The oblique rat groin flap

New Chimeric Groin Flap: Experimental Model in Rats

AIM

Increased emphasis is on using tissue substitutes and stem cells to improve flap applicability and survival rates. To accomplish this, the first step is to have a versatile experimental flap, easy to harvest and use as a template. We sought to develop a reliable experimental chimeric groin flap with free mobility and reliable bloods supply that can be twisted, relocated, and integrated easily with other materials.

MATERIALS AND METHODS

Ten male Wistar rats were included. The flap consists of a 2.5-cm skin paddle centered on the medial branch of the inferior epigastric artery and a 4.5/2-cm fat pad supplied by the lateral branch of the inferior epigastric artery. After being raised, flaps were resutured in their anatomical position. Flaps were followed up for 15 days. At the end of the study, the viability of flaps was analyzed by ultrahigh-frequency ultrasound, nontargeted contrast study, and histology assessment.

RESULTS

All flaps survived without significant complications. Nontargeted microbubbles spread evenly in both the superficial and deep flap. Ultrasound assessment at day 15 showed no significant areas of necrosis or edema. Histology examination of 3 random flaps confirmed vessel patency and flap viability.

CONCLUSION

We propose a simple, easy to harvest and reliable experimental flap which offers a main advantage of all-around mobility through its chimeric design. It is a suitable model for bioengineering studies as it can be used as a template for integration of tissue substitutes or stem cells, between its 2 components.

Effects of microarterial anastomosis torsion on survival of oblique groin flap in rats

A microanastomosis might tolerate a torsion up to 360°, but the effects of arterial microanastomosis torsion on the survival of the flap it supplies are unclear. The aim of this study was to investigate the consequences of microarterial anastomosis torsion on the groin flap in rats. Forty Sprague-Dawley rats were divided into five groups. An oblique groin flap was harvested as an island flap and a patch-to-side arterial anastomosis was performed with torsion angles of 0°, 90°, 180°, 270°, and 360°. Six of eight flaps in Group I (0° torsion), six of eight flaps in Group II (90°), three of eight flaps in Group III (180°), and none of the flaps in Groups IV and V (270° and 360°) were found to be viable after 1 week. The patency and flap survival rates observed in Groups II, III, IV, and V were compared with those in Group I using Fisher's exact test. The patency rates and flap survival rates in Groups IV and V were significantly lower compared with those in Group I. Our data show that skin flaps can survive even if their arterial pedicle is anastomosed with a torsion of up to 180°.

In vivo observations of cell trafficking in allotransplanted vascularized skin flaps and conventional skin grafts

The problem of allogeneic skin rejection is a major limitation to more widespread application of clinical composite tissue allotransplantation (CTA). Previous research examining skin rejection has mainly studied rejection of conventional skin grafts (CSG) using standard histological techniques. The aim of this study was to objectively assess if there were differences in the immune response to CSG and primarily vascularized skin in composite tissue allotransplants (SCTT) using in vivo techniques in order to gain new insights in to the immune response to skin allotransplants. CSG and SCTT were transplanted from standard Lewis (LEW) ad Wistar Furth (WF) to recipient transgenic green fluorescent Lewis rats (LEW-GFP). In vivo confocal microscopy was used to observe cell trafficking within skin of the transplants. In addition, immunohistochemical staining was performed on skin biopsies to reveal possible expression of class II major histocompatibility antigens. A difference was observed in the immune response to SCTT compared to CSG. SCTT had a greater density cellular infiltrate than CSG (p<0.03) that was focused more at the center of the transplant (p<0.05) than at the edges, likely due to the immediate vascularization of the skin. Recipient dendritic cells were only observed in rejecting SCTT, not CSG. Furthermore, dermal endothelial class II MHC expression was only observed in allogeneic SCTT. The immune response in both SCTT and CSG was focused on targets in the dermis, with infiltrating cells clustering around hair follicles (CSG and SCTT; p<0.01) and blood vessels (SCTT; p<0.01) in allogeneic transplants. This study suggests that there are significant differences between rejection of SCTT and CSG that may limit the relevance of much of the historical data on skin graft rejection when applied to composite tissue allotransplantation. Furthermore, the use of novel in vivo techniques identified characteristics of the immune response to allograft skin not previously described, which may be useful in directing future approaches to overcoming allograft skin rejection.

Recipient damage after musculocutaneous transplant rejection

BACKGROUND

In the event of a composite allograft failure, damage to the recipient tissues may make retransplantation impossible. This study aimed to quantify the damage after composite allograft failure to assess whether retransplantation is feasible.

