Augmentation of skeletal muscle flap survival using platelet derived growth factor

Venous component in scar penetrating neovascularisation

BACKGROUND

The impact of old scar tissue on the venous anatomy of a flap's pedicle is an important question in reconstructive surgery. This study tried to investigate the venous component in scar penetrating neovascularisation.

METHODS

Fifty Sprague-Dawley rats were used in this experimental study. Two experimental groups were designed. In the first group, incisions were performed over the epigastric flap pedicles. In the second group, 1 cm wide segments were excised over the pedicles. Ten weeks after the initial operations, angiographies and histological examinations were performed. A control group was used to demonstrate the normal arterial and venous anatomy of the pedicle.

RESULTS

Arterial angiographies revealed that axial pattern arteries were visible in the incision group as opposed to the excision group. Although venous angiographies showed that there were more venous capillary formations in the incision group, none of the experimental groups had regenerated a vein with an axial pattern. Histological examinations revealed that venous vessel formations were significantly less in the distal samples of the experimental groups when compared to the control group (p < 0.05).

CONCLUSIONS

In this study, it has been observed that arterial pedicles do regenerate over old incision scars as opposed to veins. In the excision scars neither arterial or venous restoration of the axial pedicle was possible. In these cases, only a random type of limited circulation was restored.

Effect of preoperative subcutaneous platelet-rich plasma and fibrin glue application on skin flap survival

BACKGROUND

The aim of this study was to compare the effects of preoperative subcutaneous platelet-rich plasma and fibrin glue administration on skin flap survival.

METHODS

One week before surgery; saline, platelet-rich plasma, fibrin glue, and thrombin solutions were applied under rat skin flap areas in Groups I, II, III, and IV, respectively. Unipedicled epigastric flaps were elevated in the first three groups but could not be elevated in Group IV because of preoperative abdominal skin necrosis. Necrotic area measurements, microangiography, and histological and immunohistochemical evaluations were performed.

RESULTS

Platelet-rich plasma reduced the percentage of necrotic area when compared to other groups. Histologically and microangiographically an increased number of arterioles were observed in the platelet-rich plasma group. Thrombin (when used alone) caused abdominal skin necrosis. Increased expression of VEGF and PDGF was found in all platelet-rich plasma-treated flaps. There was no significant difference between groups with respect to TGF-β3 staining intensity.

CONCLUSION

In this study preoperative administration of platelet-rich plasma mimicked the pharmacological delay effect and enhanced flap survival. Individual use of thrombin was found to be unsuitable in flap surgery.

LEVEL OF EVIDENCE I

This journal requires that authors assign a level of evidence to each article.

Effect of topical angiotensin II on prelaminated flaps in rats and evaluation of angiogenesis with an immunohistochemical marker

The effects of a single topical dose of angiotensin II (AII) on prelamination of flaps were investigated in rats using an immunohistochemical marker. Ninety rats were randomly divided into three groups (n = 30 in each). The control group were given nothing; the vehicle group were given only carboxymethyl cellulose, and the treatment group were given topical AII with carboxymethyl cellulose between the flap and the skin graft. According to the day of evaluation of vascularisation, each group was randomly divided into three sub-groups on days 4, 7, and 14 (n = 10 in each). Paraffin sections of the tissues were cut at the flap-graft interface and stained immunohistochemically with factor VIII-related antigen (FVIIIRAg). Capillaries and venules that stained were counted. The number of vessels in the groups on day 4 were similar, but by day 7 the number of vessels was significantly greater in the treatment group than the other two. The number of vessels in the treatment group on day 14 was greater than in the other two groups, but not significantly so. We conclude that a single topical dose of AII increases the vascularisation at the flap and skin graft interface by angiogenesis.

Vascular Delay Revisited

The technique of vascular delay has been used by plastic surgeons for nearly 500 years and has proven useful for reliably transferring tissue and allowing for a greater volume of tissue to be reliably harvested. Delay procedures are an essential plastic surgical tool for a variety of aesthetic and reconstructive procedures. Despite the widespread use of vascular delay procedures, the mechanism by which this phenomenon occurs remains unclear. A number of groups have exhaustively examined microvascular changes that occur during vascular delay. Theories have been proposed ranging from the dilation of choke vessels to changes in metabolism and new blood vessel formation. Inherent in these theories is the concept that ischemia is able to act as the primary stimulus for vascular changes. The purpose of this review is to revisit the theories proposed to underlie the delay phenomenon in light of recent advances in vascular biology. In particular, the participation of bone marrow-derived endothelial progenitor cells in the delay phenomenon is explored. Greater understanding of the role these cells play in new blood vessel formation will be of considerable clinical benefit to high-risk patients in future applications of delay procedures.

