Pre-expanded perforator flaps, a combination of tissue expansion with perforator flaps, are emerging as another landmark of plastic surgery. This flap inherits the characteristics of both perforator flaps and expanded flaps, making it a highly versatile option in reconstructive surgery. However, the definition of the pre-expanded perforator flap and the impact of pre-expansion on the superficial angio-architecture remain controversial. In this article, the authors review current concepts including the mechanism of expansion and the resultant changes in the angio-architecture. The authors also review the previous studies and classifications of pre-expanded perforator flaps.
Key points
- •
Through previous studies on basic anatomy and prior clinical experience, pre-expanded perforator flaps have become a focus of ongoing research in plastic surgery because of advantages of both perforator flap and tissue expansion.
- •
The expansion process not only equals a flap delay procedure but also increases and enlarges the capillary vascular anastomosis, thereby increasing perfusion of the flap.
- •
Pre-expansion enables choke anastomoses to reform into real anastomoses, allowing a single perforator to carry 2 or more adjacent angiosomes, thereby increasing the flap survival area.
- •
Because of the different soft tissue planes that can be expanded, each with their respective blood supply, pre-expanded perforator flaps can repair soft tissue defects of various thicknesses.
Introduction
Tissue expansion has allowed plastic surgeons to recruit greater amounts of soft tissue for repairing various defects throughout the body. This technique has proved invaluable in plastic surgery and can be seen as a reconstructive milestone in the history of plastic surgery.
When Neumen first reported the clinical application of rubber balloons as an implant in the 1950s, he used the term “skin expansion,” describing the concept that “skin and subcutaneous tissue are capable of being expanded and it is possible to achieve such expansion in regions where it may be needed for clinical use.” However, the first modern clinical application of the soft tissue expansion technique did not emerge until Radovan applied the technique for breast reconstruction in 1976. In the same period of time, Zhang and Jin first used tissue expanders underneath the skin to reconstruct postburn malformations and achieved good clinical outcome in P.R. China in 1985. Vistnes thought highly of tissue expansion and its astounding results and equated such a technique to microsurgery as one of the landmark techniques in reconstructive surgery. Since then, there has been a tremendous growth of basic science research on the biochemistry, biomechanics, hemodynamics, and molecular biology of tissue expansion. Studies have paid especially close attention to investigating changes in the regional angio-architecture and survival of the donor tissues after flap expansion. Based on these studies, tissue expansion techniques have developed to include expanded random flaps, expanded axial flaps, and expanded free flaps.
The clinical application of the perforator flap by Kroll and Rosenfield showed reduction in donor site deformity with obvious improvements in the repair. These changes transitioned soft tissue flaps from crude to refined. Tissue reconstruction no longer needed to simply cover the defect. Plastic surgeons gradually could restore both form and function. The “Gent” Consensus on Perforator Flap Terminology: Preliminary Definitions was published by a group of internationally renowned plastic surgeons in 2003. This article acknowledged the impact of perforator flaps and the increasing value within the international plastic surgery community.
Along with such profound studies on perforators, the combination of the tissue expansion technique with perforator flaps coincidentally emerged at the right time. Tsai first used such an innovative technique in reconstruction after the release of burn scar contracture. As the combination of tissue expansion with perforator flaps had been applied by plastic surgeons worldwide for various clinical applications, this marked the naissance of the pre-expanded perforator flap.
In this article, the authors review the changes to the superficial vascular system after tissue expansion and the proposed mechanism as well as the clinical values and classifications of the pre-expanded perforator flap, based on the updated knowledge on perforator flaps and tissue expansions.
Introduction
Tissue expansion has allowed plastic surgeons to recruit greater amounts of soft tissue for repairing various defects throughout the body. This technique has proved invaluable in plastic surgery and can be seen as a reconstructive milestone in the history of plastic surgery.