METHODS

Rats (n=6) in the group I received composite musculocutaneous flap allotransplants (WF-->Lew) with immunosuppression allowing healing-in of the allograft before being tapered allowing rejection. At full rejection, the recipient vascular pedicle was examined, biopsies of the recipient tissue bed were taken and graded for damage, and in vitro assays were performed. Groups II (allograft without immunosuppression, n=7), III (isograft with immunosuppression, n=5), and IV (isograft without immunosuppression, n=6) were included to attempt to identify the contributions of the rejection process, immunosuppression, and healing to recipient tissue damage.

RESULTS

The vascular pedicle was patent to within 1 mm of the anastomosis in all rejected allografts. Furthermore, it was possible to retransplant after full rejection. There was minimal damage to the recipient tissues at the time of full rejection in group I. In contrast, group II had significantly more damage (P<0.05) to recipient muscle and skin. This correlated with more severe immune reaction with more than 100 times antibody production in group II compared with group I. Groups III and IV had little recipient tissue damage.

CONCLUSIONS

These results suggest that it is possible to retransplant after rejection of a musculocutaneous transplant while on immunosuppression. Furthermore, the second transplant will not be limited in form or function by recipient tissue bed damage.

Microvascular free tissue transfer for gene delivery: in vivo evaluation of different routes of plasmid and adenoviral delivery

Transfer of healthy autologous tissue as a microvascular free flap facilitates reconstruction during ablative cancer surgery. In addition to filling surgical defects, free flaps might concentrate viral vectors at the tumour bed and mediate local therapeutic effects. We evaluated the magnitude, topography and duration of luciferase gene expression after plasmid and adenoviral delivery in rat superficial inferior epigastric (SIE) flaps. For plasmid delivery, luciferase expression was significantly increased by all transduction routes (topical, intraflap injection, intravascular) (P<0.01) at day 1, but not at day 7. The spread of luciferase expression was significantly different between the 4 groups at 1 day (P=0.026) and was greatest for flaps transduced by intravascular injection. For adenoviral transduction, total radiance was significantly different between the transduced groups at 1, 14 and 28 days (P<0.05 for all comparisons). The highest levels of radiance were seen in the intravascular group. There was a statistically significant difference in the spread of light emission between the 3 groups at 1 (P=0.009) and 14 (P=0.013) days, but this was no longer evident at 28 days. Intravascular adenoviral delivery yields high-level, diffuse and durable gene expression in rat SIE flaps and is suitable for examination in therapeutic models.

Cutaneous Viability in a Rat Pedicled TRAM Flap Model

BACKGROUND

The transverse rectus abdominis musculocutaneous (TRAM) flap is widely used in breast reconstruction. However, morbidity with its pedicled form has resulted in a high incidence of complications. The authors conducted a study of the pedicled TRAM flap procedure in 35 female Wistar rats based on the left deep inferior epigastric vessel, which was nondominant.

METHODS

In all the rats, the flap was divided into four areas: area 1, the skin on the left rectus abdominis muscle pedicle; area 2, the skin contralateral to the midline, opposite of the left rectus abdominis muscle pedicle; and areas 3 and 4, the skin lateral to areas 1 and 2, respectively. The occurrence, percentage, and distribution of necrosis on the TRAM flap surface were determined.

RESULTS

Necrosis was observed at four statistically distinct and significant levels, distributed in the four different areas as follows: area 1, 9 percent; area 2, 37 percent; area 3, 74 percent; and area 4, 100 percent (p < 0.001). The median proportion of necrosed flap surface was 15 percent (range, 2 to 42 percent).

CONCLUSIONS

The determination of necrosis allowed us to identify three distinct levels of necrosis: area 4 with the highest scores, area 3 with intermediate scores, and areas 1 and 2 with the lowest scores (p < 0.001). Areas 1 and 2 of the TRAM flap surface had less incidence of necrosis, contrary to the lateral areas 3 and 4, in which cutaneous necrosis was found to be more significant.

