A new flap model in rats: iliac osteomusculocutaneous 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.

Blood Supply to the Integument of the Abdomen of the Rat: A Surgical Perspective

BACKGROUND

Many fundamental questions regarding the blood supply to the integument of the rat remain to be clarified, namely the degree of homology between rat and humans. The aim of this work was to characterize in detail the macro and microvascular blood supply to the integument covering the ventrolateral aspect of the abdominal wall of the rat.

METHODS

Two hundred five Wistar male rats weighing 250-350 g were used. They were submitted to gross anatomical dissection after intravascular colored latex injection (n = 30); conversion in modified Spalteholz cleared specimens (n=10); intravascular injection of a Perspex solution, and then corroded, in order to produce vascular corrosion casts of the vessels in the region (n = 5); histological studies (n = 20); scanning electron microscopy of vascular corrosion casts (n = 10); surgical dissection of the superficial caudal epigastric vessels (n = 100); and to thermographic evaluation (n = 30).

RESULTS

The ventrolateral abdominal wall presented a dominant superficial vascular system, which was composed mainly of branches from the superficial caudal epigastric artery and vein in the caudal half. The cranial half still received significant arterial contributions from the lateral thoracic artery in all cases and from large perforators coming from the intercostal arteries and from the deep cranial epigastric artery.

CONCLUSIONS

These data show that rats and humans present a great deal of homology regarding the blood supply to the ventrolateral aspect of the abdominal integument. However, there are also significant differences that must be taken into consideration when performing and interpreting experimental procedures in rats.

A Model of Free Tissue Transfer: The Rat Epigastric Free Flap

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.

VIABILITY OF VASCULARIZED BONE GRAFT FROM THE ILIAC CREST USING THE ILIAC BRANCH OF THE ILIOLUMBAR ARTERY: EXPERIMENTAL STUDY ON RATS

Objective: Through an experimental model, our aim was to create inferences about the viability of vascularized bone grafts from the iliac crest in rats and investigate their histological features. Methods: Twenty-one rats were used, divided into two groups: the first consisted of animals that were subjected to the technique of vascularized bone graft pedicled onto the iliac branch of the iliolumbar artery; the second (control group) underwent the same procedure as performed on the first group, with the addition of ligation of the vascular pedicle. The viability of the bone grafts was observed for three weeks, by means of direct observation of the graft, histology and immunohistochemistry. Results: All the vascularized grafts evaluated in the first week showed viability according to direct observation, histology and immunohistochemistry. However, in the second and third weeks, direct observation showed that 75% of the grafts were unviable, while histological analysis and immunohistochemistry showed that 50% were unviable. Conclusions: Some grafts that are designed to be vascularized became unviable and began to behave like non-vascularized grafts under direct observation and histology. Despite the possibility of failure, use of vascularized bone grafts should be encouraged, because descriptive histology shows greater cell density in the medullary bone portion, and osteocytes that function better regarding deposition of bone matrix, with preservation of the intraosseous vascular network.

A pedicled muscle flap based solely on a neural pedicle

We tested the hypothesis that the intrinsic vascular plexus of the motor nerve could support viability in a rat hindlimb muscle flap. In a preliminary study, we examined the course and vascularity of the sciatic nerve, the peroneal nerve, and the peroneous longus muscle in the rat hindlimb via anatomic dissection, microangiography, and histologic study (n = 10 animals). On the basis of this examination, the peroneous longus muscle was chosen as our experimental model in this study. In 12 animals, the peroneus longus was acutely elevated, which severed all tendinous and vascular structures, this left the muscle pedicled on the motor nerve only (Group I). Animals in Group II underwent a staged elevation of the flap with division of the vascular pedicle, the tendon of insertion, and the tendon of origin during separate procedures that were 5 days apart (n = 12). Muscle viability was evaluated by gross inspection, measurement of muscle weight and length, nitroblue tetrazlium (NBT) staining, microangiography, and histology. NBT staining demonstrated that immediate elevation of the peroneus longus muscle flaps led to an average necrotic area of 80.6% +/- 9.8% (Group I). A significant improvement in viability was observed for muscle flaps of animals in Group II, with peroneus longus muscle necrosis averaging 25.6% +/- 9.3%. Microangiography demonstrated that the intrinsic vascularity of nerve was increased dramatically in Group II. These data support the hypothesis that the intrinsic vascular plexus of the motor nerve of a skeletal muscle can support at least partial viability of a muscle flap. However, this vascular axis is inadequate to support complete viability of a muscle flap if the flap is elevated immediately. If a staged elevation affects a surgical delay, the viability of a muscle flap elevated on a neural pedicle can be increased significantly. With adjustments in the delay procedure, this strategy may allow transfer of muscle flaps when maintenance or reconstitution of the primary vascular axis is not possible.

