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ORIGINAL ARTICLES
NUMBER 3 YEAR 2005
Study of the Vascularisation of Rectus Abdominis Muscular and Musculo-Cutaneous Flap: Experimental Model in Pig
1 Politraumtology Department, 3rd Surgical Clinic, Clinical Emergency Hospital Timisoara
2 2nd Orthopaedic Clinic, Victor Babes University of Medicine and Pharmacy Timisoara
3 Plastic and Reconstructive Surgical Clinic, Clinical Emergency County Hospital Timisoara
4 Surgical clinic, Timisoara Municipal Hospital
5 Pius Branzeu Center for Laparoscopic Surgery and Microsurgery Timisoara
6 2nd Surgical Clinic, Victor Babes University of Medicine and Pharmacy Timisoara

Correspondence to:
Popescu Mircea Radu, 8 Barbu Iscovescu Str., Apt.7, Timisoara, Romania
Tel.: +40744-624644
Email: ortoal@rdslink.ro

ABSTRACT
This study describes an experimental animal model for the investigation of the vascularization of the rectus abdominis muscle and musculo-cutaneous flap on pig. We used four common breed pigs divided in two groups, one muscular and another musculo-cutaneous, each group contained four flaps, .The flaps were harvested, injected with contrast media and studied by radiological methods. The results consist in creating a protocol for harvesting, preparation and radiological investigation of the vascularization, allowing the visualization of epigastric inferior and superior networks, the connections between them and the fascio-cutaneous perforator vessels. We concluded that the experimental animal model proposed is reproducible and is a useful tool in the experimental researches on flaps vascularization.
INTRODUCTION

Rectus abdominis can be used as muscular or musculo-cutaneous flap, pedicled or free flap, in different sizes or forms, allowing a great amount of clinical applications.1
In one of the biggest prospective multicentric studies the use of free flaps was analyzed by studying a number of 60 variables in 493 free flaps, concluding that when rectus/transverse rectus abdominis muscle flap was used, a lower incidence of postoperative thrombosis was observed.2
Clinical applications are different: breast reconstruction after mastectomy, reconstruction of the thoracic wall, reconstruction of the pharynx or oesophagus, reconstruction after tumoral excision in locally advanced soft tissue sarcomas, reconstructive surgery in head and neck area.3-7 The value of the rectus abdominis flap in different pathological situations of the lower limbs is also well-known.8-10
Despite the knowledge of the vascularization of the skin of the abdomen and the anatomy of the rectus abdominis muscle, the clinical outcome when we use this muscle as a musculo-cutaneous flap cannot always be predicted.11 Further investigations are necessary concerning the anatomy and physiology of the rectus abdominis in an animal model. A series of experimental models for rat, dog, rabbit, and pigwere designed for studying microcirculation and blood flow with radioactive microspheres, dye fluorescence, laser Doppler flowmetry, injection of resins, and India ink.12-16 Studies were performed also on cadavers with Microfil injections and in patients using color Doppler ultrasound.17,18
All these studies suggested the complexity of the microcirculation of the flaps, the lack of information regarding this field and the necessity for further investigations.

MATERIAL AND METHOD

Experimental design
The study involved four common breed pigs weighing between 50 and 56 kg (average = 52 kg), divided in two groups: group 1 with two pigs for harvesting four muscular flaps and group 2 with two pigs for harvesting four musculo-cutaneous flaps. After the flaps were harvested, they were injected with contrast media and were studied by radiology methods.
The results consisted in establishing a protocol for harvesting, preparation and radiological investigation of rectus abdominis muscle in pig, which allows us to create an experimental model for the study of vascularization using contrast media.