Free flap transfer to the dorsum of the rat: a new technique to avoid autocannibalization in free flap studies

In this report the authors describe a new method that avoids autocannibalization by free transfer of a flap to the dorsum of the rat by means of a simple exposure technique. A total of 22 Wistar rats of both sexes (weight, 200-290 g) were used in this experiment. An anatomic study performed in 12 rats revealed that a wide exposure could be created in the axillary fossa by retracting the inferior tip of the scapular bone superiorly (after severing its attachments with the deep extrinsic back muscles), the latissimus dorsi muscle laterally, and the serratus anterior muscle medially. Furthermore, after obtaining vessel diameter measurements, it was ascertained that the subscapular and the lateral thoracic vessels could serve as the recipient vessels. Based on the anatomic study, a total of 10 conventional groin cutaneous flaps, measuring 2 x 3 cm in size, were harvested based on the femoral vessels and transferred to the dorsum of the same animal by the exposure method as just described, with microvascular anastomoses performed between the femoral vessels of the flap and either the subscapular artery and the lateral thoracic vein (N = 5) or the lateral thoracic artery and vein (N = 5). Results showed that 9 of the 10 transplanted flaps were totally viable on postoperative day 7, giving a success rate of 90%, with one failing flap belonging to the latter group. The authors conclude that by this simple method of recipient vessel exposure in the axillary fossa, free flap transfer to the dorsum of the rat is a simple and reproducible technique by microvascular anastomoses performed between the pedicle vessels of a flap and the subscapular artery and the lateral thoracic vein. This model offers the unique advantage of a dorsally located flap that is protected by autocannibalization. Moreover, daily observation and monitoring of the flap are easy and practical without the need to have the animal wear protective material such as vest.

Platelet-derived growth factor-AA-mediated functional angiogenesis in the rat epigastric island flap after genetic modification of fibroblasts is ischemia dependent

BACKGROUND

The aim of this study was to induce therapeutic angiogenesis in ischemically challenged flap tissue by means of gene transfer.

METHODS

Isogenic rat fibroblasts were retrovirally transfected to produce platelet-derived growth factor (PDGF)-AA. Stable gene expression was monitored by PDGF-AA enzyme-linked immunosorbent assay. Eighty animals were divided into 2 groups (1 and 2), each with 4 subgroups. The angiogenic target was a 7 x 7-cm epigastric island flap used as a necrosis model. Group 1 received flap treatment 1 week before flap elevation: 10(7) genetically modified fibroblasts, expressing PDGF-AA (genetically modified fibroblasts) plus 1 mL of Dulbecco's modified Eagle's medium (DMEM) (1A), 10(7) nonmodified fibroblasts (NMFB) plus 1 mL of DMEM (1B), 1 mL of DMEM (1C), and 1 mL of sodium chloride 0.9% (1D). All substances were injected at evenly distributed spots into the panniculus carnosus of the entire flap. Group 2 had the same flap treatment at the day of flap elevation. All flaps were sutured back. Seven days later, the flaps were harvested and examined both clinically, histologically, and immunohistochemically.

RESULTS

In vitro, the GMFB produced up to 117.9 +/- 57.2 ng of PDGF-AA/mL medium during a 4-day period, compared with 0.7 +/- 0.6 ng of PDGF-AA/mL medium produced by NMFB in the same time period. In vivo production of PDGF-AA in flaps amounted to 1.3 +/- 0.7 ng of PDGF-AA/1 microL flap tissue for group 1A and 1.7 +/- 1.1 ng of PDGF-AA/1 microL flap tissue for group 2A seven days after cell transplantation. Fibroblasts persisted in all flaps from groups 1A, 1B, 2A, and 2B without major inflammatory reaction. Clinically, group 2A developed significantly less flap necrosis compared with all other groups, including group 1A. Accordingly, only group 2A gave significant histologic and immunohistochemical evidence for enhanced angiogenesis within the flap tissue.

CONCLUSIONS

After retroviral gene transfer, isogenic rat fibroblasts produce high amounts of PDGF-AA in vitro. In vivo, PDGF-AA can be detected in flaps receiving genetically modified fibroblasts, which suggests survival of the implanted fibroblasts in this model. PDGF-AA produced by GMFB can induce flap angiogenesis only under ischemic conditions in this model. Transplantation of PDGF-AA-overexpressing fibroblasts results in higher flap survival in this model.

Perforator-based flap in rats: a new experimental model

A new type of flap, the perforator-based flap, has been described in the last decade. It has been used successfully as a pedicle or free flap by many plastic surgeons. There is no animal model for research, although these flaps have gained popularity in clinical use. We created a perforator-based flap model in the rat (a perforator-based flap group and two control groups; 10 rats in each group) and evaluated the survival characteristics of the new flap. The abdominal skin flap was elevated based on the second perforator of the right superior deep epigastric artery and then sutured to its original bed. In the first control group, the same flap was elevated with a subcutaneous pedicle without any perforator; in the second control group, a right-sided, random-pattern pedicle abdominal skin flap with the same dimensions and location was elevated and sutured to its original bed. Flap survival was studied, and microangiography and histologic studies were performed. The amount of viable skin in the three groups was compared 1 week later. The area of surviving skin paddles in the experimental group ranged from 74 to 83 percent; in the first control group, it was 0 percent; and in the second control group, it ranged from 29 to 44 percent (p < 0.001 and p < 0.001, respectively). There was a predictable and constant area of necrosis in the model. The results of this study demonstrate that most of the abdominal skin of the rat can survive on the basis of a single musculocutaneous perforator vessel. This flap can be easily elevated, and it can be used as a reliable model for flap research.