Improved survival of ischemic cutaneous and musculocutaneous flaps after vascular endothelial growth factor gene transfer using adeno-associated virus vectors

A major challenge in reconstructive surgery is flap ischemia, which might benefit from induction of therapeutic angiogenesis. Here we demonstrate the effect of an adeno-associated virus (AAV) vector delivering vascular endothelial growth factor (VEGF)165 in two widely recognized in vivo flap models. For the epigastric flap model, animals were injected subcutaneously with 1.5 x 10(11) particles of AAV-VEGF at day 0, 7, or 14 before flap dissection. In the transverse rectus abdominis musculocutaneous flap model, AAV-VEGF was injected intramuscularly. The delivery of AAV-VEGF significantly improved flap survival in both models, reducing necrosis in all treatment groups compared to controls. The most notable results were obtained by administering the vector 14 days before flap dissection. In the transverse rectus abdominis musculocutaneous flap model, AAV-VEGF reduced the necrotic area by >50% at 1 week after surgery, with a highly significant improvement in the healing process throughout the following 2 weeks. The therapeutic effect of AAV-VEGF on flap survival was confirmed by histological evidence of neoangiogenesis in the formation of large numbers of CD31-positive capillaries and alpha-smooth muscle actin-positive arteriolae, particularly evident at the border between viable and necrotic tissue. These results underscore the efficacy of VEGF-induced neovascularization for the prevention of tissue ischemia and the improvement of flap survival in reconstructive surgery.

Growth factors and flap survival

Growth factors are members of a large functional group of polypeptide regulatory molecules that influence the biological activities of responsive cells. In the last decade, the use of a variety of growth factors as therapeutic agents to improve wound healing and the viability of ischemic skin flaps has aroused considerable interest. Here, we review the literature concerning the regulation of growth factors in a flap, the role of angiogenesis in flap survival, the effect of growth factors on the metabolism of a flap, and angiogenesis in flap prefabrication and maturation. The potential application of growth factors in gene therapies is also reviewed.

Vascular endothelium growth factor, surgical delay, and skin flap survival

OBJECTIVE

Cytokines may be a mechanism by which surgical delay can increase flap survival. We previously found that preoperative vascular endothelium growth factor (VEGF) administration in the rat transverse rectus abdominis myocutaneous (TRAM) flap could improve skin paddle survival. In this study, we used partial elevation of the rat TRAM flap as a surgical delay to assess endogenous cytokine expression and tissue survival comparable to undelayed TRAM flaps.

METHODS

In Part I, TRAM flaps underwent surgical delay procedures; 7 days later, the flaps were completely elevated and reinset. At the same time, other flaps were raised and reinset without delay. Skin paddle survival in both groups was evaluated at 7 days. In Part II, skin biopsies from TRAM zones I to IV were taken at the time of delay and at intervals of 12, 24, 48, and 72 hours. Specimens were assessed for selected cytokine gene expression by reverse transcription-polymerase chain reaction analysis (TR-PCR).

RESULTS

Surgical delay significantly (P < 0.001) increased skin paddle survival in the delayed TRAM flaps (16.14 +/- 1.53 cm, 81.9%) compared with undelayed flaps (7.68 +/- 3.16 cm, 40.9%). TGF-beta and PDGF expressions were not changed by surgical delay, but basic fibroblast growth factor (bFGF) and VEGF expressions increased significantly (P < 0.05 and P < 0.01) after delay.

CONCLUSIONS

In the rat TRAM model, surgical delay resulted in increased VEGF expression and increased skin paddle survival. These results correlate with previous studies showing the preoperative injection of VEGF increases skin paddle survival. VEGF may be an important element in the delay phenomenon and may be an agent for pharmacological delay.

Gene therapy in flap survival

Growth factors are members of a large functional group of polypeptide regulatory molecules that exert a powerful influence on all phases of wound healing and repair through interactions with specific cell surface receptors. The use of growth factors to improve wound healing and the viability of ischemic skin flaps has been well-documented throughout the last decade. In this article, we review the literature concerning the use gene therapy in flap survival, including the various methods employed to transplant plasmids or viruses capable of coding and producing growth factors in ischemic tissue.

