Yuji Inada, Toshiyuki Hirai, Akihiro Fukui, Shohei Omokawa, Yoshio Mii, and Susumu Tamai

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VENOUS FLAP: INVESTIGATION OF THE WIDTH AND AREA OF SURVIVAL WITH ONE FLOWTHROUGH VEIN PRESERVED ABSTRACT A quantitative analysis was undertaken to investigate the width and area of survival of flow-through venous flaps in 20 ears of 10 rabbits. The 3.0- x 3.0-cm flap models, which included one flow-through vein, were prepared with additional circulation from the graft bed and surrounding tissue excluded, as far as possible. The flaps were divided as follows: Group A—composite grafts (n = 10), and Group B—flowthrough venous flaps (n = 10). All flaps in Group A became necrotic and all those in Group B showed partial survival along the flow-through vein. The average survival width was 1.10 ± 0.48 cm, and the survival rate was 44 ± 19.3 percent. Microangiograms revealed patency of the flow-through vein in all flaps of Group B. Histologically, there tended to be progressively more fibrous tissue in the area further away from the flowthrough vein. The model is useful to investigate the width and area of survival in flow-through venous flaps.

We have shown that the flow-through venous flap can survive in a recipient bed with poor blood supply, using rabbit-ear skin-flap models. 12 There are, however, many questions remaining to be answered about the mechanisms of survival, and it is no exaggeration to state that an investigation of this field has just begun. The aim of this study was to carry out quantitative analyses of the width and area of flap survival, using only one flow-through vein as a pedicle, and excluding blood flow from the graft bed and surrounding tissue, as much as possible.

MATERIALS AND METHODS A total of 20 ears from 10 rabbits, weighing 3 kg on average, were used. The experiment was conducted under GOF mask inhalation anesthesia. After the ear had been disinfected and shaved thoroughly, a 3.0 x 3.0 cm flow-through venous flap was designed, with the flap including only one vein running through the outside margin of the dorsum of the auricle, so as to place the vein at the outside margin of the flap and not

Departments of Orthopedic Surgery, Nara Medical University, Nara, Japan and Omiwa Hospital, Sakurai, Japan Reprint requests: (until September, 1992): Dr. Inada, Orthopedic Research, Rm. 314, Hospital forSpecial Surgery, 535 E. 70th St., New York, NY 10021 After that date: Dr. Inada, Dept. of Orthopedic Surgery, Nara Medical University, Shi jyocho 840, Kashihara, Nara 634, Japan Accepted for publication January 2, 1992 Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.

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DESIGN OF EXPERIMENTAL MODEL »*

Figure 1. A, A s q u a r e flow-through venous flap ( 3 x 3 cm) with a single flow-through vein. B, The back of the flowthrough venous flap. E x p a n d e d venous branches are s e e n .

to involve the central neurovascular bundles (Fig. 1A). At this site, only minimal venous variation occurs, and a flow-through venous flap model without a distinct named artery can be constructed. The flap was raised at the level of the perichondrium on bare cartilage, to avoid injuring the venous network (Fig. IB), and then sutured back into its original position with 4-0 nylon. We confirmed that the flap had no other vessel communication, excepting the one vein, by dissecting the vein using microsurgical technique and the operating microscope. In order to exclude the influence of additional blood flow around the flap, a central artery was isolated from the flap as much as possible, with dissection carried out under the operating microscope at the base of the auricle proximally and at a distance from the flap distally, to avoid injuring the vein and concomitant nerve; the artery was then ligated. The experimental flap models were divided into two groups (Fig. 2): Group A—controls; composite grafts, i.e., free skin grafts with flow-through veins ligated (n = 10); and Group B—flow-through venous flaps preserving one flow-through vein (n = 10). After each flap was elevated, it was irrigated in saline solution with antibiotics and received a subinjection of 1 percent Xylocaine to avoid vasospasm. For each flap in the two groups, survival was ascertained 14 days after the operation by macroscopic, microangiographic, and histologic observations. After inhalation anesthesia using halothane, both the carotids were exposed, a 24G Teflon tube was inserted into them distally to perfuse sufficient heparin sodium into the ear, and 20 percent Micropaque with 5 percent gelatin was injected. Subsequently, the ear was resected en bloc, preserved by freezing for 30 min, and soft x-rays were taken. After microangiography, the ear was fixed in a 10 percent formalin solution for three days, and the flaps were dissected and stained with 298 hematoxylin and eosin.

B

Group A

Group B

'flow-through" Venous Flap

Composite Graft

Figure 2. Experimental groups.