Cross-site anastomosis for a free flap with a long pedicle in the rat

We describe a simple and reliable technique for tunneling of the vascular pedicle of the free flap with a long pedicle, that may otherwise cause twisting and/or kinking of the pedicle. There are two modifications of the technique. In the cross-groin anastomosis modification, using a haemostat in a blunt manner, a suprapubic subcutaneous tunnel is created between two groin regions. The vascular pedicle of the flap is pulled and passed through this tunnel to the contralateral region. While the anastomoses are done on one site, the flap is inserted to the contralateral groin. In the second modification ('groin anastomosis-cross dorsum flap insert procedure'), the flap is transferred to the dorsum of the rat at approximately the same level of the groin. Using a haemostat, a large subcutaneous tunnel safe enough for the pedicle is created between the groin region and the rat dorsum lateral to the hip region. The anastomoses are done in the groin region, and the flap is inserted on the dorsum. This technique was used in 16 animals, with a free cutaneous maximus muscle musculocutaneous flap transfer based on the axillary vessels being done in eight animals; and a posterior thigh perforator-based flap based on the popliteal vascular pedicle in the remaining eight. Both groups had a pedicle length of approximately 4 cm, with a 100% survival rate. In conclusion, the technique is simple, reliable, and can be easily carried out without necessitating special procedures. It provides a straight course for the vascular pedicle with tension-free anastomosis by appropraitely adjusting the distance of the vascular anastomosis and flap insertion site.

A new composite flap model in the rat: combined cremaster muscle and pubic bone flap

BACKGROUND

We introduce a new model of combined cremaster muscle and pubic bone flap based on a single pedicle consisting of the osseous branch of pubic bone and external spermatic vessels of cremaster muscle in continuity with the pudic-epigastric artery (PEA).

METHOD

Thirty male Sprague-Dawley rats weighing 200 to 250 g were used in this study. In 10 rats PEA, a branch of the iliac artery was dissected throughout its entire course for the anatomic study. We observed that after giving the external spermatic artery to the cremaster muscle and external pudendal branch to the penis, the PEA continued its course over the ipsilateral pubic bone that was thought to nourish the pubic bone. In 20 rats, the flap was raised on the PEA for the flap study. Five flaps were used for microangiographic study. Remaining 15 rats were used for scintigraphic assessment and dye injection and histologic study.

RESULTS

Microangiographic evaluation revealed the vascularity of all components of the flap as provided by the pedicle. Bone scintigraphy performed at 7th postoperative day demonstrated radionuclide uptake by the bone segment of the flap, indicating the bone viability. In addition, the dye injection study revealed ink staining within blood vessels of the cortex and the marrow of the pubic bone.

CONCLUSION

To the best of our knowledge, this is the first report describing the combined cremaster muscle and pubic bone flap model in the rat. It seems to have an important advantage over the other composite osteomuscular flap models in terms of the cremaster muscle being suitable for the intravital microscopy. Besides being harvested from a small animal species, it is reliable, versatile, and relatively easy to dissect with quite long isolated vascular pedicle, which allows a greater range of flap displacement. It can be used for different applicability including microcirculatory, pharmacologic, physiological, biochemical, and immunologic studies, as well as for the transplantation studies.

A supermicrosurgical flap model in the rat: a free true abdominal perforator flap with a short pedicle

BACKGROUND

Perforator flaps have recently gained considerable popularity in reconstructive surgery, and their importance and advantages over conventional flaps have been widely accepted. Given the improvements in microsurgical techniques, researchers have encouraged the search for further perforator flap sources, such as a perforator flap with a short pedicle only. The purpose of this study was to describe a true perforator flap model with a short vascular pedicle in the abdominal region in the rat.