Operative technique
The animals were preanesthetized with Thiopental (5 mg/kg bw i.v.) and Listenol (2 mg/kg bw i.v.); then were intubated and anesthetized with Halotan 0.6-2% and Esmeron (5 mg/kg bw i.v. bolus and after 60 minutes 2 mg/kg bw at every hour).
For harvesting the muscular flap we started by median xifo-suprapubic incision, followed by dissection of fascio-cutaneous perforators and cutting of these vessels after coagulation. The dissection of anterior sheet was performed starting at the median side to the lateral part of muscle and cranio-caudal. During this dissection we isolated the two groups of perforating vessels - medial and lateral. The posterior dissection was started in caudal part of the muscle where we found the inferior vascular pedicle which emerges from epigastric caudalis artery, branch of pudendal epigastricus trunk (this trunk is formed by tree vessels: epigastric caudalis artery, epigastric caudalis superficialis artery and pudenda externa artery). Next we detached the rectus abdominis from the peritoneum by dissecting posterior from the posterior sheet and coagulating and cutting the posterior perforator vessels (those vessels emerge from abdominalis cranialis artery, branch of aorta abdominalis artery).
Fig. 1. Rectus abdominis muscular flap (in left side of figure) and musculocutaneous flap (in right side of figure) after complete harvesting a [...]
We found during the posterior dissection in the cranial part of muscle the main proximal pedicle - epigastric cranialis artery - terminal branch of toracica interna artery. Also, during the proximal dissection we founded in every case superficial superior epigastric pedicle who emerge from thoracic externa artery (branch of axilar artery) and an anastomotic branch from epigastric cranialis artery. Finally, we dissected and isolated the main vascular pedicles, inferior and superior epigastric pedicles, and, after clamping, we revealed the entire flap.
For harvesting the musculo-cutaneous flap we followed the same procedure as before, except that we did not dissect on the anterior surface of the muscle, but we harvested the muscle together with the superjacent skin territory.(Fig 1)
We have catheterized the superior epigastric artery (i.v. cannula with P.T.F.E. radioopaque catheter & injection valve G x Øx L 20 x 1.1 x 33mm Mediflon manufactured by Eastern Medikit Ltd.India) and washed it with 40 ml Ringer lactate solution with heparin (500 UI heparin/ml), followed by 20 ml Xylonest 0.25% solution (Astra Chemicals GmbH, Germany) and 20 ml NaCl 9%0 solution. We clamped the inferior epigastric pedicle, ligatured the superior epigastric veins and injected 20 ml Ringer lactate solution with heparin. We transported the flaps covered in dress moistened with NaCl 9%0 solution to the radiology investigation room. We have declamped the inferior epigastric pedicle, washed it with 20 ml Ringer lactate solution with heparin and after that we injected contrast media (Omnipaque 350mg I/ml - Nycomed Imaging AS, Norway) through the catheterized superior epigastric artery, at the same time with continue X ray exposure. Next we made standard plain X rays of the flaps in A-P and lateral views.(Fig 2,Fig 3)
Fig. 2. Radiological lateral view of musculocutaneous free flap.
Fig. 3. Radiological A-P view of muscular free flap.

RESULTS

Due to this preparation protocol before administration of contrast media, it was possible to visualize the entire vascular network of the flap from the proximal end of the superior epigastric artery to the distal end of the inferior epigastric artery. Despite the fact that we did not have any previous experience with a vasodilatatory substance, we have started our tests with administration of Xylonest 0.25% solution, because we thought that this agent will diminish the vasospasm and will improve the penetration of contrast media through the vascular system.
We harvested eight flaps: four muscular flaps and four musculo-cutaneous flaps. The mean harvesting time was 120 minutes for the muscular flap and 90 minutes for the musculo-cutaneous flap. In each of these flaps, we accomplished studies of the vascular network and of the connections between superior epigastric system and inferior epigastric system by radiological means: we continued to expose every flap to X rays and we followed up and recorded the dynamic course of the contrast flow from the RxTv monitor. On musculo-cutaneous flaps, it was also possible to visualize the fascio-cutaneous perforator vessels.
Thus, it was possible to create and test an experimental model for the study of the vascularization of muscular and musculo-cutaneous flap of rectus abdominis in pig.