Experimental model for transplantation of a modified free myocutaneous gracilis flap to an irradiated neck region in rats

In 102 Wistar rats (male, weight 300-500 g), a modified free myocutaneous gracilis flap was obtained from the groin and transplanted to the neck. To create a pre-irradiated transplant bed, a local area of the neck was irradiated preoperatively with 30 Gy (fractionation: 3 x 10 Gy) in 30 animals, and with 50 Gy (fractionation: 5 x 10 Gy) in a further 30 animals. The interval between preoperative irradiation and transplantation was 4 weeks. Forty-two animals received no such preoperative radiation. The evaluation of healing and the success of the transplanted flap was based on a clinical assessment, carried out on postoperative days 1 7. Testing for significant differences was done nonparametrically using the Kruskal-Wallis test. The survival rate in the nonirradiated animals was 86%. In contrast, the healing of the free flaps in the pre-irradiated transplant bed was significantly lower (P=0.003) 76%, after irradiation with 30 Gy and 50% after 50 Gy. The significant difference (P=0.020) in survival rates after irradiation with 30 and 50 Gy was evidence for the dependence of successful healing on the preoperative radiation dose. Transplantation of the free myocutaneous gracilis flap to a previously irradiated transplant bed in the region of the neck is a suitable model for investigating the healing of free transplants to irradiated tissue. The success rate observed in non-irradiated transplant beds is comparable to that seen with other flap models in rats.

Cellular changes in denervated tissue during wound healing in a rat model

There is increasing evidence that innervation, possibly mediated via neuropeptides, promotes wound healing. This study presents data on the early cellular events during healing in denervated tissue. Free oblique groin flaps were raised on 25 adult Sprague-Dawley rats. Excisional wounds were placed within the flap and in two control sites, the contralateral inguinal region and the thorax. The absence of innervation in the free flap wounds was confirmed 10 days after surgery by indirect immunofluorescence with a pan-neuronal marker. The cellular infiltrate of the wounds was analysed immunohistochemically with a panel of antibodies to rat macrophages and monocytes (ED1), rat B lymphocytes (CD45R) and T lymphocytes (CD2). The immunostained cellular infiltrate was quantified at 2, 4, 7 and 10 days postoperatively. Our results show that denervated wounds have a significantly lower macrophage and T-lymphocyte count at day 4 of wound healing (P < 0.05). Inflammatory cells, particularly macrophages, are known to play an important part in wound healing and their reduced chemotaxis in denervated tissue may be related to the observed delay in wound closure.

The development of neovascularisation in flap perfabrication with vascular implantation: an experimental study

Femoral arteriovenous pedicles were implanted beneath the abdominal skin in rats (n = 30) to investigate the development of neovascularisation over time. New vessel formation was assessed by micro-angiography and quantified under light microscopy. Flap viability was assessed by dye injection studies at different time intervals. Two weeks after implantation of the vascular pedicles, neovascularisation was confined to the vicinity of the arteriovenous pedicle only and none of the flaps were viable. At 4 and 6 weeks, 4 out of 6 flaps were viable, with new vessel formation being widespread throughout the subcutaneous tissue. All flaps were viable at 8 and 12 weeks. Neovascularisation in the dermis up to the epidermis was observed after 8 weeks. Neovascularisation in the panniculus carnosus showed a steady increase after 6 weeks. There was a decrease in the total number of vessels at 12 weeks compared to 8 weeks but at 12 weeks the diameters of the vessels were considerably larger. Flap survival was best predicted by the amount of neovascularisation in the panniculus carnosus. In this experimental model, it is concluded that prefabricated flaps should be raised at 8 weeks instead of 4 or 6 weeks after the implantation of an arteriovenous pedicle, to reduce the risk of flap failure.

