A new flap model in the rat

Standardized Pre-clinical Surgical Animal Model Protocol to Investigate the Cellular and Molecular Mechanisms of Ischemic Flap Healing

BACKGROUND

Some of the most complex surgical interventions to treat trauma and cancer include the use of locoregional pedicled and free autologous tissue transfer flaps. While the techniques used for these reconstructive surgery procedures have improved over time, flap complications and even failure remain a significant clinical challenge. Animal models are useful in studying the pathophysiology of ischemic flaps, but when repeatability is a primary focus of a study, conventional in-vivo designs, where one randomized subset of animals serves as a treatment group while a second subset serves as a control, are at a disadvantage instigated by greater subject-to-subject variability. Our goal was to provide a step-by-step methodological protocol for creating an alternative standardized, more economical, and transferable pre-clinical animal research model of excisional full-thickness wound healing following a simulated autologous tissue transfer which includes the primary ischemia, reperfusion, and secondary ischemia events with the latter mimicking flap salvage procedure.

RESULTS

Unlike in the most frequently used classical unilateral McFarlane's caudally based dorsal random pattern skin flap model, in the herein described bilateral epigastric fasciocutaneous advancement flap (BEFAF) model, one flap heals under normal and a contralateral flap-under perturbed conditions or both flaps heal under conditions that vary by one within-subjects factor. We discuss the advantages and limitations of the proposed experimental approach and, as a part of model validation, provide the examples of its use in laboratory rat (Rattus norvegicus) axial pattern flap healing studies.

CONCLUSIONS

This technically challenging but feasible reconstructive surgery model eliminates inter-subject variability, while concomitantly minimizing the number of animals needed to achieve adequate statistical power. BEFAFs may be used to investigate the spatiotemporal cellular and molecular responses to complex tissue injury, interventions simulating clinically relevant flap complications (e.g., vascular thrombosis) as well as prophylactic, therapeutic or surgical treatment (e.g., flap delay) strategies in the presence or absence of confounding risk factors (e.g., substance abuse, irradiation, diabetes) or favorable wound-healing promoting activities (e.g., exercise). Detailed visual instructions in BEFAF protocol may serve as an aid for teaching medical or academic researchers basic vascular microsurgery techniques that focus on precision, tremor management and magnification.

Fluctuations in Detection Indicators and Their Significance for the Diagnosis of Early Pressure Injury in Rat Models

PURPOSE

The aim of this study was to identify the most meaningful diagnostic indicator for distinguishing blanchable erythema (BE) and stage 1 pressure injury (early PI) in an in vivo (rat) model.

DESIGN

A prospective case-control design was used to complete a horizontal and vertical comparison of detection indicators during the process of fading of BE or the deterioration of early PI into ulcer in rat models.

MATERIALS AND SETTING

The sample comprised 5 hairless rats with 20 injuries, of which 10 were BE and the other 10 were early PI. Data were collected at Nagano College of Nursing in 2020 in Nagano, Japan.

METHODS

The BE and PI rat models were established by subjecting the dorsal skin of a hairless rat to compression between 2 neodymium magnets for 45 minutes and 3.45 hours, respectively. The affected skin was observed based on the following: (1) photography, (2) hardness, (3) temperature, (4) moisture, and (5) spectrophotometric (a* value and ultraviolet [UV] reflectance) measurements. All measurements of BE were performed at the beginning to 60 minutes after decompression, and those for early PI were performed until 48 hours after decompression.

RESULTS

Multiple BE factors, such as the degree of erythema (macroscopy and a* value), hardness, temperature, and moisture, were found to have unstable fluctuations. Only UV reflectance gradually decreased from 6 hours and decreased significantly at 48 hours after decompression (P = .001 vs 1 hour). In contrast to early PI, erythema in BE obviously faded within 10 minutes.

CONCLUSIONS

Study findings indicate that a continuous decrease in UV reflectance can reflect the worsening of hemorrhage in early (stage 1) PI. In contrast, other indicators including photography, skin hardness, temperature, and moisture fluctuated and did not prove predictive for PI progression. The obvious fading of erythema in BE a short time after decompression can be used for clinical observations.

Development of a mouse model of abdominal cutaneous flaps for breast reconstruction

Autologous tissue transfer, in addition to replacing tissue that was lost during injury or surgery, offers women an excellent option to improve cosmetic appearance and self-confidence following mastectomy due to breast cancer. However, flap necrosis is a complication in obese patients undergoing this procedure. We created a mouse model to study the flap-related complications that leads to decreased flap survival in autologous breast reconstruction.

Selective Percutaneous Desiccation of the Perforators with Radiofrequency for Strategic Transfer of Angiosomes in a Sequential Four-Territory Cutaneous Island Flap Model

BACKGROUND

Research in prevention of partial flap necrosis has recently concentrated on extending the safe length of a flap by ligating vessels of known territories. To advance this approach one step further, the authors decided to reveal the least invasive surgical strategy for transfer of angiosomes.