RESULTS In Group A, all 10 flaps suffered complete necrosis (Fig. 3A). No survival due to circulation from the surrounding tissue was found at the edge of the flap. Microangiograms revealed avascularization (Fig. 3B), and complete necrosis was shown histologically (Fig. 3C). In Group B, all 10 flaps presented partial survival along the flow-through vein, although hair ingrowth was poor. Macroscopically, there were visible characteristic changes. Flap color was pale immediately after elevation; delayed edema appeared five to seven days after operation (Fig. 4A); and necrotic sites became increasingly clear two weeks after flap elevation (Fig. 4B). The width of the part surviving for a week dimin-

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Venous Rap(3x3cm)

B

Figure 3. A, Macroscopic findings in Group A. All flaps showed complete necrosis at two weeks after operation. B, Microangiogram in Group A revealed avascularity. C, Histologic findings in Group A showed complete necrosis.

ished after two weeks. Survival widths ranged from 3 mm to 20 mm, and the average of the maximum and minimum distance from the flow-through vein (Fig. 4C) was 1.10 ± 0.48 cm, with a range of 0.5 cm to 1.75 cm (Table 1). The average rate of the survival areas was 44 ± 19.3 percent, with a range of 22 to 70 percent (Table 2).

In the microangiograms, all preserved flow-through veins were patent, and venous branches expanding from the flow-through vein were observed. Blood vessels anastomosed to the surrounding tissue at the upper and lower margins of the flap were found, but those at the side of the central artery were scarcely visible, even at two weeks after operation (Fig. 4D).

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Figure 4. A, Macroscopic finding in Group B. The flow-through venous flap showed slight edema at one week after operation. B, Macroscopic finding in Group B. The flow-through venous flap survived along the flow-through vein, although hair ingrowth was poor. C, Measurement method of the survival width. D, Microangiogram in Group B. All preserved veins were patent and venous branches expanding from the flow-through vein were observed. E, Histologic findings in Group B (x40, transverse plane in a flow-through venous flap). A representative case; normal skin structure is preserved near the flow-through vein, while a tendency toward fibrosis became more noticeable in the area further away from the vein; finally, necrosis is observed.

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in many clinical cases, while different survival rates have been reported. Honda5 first applied flow-through venous flaps, 15 D(cm) x 20 mm to 30 to 40 mm in size (width: 15 to 30 mm), Group A Group B Case including one flow-through vein as a pedicle in clinical 1.25 1 0 cases. The result was that two of five cases survived 2 0 1.65 completely and the other three became partially ne0 3 0.50 4 0 1.20 crotic. Tsai,6 however, reported that 11 flaps, up to 0 5 1.00 50 mm in width, survived completely on the dorsum 6 0 1.65 of the finger, by anastomosing several veins. We have 7 0 0.80 also demonstrated that flaps with plural flow-through 8 0 0.70 veins, 15 mm to 20 mm in width, had complete sur0 9 1.75 10 0 0.50 vival.7 As for the largest flap, Fukui et a!.8 reported that 0 Avg. ± SD .10 ± 0.48 a flap, 60 mm in length and width, including three flowthrough veins, survived with only superficial necrosis on the dorsum of the hand. From the reported clinical results, we can deduce Table 2. Experimental Results of Measurements that the range in which a flap can survive with only one for Survival Areas of Flow-Through Venous Flaps flow-through vein is under 1 to 2 cm in width. Clinically, Survival Rate however, the condition of the graft bed, the donor site Flap Area Survival Area Case (cm*) (cm2) (%) of the venous flap, and the circulation around the flap 1 51 7.00 3.55 varied, and it was not ascertained whether the anasto2 66 7.50 4.95 mosed veins were patent. Since the flaps were small 3 22 1.35 6.25 and most of them were grafted on the finger, which had 50 4 4.00 8.10 a comparatively good blood supply, we conclude that 5 3.00 40 7.50 6 66 reported survival was due to the circulation from sur4.62 7.00 29 7 2.24 7.84 rounding tissue. 24 8 2.03 8.41 The purpose of our study was to investigate the 70 9 6.25 4.38 width and area of survival of flow-through venous flaps 22 10 1.50 6.90 with only one flow-through vein as a pedicle, excluding Avg. ± SD 44 ± 19.3 circulation from the graft bed and from surrounding tissue, as far as possible. In control Group A, complete necrosis occurred and no survival was observed at the Histologically, collagen fiber in the subdermal layer edge of the flap, even from surrounding circulation, in presented a normal skin structural appearance near all 10 cases. Microangiograms did not reveal much the flow-through vein, while increasing fibrosis was neovascularization in the surrounding tissue. In Group noted in the area more distant from the flow-through B, the flaps survived along the flow-through vein. The vein, and, finally, necrosis was evident (Fig. 4E). Hair average of survival widths was 1.10 ± 0.48 cm and the ingrowth remained poor in these flaps. average percentage of survival areas was 44 ± 19.3 percent. Microangiograms revealed patency of the preserved flow-through vein in all surviving flaps, and DISCUSSION almost no anastomosed vessels from the side of the central artery. Histologically, a strong tendency toward Our studies have demonstrated the survival of the fibrosis of collagen fiber was observed in the area flow-through venous flap in the rabbit ear, which was furthest away from the preserved flow-through vein. grafted onto cartilage with poor blood circulation.12 This seems to validate the fact that most flaps survived We believe that the distribution of the venous network because of venous blood spreading from the one flowin the flap is a significant factor in flap survival. It through vein. is also necessary that the ear vein, when acting as a However, survival widths and areas were inconsispedicle, should have arterial rather than venous char- tent. We suggest that this was influenced by the acteristics, i.e., good venous pressure and high venous amount of blood flow in the subcutaneous vein, a oxygen tension.3 However, it has also been reported capacity vessel, as a pedicle is easily influenced by that the measurement of blood flow in the flow- the local or general effects of surgery and anesthesia. through venous flap is not possible just after surgery,4 It may be unreasonable to expect consistent data when and no studies have been done on what size flap can using a vein as a pedicle. survive with only one flow-through vein. Spindly and As for the reasons for survival of flow-through thin flaps have been raised on a single venous pedicle venous flaps, Baek9 reported that saphenous veins as