Non-revascularized epigastric free flap: no all-or-none survival pattern

We have previously shown that the epigastric flap in Dark Agouty rats, measuring approximately 6 x 4 cm with borders related to well-defined anatomical structures, does not exhibit an all-or-none survival pattern. This study was designed to investigate the survival pattern of non-revascularized epigastric flaps in three other rat strains (Sprague-Dawley, Brown-Norway, and Lewis). In concordance with our earlier observations, but in contrast to reports by many other groups, in none of the used strains was an all-or-none survival pattern observed. Survival varying from 2 to 30% (mean, 12%) of the original flap, without significant differences between the strains, was found. The locations of survival exhibited a clear pattern, probably owing to the fat pad in the subcutis and revascularisation from the recipient wound edges.

Neovascularisation precedes neural changes in the rat groin skin flap following denervation: an immunohistochemical study

We have employed immunohistochemical techniques to study neural and vascular changes in rat skin flaps. Following partial or total denervation, flaps were studied at 4, 7 or 12 days using antisera to PGP 9.5 (panneural marker), the neuropeptides CGRP (sensory nerves) and CPON (adrenergic nerves) and an endothelial marker VWF. In partially denervated flaps, moderate increases in PGP-immunoreactive (PGP-IR) and CGRP-IR nerves and a mild increase in CPON-IR nerves in immediate surrounding skin preceded smaller increases in similar nerves around the pedicle. Following total denervation, mild increases in all nerve types at these locations were accompanied by a marked increase of these nerves in distant surrounding skin, 1-2 cm from the suture line. A gradual increase in endothelial cell staining (VWF) of blood vessels was seen in surrounding skin, flap beds and pedicles. Angiogenesis preceded flap reinnervation which occurred initially from surrounding skin, and later from the base, with sensory fibres appearing first.

Survival characteristics of the epigastric free flap in DA-rats

Epigastic flaps measuring approximately 6 x 4 cm with borders related to well-defined anatomical structures were isografted (Dark Agouty to Dark Agouty inbred rats) with or without anastomosing their epigastric pedicle, after various periods of ischaemia, ranging from 0 to 120 h. During the ischaemic insult the flaps were stored at 0 degrees C in a hypertonic citrate solution. The non-revascularized flaps exhibited survival percentages varying from 2 to 34% (mean, 16%) of the original flap,. independent of the storage interval. The flaps that were revascularized after ischaemia had a 100% survival when transplanted immediately after isolation and following 48 h of cold storage. Mean survival percentages of 78% after 72 h of ischaemia, 32% after 96 h, and 4% after 120 h of ischaemia were found. It is concluded that the model described in this study is suitable for free flap research, because of its delineated borders. However, when the area of flap survival is lower than 30% in revascularized flaps there is a distinct likelihood that the flaps have survived regardless of the pedicle as simple Wolfe or composite grafts. Results must therefore be interpreted with great care.

Free flap transfer of the cutaneous maximus muscle in the rat: comparison to the latissimus dorsi muscle flap

A new rat model of free muscle flap transfer is presented. Microvascular transplantation of the cutaneous maximus muscle flap is performed at the groin site, with anastomosis of the axillary vessels to the appropriate femoral vessels. This muscle flap has many useful attributes for experimental manipulation. It has a high success rate following transplantation, the anatomy is consistent, the dissection is straightforward, the length of pedicle is relatively long (10 mm), the vessels for repair are of sufficient size (1.0-1.35 mm diameter), and the microsurgical procedure can be performed in a relatively short period. The donor site deficit causes minimal impairment to animal mobility, and no evidence of limb ischemia is noted after ligation of the axillary vessels. The cutaneous area adjacent to the muscle is perfused by muscular perforators supplied by the flap pedicle; thus a skin island may be used to monitor the flap or to create a composite myocutaneous transfer. The cutaneous maximus muscle has mixed muscle types and anatomic dimensions similar to those of the latissimus dorsi muscle, and it provides ample tissue for pharmacological and biochemical studies, yet it presents easier dissection and microanastomoses than the latissimus flap, with more potential for versatility in application. The advantages of this muscle flap make it a very useful experimental model for flap transfer research.

Reperfusion injury in rat adipomusculocutaneous flaps: an ultrastructural and microangiographic study

Electron microscopy (EM), microangiography (MA) and histological studies were carried out to demonstrate the vascular basis of ischaemic and reperfusion injury in rat adipomusculocutaneous free flaps which had been stored under normothermic conditions (37 degrees C) for specific periods of time. MA revealed that areas destined to die reperfused for at least 6 h in this model. EM showed progressive endothelial damage as a result of both storage and reperfusion. The use of the iron chelator desferrioxamine (DFX) did not benefit the endothelium or improve salvage of ischaemic flaps.