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.
自由組織移動はますます1970 1~5ので欠落組織を再構築するために臨床で使用されてきました。これは、腫瘍摘出、外傷、感染症、奇形や火傷1-7から得られた複合体とそれ以外の治療不可能な欠陥の再構築を可能にしました。この種の無料フラップは頭や首、手、足、および会陰1,4のものと同様、非常に複雑な解剖学的領域を再構築するために特に有用です。
しかし、今日でも外科的研修生は頻繁に顕微技術と機器8,9を使用して自由なフラップを上げ転送しinsettingに関与するいくつかの手順の複雑さによってひるむされています。また、それは広く堪能マイクロ手術の専門医になるためにことが認められている、動物モデルにおいて豊富な実験実習は4,8-13必須です。
また、基本とトランスレーショナルリサーチ無料組織転送の領域に大きな臨床的可能性8,14-16です。それにもかかわらず、研究者が頻繁術4,8-14に関わる技術的側面に関する情報が不足しているため、組織の転送の顕微モデルを使用してから抑止されています。それは比較的、安価で維持しやすく、かつ頻繁な操作8,11,13,14,17,18を受け入れられるように、ラットは、顕微研究と訓練のための優れた動物モデルです。
いくつかの無料の骨、筋肉と皮膚フラップラット18-24に記載されているが、自由な心窩部筋膜皮弁は教育目的9,12,13,18,25のために最も広く使用されています。この無料のフラップはWH、最初Strauchとマレーによって1967年に記述され、いくつかの要因、すなわち一定の血管解剖、解剖の相対的な容易さ、かなりの栄養血管、およびドナーゾーンの皮膚の冗長性に、それ以来増加し人気を得ていますICHは、フラップの標高4,9-11,13,17,18,25-28に起因する欠陥の主要な閉鎖を可能にします。
フラップ解剖学と組織学
上腹部フラップは浅腹壁動脈と静脈( 図1)によって供給されています。これらの血管は、それぞれに由来し、大腿動脈と静脈に排出します。平均的に浅腹壁静脈の口径は、浅腹壁動脈( 図2)17,18の0.3〜0.5ミリメートルと対照的な、0.6〜0.8mmです。心窩部の外皮のほとんどを供給毛細血管ネットワークを発信、横方向と順番に複数回分割内側枝:浅腹壁動脈は、2つの主要な枝を放ちます。これらの毛細血管は、動脈樹( 図2)13,17,18と平行のコースを持っている浅腹壁静脈の支流に排出します。 図3の再のダイアグラム上腹部のフラップに動員することができ浅上腹部管により供給された腹腹壁の領域を示しています。このフラップは、長さ5cm、幅13,17,18の3センチまで可能です。
組織学的には、フラップは腹外側腹壁の筋肉( 図4)13,17,18 をカバー外皮で構成されています。これは、真皮と表皮によって形成された皮膚の表面層を、含まれています。皮膚の下に脂肪の皮筋層という名前の脂肪組織の層が存在します。この層の下に皮筋層 18,28,29として知られる横紋筋の別の層が存在します。 皮筋層の下には、より大きな腹部の筋肉をカバーし、深い筋膜に表面的であるゆるい疎性結合組織があります。したがって、フラップは( 図5)1深部筋膜を除いて、すべてのこれらの層を含む、組織の複合ブロックであります3,17,18,27-31。
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.
著者の一人(ディオゴカザル)は、電子Tecnologia、ポルトガル電子FundaçãoパラACiênciaMINISTERIOダSaúde、Fundaçãoカルースト・グルベンキアン、Fundaçãoシャンパリモーが主催している高度な医学教育のためのプログラムからの助成金を受けました。
著者らは、ビデオを撮影し、編集中の氏アルベルト・セヴェリーノの技術的なサポートに感謝したいと思います。著者らはまた、本論文で動物の標本を調製する際に彼らの助けのための氏オクタビオChaveiro氏、マルコ・コスタ氏とカルロス・ロペスに感謝しています。
最後に、著者らは、動物の獲得と維持に関連するすべての物流の面で彼女の助けのために氏Gracindaメネゼスに感謝したいと思います。
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