DISCUSSION

According to the clinical studies regarding the muscular and musculo-cutaneous flaps, the functionality of the vascular network is of paramount importance in the outcome of the free flap.1-19 Hallock G.G. et al. used laser Doppler flowmetry to study TRAM and DIEP flaps in a rat model and found that relative flow to these rat ventral abdomen models was directly proportional to the number of retained musculocutaneous perforators, but a single perforator only could routinely allow near-total survival.13 Calfee EF 3rd et al. have used angiography to confirm vascular patency of rectus abdominis free flaps in dogs.14 Morris SF, in his study regarding the possibilities to predict the survival of experimental skin flaps prior to their elevation in guinea pigs and rabbits, have used fluorescein dye injection to assess viability of the flaps and whole-body fresh cadaver lead oxide injections to provide cutaneous angiograms. The results of the study reinforce the angiosome concept.15 Thomson JG used radioactive microsphere technique for measuring the blood flow after flap elevation in pig model in his experimental study regarding the fasciocutaneous and skin flaps.16 Lorenzetti used color Doppler ultrasound to measure the blood flow in the donor and recipient arteries as well as in the deep superior epigastric artery of 10 patients having free transverse rectus abdominis myocutaneous (TRAM) flaps. Using this method he was able to measure the peak, minimum and mean velocities, the diameter of the vessel, and the resistance index of both the deep superior and inferior epigastric arteries and thoracodorsal arteries. He found that blood flow increased in the superior epigastic artery on the donor side after free TRAM transfer as expected (indicating the delay phenomenon), but harvesting the flap did not affect the circulation in the opposite rectus abdominis muscle. The inferior epigastric arterial system was dominant in all patients.17 Blondeel PN used anatomical studies with Microfil injections of the superficial venous system of the DIEP or TRAM flap in 15 cadaver and 3 abdominoplasty specimens. His conclusion was that large lateral branches crossing the midline were found in only 18 percent of cases, whereas 45 percent had indirect connections through a deeper network of smaller veins and 36 percent had no demonstrable crossing branches at all. This absence of crossing branches in many patients may explain why survival of the zone IV portion of such flaps is so variable and unpredictable.18
From anatomic point of view, the pig is an experimental animal with very similar structure compared to human, thus studies performed on experimental models on this animal allow obtaining results that have a good correlation with phenomena meet in clinical human practice.20,21 Physiological and anatomical similarities between man and pig made this animal a good model for man in many research areas such as wound healing, coronary diseases and also pharmacological and toxicological research.22-24
In human, the arterial vascularization of rectus abdominis muscle is realized by the superior epigastric artery (branch of internal mammary artery at the level of the seventh rib) and the inferior epigastric artery (branch of external iliac artery). Inferior epigastric artery has its course between the muscle and the posterior wall of the sheath and at the level of the umbilicus divides into several vessels that anastomose with the superior epigastric artery. There are also anastomoses between the terminal branches of the 4 or 5 lower posterior intercostal arteries and the lumbar arteries and the inferior epigastric artery.25
With this study we intended to develop and to standardize an experimental model for the study of the muscular and fascio-cutaneous vascularization in pig by dissecting and than visualizing the vessels using contrast agents.
The use of contrast agent and the continuous X-ray exposure allow us to demonstrate and study the connections between the superior epigastric artery network and the inferior epigastric artery network and the fascio-cutaneous perforator vessels.
The results were stored in digital format by video recording from TV monitor of the X ray unit and as pictures from plain X rays.
With this study, we intended to develop and standardize an experimental animal model for the investigation of the vascularization of the rectus abdominis muscle and its superjacent skin territory.