METHODS

Twenty-six adult Sprague-Dawley rats weighing 400 to 500 g were used. In 10 rats, the perforator vascular anatomy of the abdominal region was determined by anatomic dissection. In the remaining 16 rats, a true abdominal perforator-based flap was created based on a short segment of deep epigastric vessels. In eight rats, the flap was transferred to the groin region as a free flap, and anastomosis was performed between the artery and vein of the flap and the superficial inferior epigastric artery and vein of the recipient site. In addition, in two of these flaps, the long thoracic vein of the flap was anastomosed to the femoral vein. In the remaining eight rats, the flap was transferred to the groin region, but in this group anastomosis was not performed. The latter group was designated as the control group.

RESULTS

The skin islands of seven free perforator flaps survived completely, and the one remaining flap was determined to be necrotic. All the flaps in the control group underwent complete necrosis.

CONCLUSIONS

Not only is the free abdominal perforator flap a reliable and true perforator flap model for future physiological, biological, and pharmacological studies, it is also an excellent self-controlled supermicrosurgical training model for learning proper techniques, meticulous intramuscular dissection of true perforator flaps, and anastomosis of small-caliber vessels.

The Penile Flap in the Rat

Considering both its unique structural and functional properties, the reconstruction of the penis is still a challenging problem in reconstructive surgery. Reconstruction may be required in many situations, including traumas, congenital abnormalities, and female-to-male transsexual surgery. Currently, the only natural reconstructive method for the penis is its microvascular reattachment in amputation cases. In all other situations, and in nonreplantable amputations, there is no alternative but to reconstruct the penis using autologous tissues to create the most similar substitute, hoping for a possible allogeneic transplantation in the future. There are many unresolved issues and unanswered questions related to functional recovery after replantation of the penis. In this study, to overcome these drawbacks and to guide and show the feasibility of allogeneic transplantation of the penis in humans in the future, we describe a penile composite tissue flap based on the internal pudendal artery and its autotransplantation in an economical animal species. Fifty adult male Sprague-Dawley rats weighing 400 to 500 g were used. In 20 rats, the vascular anatomy of the male perineal region was determined by anatomic dissections. Based on this anatomic study, the penile composite flap was created based on the internal pudendal vessels. In 10 rats, the penile flap was raised as an island flap based on its vascular pedicle and replaced in situ. In 10 rats, distant flap transfer was accomplished to determine the feasibility of the flap being transferred as a free flap and to demonstrate the viability of the flap components in a heterotopic region. For this purpose, the flap was transferred to the groin region performing anastomoses between internal pudendal vessels and superficial epigastric vessels. In the control group (n=10), while the same surgical procedure was performed, the flap was transferred to the groin region but no anastomosis was performed. The procedure required approximately 3 to 4 hours of operating time in the free flap group. Five of the animals died in the early postoperative days, while all others survived. Direct observation and microangiography were used to assess the viability of the flaps. On the basis of direct observation on the seventh postoperative day, all the pedicled flaps survived completely. In the free-flap group, all but 1 of the vascularized flaps showed complete survival, whereas all the nonvascularized flaps completely necrosed. The authors conclude that the penile flap of the rat offers the following advantages: (1) the composite tissue flap is harvested from a small animal species, (2) the flap is an exact representation of the clinical original penile composition, (3) it can be transferred as a free flap without the need for an isogeneic animal, (4) the vascular pedicle is consistent and allows for microvascular anastomoses. The flap will provide a means for future physiological studies, especially for replantation cases. The feasible autotransplantation of the penile flap with successful results will also guide researchers towards the future allogeneic transfer of the penis in humans.

