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

Rat Perforator and Skin Vessels Vascular Mapping: An Original Anatomical Study About 140 Vessels and Literature Review

INTRODUCTION

Recent microsurgical reconstruction techniques benefit from the use of skin and perforator flaps that spare the donor sites. Studies on these skin flaps in rat models are numerous but there is currently no reference regarding the position of the perforators, their caliber, and the length of the vascular pedicles.

METHODS

We performed an anatomical study on 10 Wistar rats and 140 vessels: cranial epigastric (CE), superficial inferior epigastric (SIE), lateral thoracic (LT), posterior thigh (PT), deep iliac circumflex (DCI) and posterior intercostal (PIC) vessels. The evaluation criteria were the external caliber, the length of the pedicle, and the position of the vessels reported on the skin surface.

RESULTS

Data from the six perforator vascular pedicles are reported, with figures illustrating the orthonormal reference frame, the representation of the vessel's position, the cloud of points corresponding to the various measurements, and the average representation of the collected data. The analysis of the literature does not find similar studies; the different vascular pedicles are discussed as well as the limitations of our study: evaluation of cadaver specimen, presence of the very mobile panniculus carnosus, other perforator vessels not evaluated as well as the precise definition of perforating vessels.

CONCLUSIONS

Our work describes the vascular calibers, pedicle lengths, and location of birth and arrival at the skin of the perforator vessels PT, DCI, PIC, LT, SIE, and CE in rat animal models. This work, without an equivalent in the literature, lays the foundation for future studies about flap perfusion, microsurgery, and super microsurgery learning.

Perfusion of muscle flaps independent of the anatomical vascular pedicle: Pedicle autonomy

INTRODUCTION

Free muscle flaps are being used more commonly for complex lower limb reconstruction. Up to 33% of flaps used to reconstruct lower limb trauma will require an orthopaedic procedure after reconstruction. To date there have been only case reports detailing the variable survival of muscle flaps after actual or simulated pedicle injury and the process and timeframe of neovascularisation remains undefined. We aim to show that perfusion of a muscle flap is possible after injury to its anatomical vascular pedicle.

METHODS

Pedicled muscle flaps were raised and transposed to a cutaneous inset on the chest wall in a rodent model. Each flap was subjected to simulated pedicle injury at a variable time. Allocation was by computer randomisation. Flap perfusion was assessed before and after pedicle injury followed 48 h later by sacrifice of the animal and static angiography of the flaps.

RESULTS

By the 21st day after inset, all flaps survived simulated pedicle injury. Prior to this, flap survival was significantly lower (p = 0.017, Fisher's Exact Test). Clinical signs at the time of pedicle injury did not predict flap survival. Most new vessels form at the distal part of the inset (p < 0.01, ANOVA). The total number does not change with time (p = 0.82, ANOVA). New vessels anastomose preferentially with skin. The fall in perfusion after pedicle ligation was significant for all groups except the day 35 group (p = 0.53).

CONCLUSIONS

Muscle flaps can perfuse after an injury to the anatomical vascular pedicle through neovascularisation at the inset. These new vessels are evident early but may not function adequately to perfuse the flap. Regional variations in neovascularisation suggest that a gradient of ischaemia drives this process. Inset at the cutaneous level is important, which has implications for buried muscle flaps. The correlation between change in flap perfusion after pedicle injury and flap necrosis suggests a role for the former in determining the capacity of a muscle flap to tolerate a pedicle injury and thereby the approach to re-raising it.

Lateral thoracic artery perforator-based flap: a new experimental model

BACKGROUND

The aim of this study was to describe a new experimental perforator-based flap in rats, supplied by lateral thoracic artery perforator.

METHODS

Through out the study, two control and two experimental groups were created consisting of six rats in each group. In the first control group (group 1), mid-axillary line and the fourth intercostal space intersection were used as the center of the flap. A 3 × 2 cm flap was designed and elevated above the cutaneous maximus muscle by transecting all connections with the muscle. In the second control group (group 2), the flap was extended caudally, and 3 × 6 cm flap was designed. Then, the flap was elevated in the same manner as it was described for group 1. In the first experimental group (group 3) 3 × 2 cm flap and in the second experimental group (group 4) 3 × 6 cm flap were designed like control groups. The flaps were islanded on a single musculocutan perforator arising from lateral thoracic artery. The surviving skin paddle areas were calculated on postoperative day 7.