CONCLUSIONS

Because until now, the data from the literature regarding this subject are scarce, our results can contribute to further investigations regarding vascularization of muscular flaps.
The connections between the superior epigastric artery network and the inferior epigastric artery network and the fascio-cutaneous perforator vessels are better demonstrated by using contrast agent and the continuous X-ray exposure.
The experimental animal model proposed is reproducible and is a useful tool for the experimental researches on flaps vascularization.

REFERENCES

1. Sinsel NK, Guelinckx PJ. Peculiar indications of free rectus abdominis flap in reconstructive surgery. A review of our experience. Acta Chir Belg 1995;95(6):289-96.
2. Khouri RK, Cooley BC, Kunselman AR, et al. A prospective study of microvascular free-flap surgery and outcome. Plast Reconstr Surg 1998;102(3):711-21.
3. Schusterman MA. The free TRAM flap. Clin Plast Surg1998;25(2):191-5.
4. Tukiainen E, Popov P, Asko-Seljavaara S. Microvascular reconstructions of full-thickness oncological chest wall defects. Ann Surg 2003;238(6):794-801.
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6. Bonvalot S, Kolb F, Mamlouk K, et al. Free-flap reconstruction of locally advanced soft tissue sarcomas. Ann Chir 2001;126(4):308-13.
7. Schipper J, Klenzner T, Arapakis I, et al. The transverse rectus abdominis muscle island flap as a second defensive line in microvascular reconstruction of defects in the head and neck area. HNO 2005; Jun 10, Epub ahead of print.
8. Ionac M, Rus L, Papurica M, et al. Primary free flap closure of the injuries of the lower extremity. Romanian Journal of Hand and Reconstructive Microsurgery 2002; 7(1-2):33.
9. Geishauser M, Staudenmaier R, Groner R, et al. Free microvascular rectus abdominis muscle flap for soft tissue reconstruction of the lower leg and foot: results and donor site defect. Handchir Mikrochir Plast Chir 1999;31(1):21-6.
10. Kuokkanen HO, Tukiainen EJ, Asko-Seljavaara S. Radical excision and reconstruction of chronic tibial osteomyelitis with microvascular muscle flap. Orthopedics 2002;25(2):137-40.
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13. Hallock GG, Geoffrey G, Rice DC. Comparison of TRAM and DIEP flap physiology in a rat model. Ann Plast Surg 2004;114(5):1179-84.
14. Calfee EF 3rd, Lanz OI, Degner DA et al. Microvascular free tissue transfer of the rectus abdominis muscle in dogs. Vet Surg 2002;31(1):32-43.
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16. Thomson JG, Kerrigan CL. Fasciocutaneous flaps: an experimental model in the pig. Plast Reconstr Surg 1989;83(1):110-7.
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18. Lorenzetti F, Ahovuo J, Suominen S, et al. Colour Doppler ultrasound evaluation of hemodynamic changes in free tram flaps and their donor sites. Scand J Plast Reconstr Surg Hand Surg 2002;36(4):202-6.
19. Erni D, Harder YD. The dissection of the rectus abdominis myicutaneous flap with complete preservation of the anterior rectus sheath. Br J Plast Surg 2003;56(4):395-400.
20. Kerrigan CL, Yelt RG, Thomson JG, et al. The pig as an experimental animal in plastic surgery research for the study of skin flaps, myocutaneous flaps and fasciocutaneous flaps. Lab Anim Sci 1986;36(4):408-12.
21. Ionac M, Avram A., Dindelegan G, et al. The pig as an animal model in training and research of free flaps. Romanian Journal of Hand and Reconstructive Microsurgery 2002;7(1-2) :34.
22. Davidson JM. Experimental animal wound models. Wounds 2001;13(1):9-23.
23. Bayes-Genis AC, Kantor BC, Keelan PC, et al. Restenosis and hyperplasia: animal models. Current Interventional Cardiology Reports 2000;2:303-8.
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25. Sinelnikov RD. The arteries of the pelvis, in Atlas of Human Anatomy, vol II, Moscow: Mir Publishers, 1989, p. 321.



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