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Table 1. Experimental Results of Measurements for Survival Widths of Flow-Through Venous Flaps

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At present, we are performing quantitative analypedicles of saphenous venous flaps in the dog, had 1.5 to 5 mmHg venous pressure, which seemed to effect a ses, comparing cases of surrounding tissue with good "false" circulation of venous blood. Although our ex- blood supply and with poor blood supply, as a prelimiperimental models were different from Baek's, we re- nary step, and we will report our results in the near ported that the veins of flow-through venous flaps in future. the rabbit ear had 2.2 ± 0.42 mmHg venous pressure and clinically, veins from the dorsum of the finger to the dorsum of the hand, (which was selected as the REFERENCES recipient site) had venous pressures two to three times higher than rabbit-ear veins (venous pressure of the 1. Fukui A, Inada Y, Tamai S, et al: Skin graft including subcutadorsum of the finger-, afferent venous pressure 5.9 ± neous vein; Experimental study and clinical applications. I Reconstr Microsurg 4:223, 1988 2.4 mmHg; efferent venous pressure 2.9 ± 1.0 mmHg).3 2. Inada Y, Fukui A, Tamai S, Masuhara K: Experimental studies of From this, we deduce that a dense venous network skin flaps with subcutaneous veins. J Reconstr Microsurg 5: alone will allow a flow-through venous flap, more than 249, 1989 3. Inada Y, Fukui A, Tamai S, et al: An experimental study of the 1.10 ± 0.48 cm in width (the value validated experimenvenous flap; Investigation of the recipient vein. ) Reconstr tally) to survive in clinical cases. In any case, it is Microsurg 6:123, 1990 significant that the survival width and area of the flow4. Sasa M, Xian W, Breidenbach W, et al: Survival and blood flow evaluation of canine venous flaps. Plast Reconstr Surg 82: through venous flap has been measured quantitatively. 319, 1988 The following four experimental models of a flow5. Honda T, Nomura S, Yamauchi S.etal: The possible applications through venous flap capable of survival, have been of a composite skin and subcutaneous vein graft in the replantation of reject amputated digits. Brit I Plast Surg 37: reported: 1) the saphenous venous flap in the dog, 607, 1984 reported by Baek et al.,9 Thatte et al.,10 and Amarante 6. Tsai TM, Matiko ID, Breidenbach W, Kutz IK: Venous flaps in et alu; 2) the cephalic venous flap, reported by Sasa digital revascularization and replantation. I Reconstr Microsurg 3:113, 1987 et a!.4; 3) the flow-through venous flap in the rabbit 7. Inada Y, Fukui A, Maeda M, et al.: The sliding venous flap using the thorco-epigastric vein, reported by Matsucovering skin defects with poor blood supply in the lateral shita et al.n; and 4) our flow-through venous flap in the aspect of fingers. Brit I Plast Surg 44:368, 1991 12 8. Fukui A, Inada Y, Maeda M et al. Pedicled and "flow-through" rabbit ear. All experimental models except ours were venous flap; Clinical applications. I Reconstr Microsurg 5: grafted on muscle with a good blood supply, so circula235, 1989 tion from the graft bed can certainly not be ignored in 9. Baek SM, Weinberg H, SongY etal: Experimental studies in the survival of venous island flaps without arterial inflow. Plast those cases. In contrast, no models in which survival Reconstr Surg 7:88, 1985 sites were intentionally distinguished from necrotic 10. Thatte RL, Thatte MR: A study of the saphenous venous island ones have been reported, except for our newly-develflap in the dog without arterial inflow using a nonbiological conduit across a part of the length of the vein. Brit | Plast oped experimental model. These experimental results Surg 40:11, 1987 suggest that our model could become a basic experi11. Amarante |, Costa H, Reis I, Soares R: Venous skin flaps: An mental model, in which the influence of various factors experimental study and report of two clinical distal island flaps Brit I Plast Surg 41:132, 1988 on the survival of the flow-through venous flap could be analyzed quantitatively, from the viewpoint of sur- 12. Matsushita K, Tsai TM, Firrell |C: Blood flow and tissue survival in the venous flap (Abstract). I Reconstr Microsurg 7:146, vival width and area. 1991

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JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 4

An experimental study of the flow-through venous flap: investigation of the width and area of survival with one flow-through vein preserved.

A quantitative analysis was undertaken to investigate the width and area of survival of flow-through venous flaps in 20 ears of 10 rabbits. The 3.0- x...
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