Effect of vascular endothelial growth factor-induced angiogenesis on TRAM flap harvesting after abdominoplasty

In this study, the effect of intramuscular injection of human vascular endothelial growth factor (hVEGF) on neovascularization following abdominoplasty was investigated. Twenty-four Sprague-Dawley rats were divided into four groups (n = 6). Two control groups and two experimental groups were established. Abdominoplasty was performed in all rats, with division of all the perforator vessels. In the control groups, normal saline was injected into the rectus abdominis muscle, and in the experimental groups, 100 microg of VEGF and normal saline were injected into the rectus muscle. A transverse rectus abdominis musculocutaneous (TRAM) flap was harvested on day 20 and day 40 in both the control and experimental groups. The range of viability of the TRAM flap was, respectively, 0 to 20 percent (mean, 6.7 percent) and 0 to 25 percent (mean, 14.2 percent) in both short-term and long-term control groups (no VEGF injected). The study (VEGF) group demonstrated a viability of 50 to 80 percent (mean, 70 percent) for the short-term group and 50 to 85 percent (mean, 72.5 percent) in the long-term group. No wound infection was documented, and there were no deaths during the study period. There was no statistically significant difference between the short-term and long-term divisions of the groups (p < 0.01); however, significant differences were observed between the control and experimental groups (p < 0.01). The authors concluded that VEGF injection after abdominoplasty improved the percentage of TRAM flap viability. This method of delay/revascularization could be used for the difficult problem of flap viability following abdominoplasty and for high-risk patients.

Effects of the abdominal midline incision on the survival of the transverse rectus abdominis musculocutaneous flap in rat model

The transverse rectus abdominis musculocutaneous (TRAM) flap, as the standard for breast reconstruction, can be performed in selected patients with operation scars in the abdomen. It is questioned why the unilateral TRAM flaps raised from the abdomen with scars seem to have more blood supply to the periphery. The effect of the abdominal midline incision on the survival of the TRAM flap was studied with the rat model. The survival of the inferiorly based unilateral TRAM flap was compared between a control group and three experimental groups in which initial abdominal midline incision was made 1, 2, or 4 weeks before TRAM flap elevation. The control group had a mean survival of 47.05 +/- 4.52% of their original flap surface area. The viabilities of the other groups were 72.19 +/- 11.05, 76.96 +/- 7.79, 90.26 +/- 3.67%, respectively. Results from all three groups were significantly higher than that of the control group. In the microangiogram of the TRAM flap, the main pedicle (deep epigastric system) and muscle perforators remained unchanged, but the subdermal plexus of the abdominal wall showed increase of size and density after incision. Histological examination also revealed corresponding findings. A midline incision in the abdomen, which was made at 1 or more weeks before unilateral TRAM flap formation, was found to improve the survival of the flap. These data may be explained by increase in the size and density of the subdermal plexus, which delivers the blood flow from the muscle perforators to the expanded area of abdominal wall. Therefore, the process of making the abdominal midline incision can be regarded as a minimal form of a prefabrication procedure, which is one of the well-known delay procedures.

A review of therapeutic angiogenesis and consideration of its potential applications to plastic and reconstructive surgery

The use of exogenous agents to stimulate the growth of new blood vessels into ischaemic tissue is a potentially revolutionary therapy in a wide variety of clinical specialties. Therapeutic angiogenesis research has been mostly confined to ischaemia of the heart and the lower limb. There has been relatively little research into the potential applications of the technique to plastic, reconstructive and burns surgery. In this paper, relevant published work is reviewed and potential applications of therapeutic angiogenesis to our specialty are considered.

Vascular delay and administration of basic fibroblast growth factor augment latissimus dorsi muscle flap perfusion and function

Ischemia of the distal latissimus dorsi muscle flap occurs when the entire muscle is acutely elevated. Although this level of ischemia may not be critical if the muscle is to be used as a conventional muscle flap, the ischemia causes decreased distal muscle function if it is used for dynamic muscle flap transfer. This experiment was designed to determine whether or not the administration of exogenous basic fibroblast growth factor (bFGF), combined with a sublethal ischemic insult (i.e., vascular delay), would further augment muscle perfusion and function. Both latissimus dorsi muscles of nine canines were subjected to a bipedicle vascular delay procedure immediately followed by thoracodorsal intraarterial injection of 100 microg of bFGF on one side and by intraarterial injection of vehicle on the other. Ten days later, both latissimus dorsi muscles were raised as thoracodorsally based island flaps, with perfusion determined by laser-Doppler fluximetry. The muscles were wrapped around silicone chambers, simulating cardiomyoplasty, and stimulating electrodes were placed around each thoracodorsal nerve. The muscles were then subjected to an experimental protocol to determine muscle contractile function. At the end of the experiment, latissimus dorsi muscle biopsies were obtained for measurement of bFGF expression. The results demonstrated that the administration of 100 microg of bFGF immediately after the vascular delay procedure increases expression of native bFGF. In the distal and middle muscle segments, it also significantly increased muscle perfusion by approximately 20 percent and fatigue resistance by approximately 300 percent. The administration of growth factors may serve as an important adjuvant to surgical procedures using dynamic muscle flap transfers.