METHODS

The study was arranged into three experiments. In the first experiment (n = 17 rabbits), a cutaneous island flap model spanning four adjacent vascular territories was developed. In the second experiment (n = 15 rabbits), the flap model was used to test the possibility of desiccating those vessels supplying the angiosomes to be captured percutaneously with radiofrequency. The delay procedures were performed by means of minimal skin incisions, and the flaps were elevated after a 2-week delay period. In the third experiment, the effectiveness of selective interference of these pedicles was compared to minimize the number of target vessels for successful transfer of angiosomes.

RESULTS

The mean surviving area of the new flap model was 63 +/- 2 percent. The mean surviving flap area was 97 +/- 3 percent for the endoscopy equivalent technique and 94 +/- 4 percent for radiofrequency delay. The results were statistically insignificant between these two groups. In experiment 3, comparison of the results yielded a statistically insignificant difference for flap survival area among all four of the groups.

CONCLUSIONS

An alternative flap model is introduced for future investigation of the vascular delay process. Percutaneous desiccation of the perforators with radiofrequency was found to be a reliable method, and selective desiccation of the perforator(s) was as efficient as destruction of all vascular sources other than the pedicle.

Animal models in pressure ulcer research

BACKGROUND/OBJECTIVE

Research targeting the pathophysiology, prevention, and treatment of pressure ulcers (PrUs) continue to be a significant priority for clinical and basic science research. Spinal cord injury patients particularly benefit from PrU research, because the prevalence of chronic wounds in this category is increasing despite standardized medical care. Because of practical, ethical, and safety considerations, PrUs in the human environment are limited to studies involving patients with pre-existing ulcers. Therefore, we are limited in our basic knowledge pertaining to the development, progression, and healing environment in this devastating disease.

METHODS

This review provides a synopsis of literature and a discussion of techniques used to induce PrUs in animal models. The question of what animal model best mimics the human PrU environment has been a subject of debate by investigators, peer review panels, and editors. The similarities in wound development and healing in mammalian tissue make murine models a relevant model for understanding the causal factors as well as the wound healing elements. Although we are beginning to understand some of the mechanisms of PrU development, a key dilemma of what makes an apparently healthy tissue develop a PrU waits to be solved.

RESULTS AND CONCLUSIONS

No single method of induction and exploring PrUs in animals can address all the aspects of the pathology of chronic wounds. Each model has its particular strengths and weaknesses. Certain types of models can selectively identify specific aspects of wound development, quantify the extent of lesions, and assess outcomes from interventions. The appropriate interpretation of these methods is significant for proper study design, an understanding of the results, and extrapolation to clinical relevance.

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.

Comparison of two different delay procedures in a rat skin flap model

The overall objective of this study was to investigate how a strategic delay procedure could generate large flaps survival. On the basis of the vascular anatomy in 10 rats, a long three-territory skin flap spanning the length of the rat dorsum was designed. This flap was distally based on the deep circumflex iliac artery. The adjacent territories consisted of a large perforator of the posterior intercostal artery and the lateral thoracic artery in sequence. Two different vascular delay procedures were used and compared in nine animals. One dorsal midline incision was used to perform the two different delay procedures. The limited delay technique was performed by ligating a large cutaneous perforator of the posterior intercostal artery on one side of the rat. The extensive delay procedure was completed by ligating the cutaneous perforators of the posterior intercostal artery and the lateral thoracic artery on the other side of the rat. After a delay period of 10 days, the paired flaps were elevated, respectively, and sutured back in place. Seven days later, the area of viable skin flap was measured by the paper template technique. The animals were then killed, and the dorsal skin arteriograms were obtained by injecting a lead oxide mixture. Vascular changes of the paired flaps were assessed. In the extensive delay group, 100-percent survival was seen in four animals and distal partial necrosis was observed in five animals. The average survival area in the extensive delay group was 85.5 +/- 14.2 percent (mean +/- SD), whereas the flaps in limited delay group showed 100-percent survival in all animals (p < 0.05). In flaps that survived completely, the choke vessels among three vascular territories anastomosed throughout the flap. In the partially necrotic flaps, some choke and true anastomoses existed between the deep circumflex iliac and the posterior intercostal artery territories and the flap necrosis occurred in the third territory. This study suggests that the limited delay technique (ligation of one artery in the territory adjacent to the base of the flap) was the more effective delay procedure in the rat dorsal skin flap model.

Use of the Guinea Pig Flank Flap in Skin Flap Research

A variety of flaps in laboratory animals have been designed that propose to parallel the behavior of human skin under different experimental conditions. In the search for a readily available and affordable island skin flap model that combines reliable anatomy with a pedicle of substantial size, we have designed in the guinea pig a cutaneous flap based on the superficial circumflex iliac artery and vein. In 22 adult female Hartley guinea pigs, an 8 × 4 cm flank flap based on the superficial circumflex iliac pedicle was raised, and its characteristics were evaluated for applications to skin flap research. Dermofluorometric studies were performed that confirm the vascularity of this flap, and 100% survival of the flap was seen 5 days after surgery in all animals. Of particular benefit was the demonstration that both afferent and efferent blood samples can be taken from the pedicle directly, which allows for the direct quantification of plasma markers after physiologic insults to the skin flap, such as burn or ischemia. This anatomically reliable and easily dissected flap lends itself well to preliminary skin flap research and may contribute to standardization of a model for further studies examining the behavior of skin microcirculation under adverse physiologic conditions.