New experimental flap model in the rat: Free flow-through epigastric flap

This study describes a free flow-through flap model in the rat for use in the evaluation of the physiologic and hemodynamic characteristics of this type of flap in clinical practice. The rat is a preferred animal model because it is inexpensive, readily available, and reliable. There is no free flow-through flap model available for laboratory animals, although this model gained popularity in clinical use recently. Twenty Wistar rats weighing 200-250 g were used in our experiment. In 5 rats, the vascular anatomy of the groin and proximal thigh region was determined by anatomic dissection. The experimental design consisted of two groups. In the experimental group (N = 5), a flow-through epigastric skin flap was harvested based on the femoral artery, preparing both its proximal and distal stumps. The flap was transferred to the contralateral groin, and end-to-end vascular anastomosis was performed between a proximal and distal stump of the femoral arteries of the flap and recipient site. The proximal stump of the femoral vein of the flap was anastomosed to the femoral vein of the recipient site. The control group was divided into two subgroups. In all control group rats (N = 10), the flap was harvested in the same manner, and transferred to the contralateral groin, but standard free-flap procedure with one artery and one vein anastomosis was performed in 5 rats (conventional free-flap subgroup), and anastomosis was not performed between the flap and the recipient site in the remaining 5 rats (graft subgroup). Survival of the flap was evaluated on postoperative day 7 by direct observation, and microangiography was performed to delineate the vascularity of the flow-through flap. The results showed that all flaps survived in the experimental group and the conventional free-flap subgroup of the control group, whereas in the graft subgroup, all flaps underwent total necrosis. The authors conclude that the flow-through epigastric flap for the rat is a simple and reliable model for future physiologic and pharmacologic studies.

New experimental composite flap model in rats: gluteus maximus-tensor fascia lata osteomuscle flap

Experimental animal models need to be developed for studies of composite flaps that have often recently been used for defects of both bone and soft tissues. A consistent anatomy, simple surgical technique, and reliable blood flow are essential for the success of experimental flap studies. Here we propose a gluteus maximus-tensor fascia lata osteomuscle flap in rats as a model of these qualities. Gluteus maximus and tensor fascia lata muscles and the adjacent iliac bone segment were combined as a lateral circumflex femoral artery-based flap. To test the reliability of this composite flap, three types of composite tissues were harvested and replaced: osteomusculocutaneous flap, osteomuscle flap, and osteomuscle composite graft. The osteomusculocutaneous flap was elevated by including a skin island over the gluteal region. The osteomuscle graft was formed by deliberately dividing the vascular pedicle of the osteomuscle flap. Direct observation revealed complete necrosis of the skin islands in all osteomusculocutaneous flaps. Microangiography of the flap demonstrated that both muscles and the attached bone were supplied by the pedicle. Dye studies with nitro blue tetrazolium (NBT) and India ink demonstrated dye uptake in both muscle and bone components in osteomuscle flaps. Histological examinations also demonstrated the viability of both tissues only in the flap group. Bone scintigraphy performed in flaps on postoperative day 7 demonstrated radionuclide uptake, confirming perfusion of the bony segment. The gluteus maximus-tensor fascia lata osteomuscle flap is a reliable and simple model for composite flap studies that offers the following advantages: 1) it is a new composite flap which includes bone, 2) it can be dissected easily with the naked eye, without using the microscope, 3) it has a long pedicle for flap displacement, and 4) it is a small animal model.

A New Experimental Flap Model: Free Muscle Perforator Flap

A large number of perforator flap types have been described in experimental and clinical studies. Perforator flaps have been used both as pedicled and free flaps in clinical practice, but only in a pedicled form in animal studies. According to the authors' literature review, a free perforator flap in an animal model has not yet been developed. The purpose of this study was to describe a new free perforator flap model in the rat. A total of 15 Wistar rats weighing 200 to 250 g were used in this experiment. In 5 rats, the vascular anatomy of the popliteal vessels and their relation with adjacent structures were determined by anatomic dissection. In the remaining 10 rats, a posterior thigh perforator-based flap was created based on the distal popliteal vascular pedicle. In 5 rats the flap was transferred to the groin region as a free flap. In the remaining 5 rats the flap was transferred to the groin region, but in this group anastomosis was not performed between the vascular structures of the flap and the recipient femoral vessels. The latter group was designated as the control group. Direct observation and microangiographic techniques were used to assess the viability of the flap. Results showed that the cutaneous islands of all the free flaps survived completely, whereas in the control group all the flaps under-went total necrosis. The authors conclude that the free posterior thigh perforator flap is a reliable and true perforator flap model for future physiologic, biologic, and pharmacologic studies. It offers the following advantages: 1) Arising from the biceps femoris muscle, the musculocutaneous perforator of the flap has a consistent vascular pedicle, 2) it is the first free perforator flap for the rat, 3) it is harvested from a small-animal species, and 4) it can be used without the need for an isogeneic rat.