of suture lines to the adjacent structures, which sometimes leads to the need of pulling the suture line with too much tension, which may in turn lead to vascular tearing. Finally, the use of a background has the additional advantage of decreasing the probability of inadvertently dragging potential thrombogenic tissue debris to the anastomosis site.
Considering that the flap’s vessels are very fine and fragile, it is important not to pinch the entire width of the vessels, in order to avoid intimal lesion that, in turn, will lead to intravascular thrombosis and flap failure. To prevent inadvertent injury to both the flap’s vessels and to the recipient site’s vessels, it is safer to liberally ligate and divide neighboring tributaries, which will allow an easier manipulation of these vessels.
Before starting the anastomoses, it is vital to place the vessels in their definitive position, striving to prevent vascular kinking or torsion of the flap’s pedicle. Given the small caliber and delicate consistency of the vessels, these are often difficult to exclude unequivocally. One helpful trick is to secure the flap in its final position with 3 stitches placed away from the site of the anastomoses. Next, if in doubt, temporarily open the vascular clamps placed at the flap’s pedicle, and fill the vessels’ lumen with heparinized normal saline in a concentration of 10 IU/mL until they become engorged. This leads vessels to assume the configuration they will present after being perfused by blood, as when the clamps are removed after anastomoses completion.
Moreover, it is of paramount importance to detect any air bubbles, even if small, inside the vessels during the entire procedure and particularly before tying the final stitches. If these bubbles are distant from the vascular section, the vessels can be milked gently with microsurgical forceps. If they are located close to the anastomotic sites, simple irrigation leads the less dense bubbles to be easily expelled from the vascular lumen. Failure to acknowledge the presence of air bubbles can cause irreversible flap ischemia and necrosis, no doubt due to the fine caliber of the flap vessels.
Additionally, it cannot be overemphasized the need for meticulous care while passing and tying the stitches, in order to: include the three layers of the vessels (intima, media and adventitia); obtain good vessel eversion to ensure adequate intimal contact, which is vital to anastomosis sealing and endothelial regrowth; avoid loose vascular contact, which will result in anastomotic incompetence, i.e., bleeding; and avoid grabbing too much vascular tissue, which will lead to anastomosis stenosis and proclivity to thrombosis, which in turn will result in venous congestion or poor flap perfusion, if the vein or artery are involved, respectively.
Finally, it is essential to ensure perfect hemostasis, during the entire procedure, especially when raising the flap in its deep surface. Otherwise hematoma formation and rat death are likely to ensue.
Modifications and troubleshooting of the technique
The authors observed that making a transverse incision in the middle portion of the SCM using an electric cautery, not only allows a better exposure of the carotid artery, but also minimizes the risk of undue tension over the future arterial anastomosis.
Another important technical tip is to start the anastomosis from the vessels’ back wall, in order to minimize the risk of unwillingly catching this wall when placing the stitches in the more easily exposed front wall. If the back wall is sutured to the anterior aspect of the anastomosis, lack of vascular patency will almost invariably result either immediately due to mechanical reasons or after only a few hours as a result of thrombosis8.
If the anastomoses of the epigastric vessels of the rat are considered too technically challenging due to the small caliber of these vessels, the femoral vessels can be ligated distal to the origin of the epigastric vessels and used as the vascular pedicle of the epigastric flap. In this way, larger vessels will be used (the femoral artery has a caliber of 1.0 to 1.2 mm; and the femoral vein has a caliber of 1.2 to 1.5 mm). Moreover, by dissecting and ligating the other tributaries of the femoral vessels, a vascular pedicle length of over 2 cm can be obtained, which will facilitate flap insetting18,34,35.
Reproducibility
Our experience of more than ten years of using this flap for teaching and research purposes strongly suggests that the rat epigastric flap is a reproducible model of free tissue transfer11,13,17,18,26. It can be easily incorporated in microsurgical courses, as it is a good teaching and training model for microsurgery trainees11,13,17,18,26. In our experience, although technically challenging in the beginning for the novice in microsurgery, after some training, the free epigastric flap can be successfully transferred to the neck of the rat with minimal to no subsequent necrosis in 70 to 80% of cases. These results concur with those generally reported in the literature13,18,36.
Significance with respect to existing methods
Numerous free flaps have been described in the rat10,16,18,37-39. The most commonly used for teaching and research purposes have been the transverse rectus abdominis myocutaneous flap, the latissimus dorsi and serratus anterior muscle flaps, the hind limb replantation model, and the epigastric (groin) flap18,35. These flaps have been favored, due to their consistent anatomy and sizeable vascular pedicle. The epigastric flap is arguably the one associated with lesser donor site morbidity, as it dissected above the muscle fascia18. Moreover, the epigastric flap, described in 1967, was the first flap to be described in rats34,35. This occurred only 4 years after the first description of an experimental flap in an animal by Goldwyn. Interestingly, this flap was a groin flap in the dog34.
Limitations of the technique
The two main limitations of this model are the need for microsurgical skills in order to carry out the surgery, and the presence of significant necrosis in 20 to 25% of cases, according to different authors13,18,36. Another potential limitation of the model herein presented is the auto cannibalism of the flap. However, as the authors above, this is an infrequent finding that almost only occurs in cases of total flap necrosis.
Future applications of the technique
The rat epigastric free flap can be used in experimental studies of tissue perfusion, tissue repair and surgical wound infection40,41. Its nutrient vessels are particularly suitable for intravascular injection of solutions containing substances of interest, namely drugs, viral vectors or liposomes, that will mostly produce a local or regional effect30,31. In addition, beneath the flap, pathogens, foreign bodies, radioactive seeds or chemicals can also be placed, mimicking several disease processes and potential treatments30,31.
The authors have nothing to disclose.
作者之一(迪奥戈卡萨尔)收到的资助从程序的高级医学教育,这是由FundaçãoCalouste Gulbenkian博物馆,FundaçãoChampalimaud,DA部:ËSAUDE对Fundação一个西恩西亚ËTECNOLOGIA,葡萄牙赞助。
笔者想感谢阿尔贝托·塞韦里诺先生的技术帮助,在拍摄和编辑视频。作者也感谢奥克塔维奥Chaveiro先生,马可·科斯塔先生和卡洛斯·洛佩斯先生为筹备在本文所提出的动物标本帮助。
最后,作者要感谢Gracinda梅内塞斯女士的帮助,所有与动物的采集和维护的后勤方面。
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