RESULTS

The flap viability was calculated 0% for control groups (groups 1 and 2), 100% for the first experimental group (group 3), between 33.3% and 37.7% for the second experimental group (group 4; mean ± standard deviation, 34.76% ± 1.92%).

CONCLUSIONS

This new lateral thoracic artery perforator-based flap has a constant anatomy and reliable survival pattern. Also, easy harvesting and the possibility of designing two flaps per animal make this new flap an appealing model for pathophysiological or pharmacologic researches.

Long-term BMP-2-induced bone formation in rat island and free flaps

Ectopic osteoinduction by exogenous bone morphogenetic proteins (BMPs) is rapid but heretofore characterized as transient. A rat model of carrier-free recombinant human BMP-2 intramuscular implantation was used, followed by creation of either an island flap or transplantation of a free flap. BMP-2 injection into an unaltered gastrocnemius, thigh adductor, or cutaneous trunci (thoracic wall) muscle site led to bone resorption at 4 weeks. In contrast, creation of an island or free flap of the muscle/injection site caused the newly formed ossicle to maintain its bony composition with active osteoblastic presence, from 3-8 weeks. Muscle denervation or sectioning of the Achilles tendon (for gastrocnemius injections) did not prevent bone resorption at 4 weeks. There was little osteoclastic activity within de novo bone sites of island- and free flap-injected muscles at 4 and 8 weeks. These data demonstrate that simple injection of BMP-2 into a surgically isolated flap site results in the prolonged presence of de novo bone. These findings suggest that BMP-injected island or free muscle flaps may be used to generate new bone for reconstruction of a bony defect.

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.

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.

Brief ex vivo perfusion with heparinized and/or citrated whole blood enhances tolerance of free muscle flaps to prolonged ischemia

This study investigated the use of heparinized and/or citrated whole blood as a perfusate for enhancing muscle tolerance to warm ischemia. Unilateral cutaneous trunci muscle flaps were harvested from Sprague-Dawley rats and stored for 10 hr at 22-24 degrees C prior to transplantation to the groin. One group served as a non-perfused control. In three experimental groups, the flaps were hand-perfused ex vivo with 1.0 ml of heparinized, citrated, or heparinized and citrated autogenous whole blood at physiological pressures. Perfusion was administered over a 10-min period 5 hr into the ischemic period. Flaps were revascularized on the femoral vessels and then harvested 48 hr following revascularization. Tissue injury was assessed by calculation of flap weight change (indicator of tissue edema), histochemical evaluation of muscle dehydrogenase activity (nitroblue tetrazolium assay), and light microscopy. All perfused groups had significantly higher muscle dehydrogenase activity compared with non-perfused controls (P < 0.005). Perfusion with combined heparin-citrated blood was significantly more protective than perfusion with either anticoagulant alone (P < 0.025). The only statistically significant reduction in percent flap edema was seen in the combined heparin-citrate perfusion of flaps compared with nonperfused controls (P < 0.05). Histologic evaluation confirmed a reduction in tissue edema in the perfused flaps. We conclude that mid-ischemic perfusion with heparinized and/or citrated blood limits the deleterious effects of extended warm ischemia.

In vivo analysis of the microcirculation of osteomyocutaneous flaps using fluorescence microscopy

Previous studies have indicated that freely transferred osteomyocutaneous flaps may fail despite anastomotic patency. While microvascular dysfunction is thought to be one of the major causes for this type of flap failure, little is known of its underlying mechanisms, probably due to the lack of adequate experimental models allowing detailed intravital microcirculatory analysis. Herein we report quantitative analysis of the microcirculation of periosteum, muscle, subcutis and skin by intravital fluorescence microscopy using an osteomyocutaneous free flap model in the hindlimb of rats. The microcirculation of the different tissues was studied after microanastomotic transfer (free flap), and was compared to that after solely elevating the tissue, mimicking a pedicled osteomyocutaneous flap. Transferred flaps, which were exposed to 1 h of ischaemia during the anastomotic procedure, showed a slight but significant decrease (P< 0.05) of functional capillary density in muscle, subcutis and skin when compared with the microcirculation of pedicled flaps, while capillary diameters, red blood cell velocity and blood flow of perfused capillaries remained almost unaffected. The decrease of functional capillary density was associated by a significant (P< 0.05) inflammatory response, as indicated by the increased number of leukocytes adherent to the endothelial lining of postcapillary venules. While the functional capillary density of periosteum was not affected by the free transfer procedure, the inflammatory response was found similar when compared with that observed in muscle and subcutis. Thus, our study indicates that even after a short 1-h ischaemic time period, capillary perfusion failure and leukocyte-endothelial cell interaction are the main events, characterising microvascular dysfunction after free transfer of osteomyocutaneous flaps. Using the model described herein, intravital microscopic analysis of the microcirculation proved an appropriate tool to study the individual microvascular response after free tissue transfer, and may thus be used to evaluate the effectiveness of novel therapeutic regimens which aim at counteracting microcirculatory dysfunction in free osteomyocutaneous flaps.

Intravascular heparin protects muscle flaps from ischemia/reperfusion injury

Heparin has been found to decrease ischemia/reperfusion injury in skeletal muscle and other tissue/organ systems. The timing of heparin administration to the muscle vasculature has not been explored. We investigated the use of heparinized blood as a washout solution during ischemia to reduce ischemia/reperfusion injury. A rat cutaneous maximus muscle free flap was subjected to a 10-hr period of room temperature ischemia, then was heterotopically transplanted to the groin via microsurgical revascularization to the femoral vessels. In three experimental groups, flaps were subjected to brief ex vivo perfusion with autologous heparinized blood, at 2, 5, or 8 hr into the 10-hr ischemic interval. In the two other groups, the flaps were not perfused, and the animals were systemically heparinized either before ischemia or before transplantation, respectively. A control group underwent no flap perfusion or systemic heparinization. After transplantation, flaps were given a 48-hr period of in vivo reperfusion, then were harvested for evaluation. Flaps undergoing ex vivo perfusion or preischemic heparinization had no significant differences in weight gain (edema) compared with flaps receiving posttransplant heparinization or no heparinization (controls). The dehydrogenase staining of muscle biopsies was significantly faster (indicative of viable tissue) for perfused flaps and the flaps for which the animals received preischemic heparinization, when compared with flaps for which the animals received posttransplant heparinization or no heparinization. From these results, we conclude that heparin offers protection from ischemia/reperfusion injury when it can be introduced into the vascular network either prior to or during the ischemia period. These findings suggest the possibility of using heparinized washout solutions to enhance survival in amputated extremities.

Ex vivo perfusion with anticoagulated blood decreases ischemia/reperfusion injury

Rat muscle flaps (cutaneous maximus) were subjected to 4 hours of room-temperature ischemia followed by 44 hours of cold (4 degrees C) ischemia before transplantation. Experimental flaps underwent a 15-minute ex vivo perfusion with heparinized-citrated blood between the warm and cold ischemic treatments; control flaps were not perfused. After 1 or 48 hours of recirculation, muscle dehydrogenase activity was found to be higher in the perfused flaps, indicating better muscle viability. Lipid peroxidation was lower in the perfused flaps, indicating a reduction in free radical generation. Histologic assessment revealed that perfused flaps underwent less injury than unperfused flaps. The findings of this study indicate that replacement of standing blood with anticoagulated blood, with the use of a brief ex vivo perfusion protocol, has a significant protective effect against ischemic injury. The experimental design mimics a realistic point of intervention and presents a paradigm for the clinical treatment of amputated extremities.

Thigh adductor flap: an experimental model for free flap transfer in the rat

A new model of rat muscle free flap transfer is presented. The flap is based on a long pedicle originating from the femoral vessels and continuing down to the distal saphenous margin at the ankle. The distal portion of the semitendinosus muscle is harvested along with the saphenous artery and great saphenous vein. A larger muscle flap may be harvested by including the distal portions of the posterior and anterior gracilis muscles. The flap can be transferred to remote sites on the animal, with a vascular pedicle of up to 3 cm in length. The diameters of the vessels repaired are of standard microsurgical size. This model has distinct advantages of simplicity, speed of dissection, high success rate after microvascular transfer, and versatility in placement of the muscle mass (due to the long pedicle).