When Neumen first reported the clinical application of rubber balloons as an implant in the 1950s, he used the term “skin expansion,” describing the concept that “skin and subcutaneous tissue are capable of being expanded and it is possible to achieve such expansion in regions where it may be needed for clinical use.” However, the first modern clinical application of the soft tissue expansion technique did not emerge until Radovan applied the technique for breast reconstruction in 1976. In the same period of time, Zhang and Jin first used tissue expanders underneath the skin to reconstruct postburn malformations and achieved good clinical outcome in P.R. China in 1985. Vistnes thought highly of tissue expansion and its astounding results and equated such a technique to microsurgery as one of the landmark techniques in reconstructive surgery. Since then, there has been a tremendous growth of basic science research on the biochemistry, biomechanics, hemodynamics, and molecular biology of tissue expansion. Studies have paid especially close attention to investigating changes in the regional angio-architecture and survival of the donor tissues after flap expansion. Based on these studies, tissue expansion techniques have developed to include expanded random flaps, expanded axial flaps, and expanded free flaps.
The clinical application of the perforator flap by Kroll and Rosenfield showed reduction in donor site deformity with obvious improvements in the repair. These changes transitioned soft tissue flaps from crude to refined. Tissue reconstruction no longer needed to simply cover the defect. Plastic surgeons gradually could restore both form and function. The “Gent” Consensus on Perforator Flap Terminology: Preliminary Definitions was published by a group of internationally renowned plastic surgeons in 2003. This article acknowledged the impact of perforator flaps and the increasing value within the international plastic surgery community.
Along with such profound studies on perforators, the combination of the tissue expansion technique with perforator flaps coincidentally emerged at the right time. Tsai first used such an innovative technique in reconstruction after the release of burn scar contracture. As the combination of tissue expansion with perforator flaps had been applied by plastic surgeons worldwide for various clinical applications, this marked the naissance of the pre-expanded perforator flap.
In this article, the authors review the changes to the superficial vascular system after tissue expansion and the proposed mechanism as well as the clinical values and classifications of the pre-expanded perforator flap, based on the updated knowledge on perforator flaps and tissue expansions.
Updated knowledge on perforator flaps
In 1987, Taylor and Palmer used radiographic investigations and dye injections in several fresh cadavers to study the anatomic territory of source arteries in the skin and deep tissues; 374 major perforators were identified resulting in the concept of angiosomes.
Taylor and Palmer’s angiosome theory indicated that the superficial vessels do not end in the cutaneous layer of tissue but rather form a vascular network across the body. Between adjacent angiosomes are 2 types of anastomosis: true vessels and choke vessels ( Fig. 1 ). In between each territory are choke zones that serve as a dividing line. The traditional axial flap (including the perforator flap) is equivalent to having one dominant vessel supplying the vascular flap. A random-based flap consists of several small, nondominant vascular plexuses that supply the flap. However, it has been shown that the vascular territory of axial-based flaps is often supplemented by adjacent smaller, nondominant vascular perforators. This finding supports the concept that the safe clinical territory of a cutaneous perforator extends beyond the anatomic territory of that perforator to include the anatomic territory of the next adjacent cutaneous perforator, situated radially in any direction. Based on Taylor and Palmer’s studies, the flap survival area depends on the spacing between the territories of each perforator flap. The dominant flap can expand into neighboring nondominant territory flap areas because of the changes of the choke vessels between the perforator territory flaps developing into true vessel anastomosis ( Fig. 2 ).
Expanding on the angiosomes theory, Saint-Cyr and colleagues further extend the angiosome theory to the term perforasome based on their anatomic studies in 2009. This theory states each perforator holds a unique vascular territory. The most important idea is that each perforasome is linked with adjacent perforasomes by means of 2 main mechanisms that include both direct and indirect linking vessels, the large vessels named direct linking vessels and indirect linking vessels linking perforasomes through the subdermal plexus. Meanwhile, mass vascularity of a perforator found adjacent to an articulation is directed away from that same articulation, whereas perforators found at a midpoint between 2 articulations or at the midpoint in the trunk have a multidirectional flow distribution. Therefore, perforasomes have the following characteristics: adjacent perforating branches of the blood supply to the region have connections through direct and indirect links and through different directions of communication between the different branches ( Fig. 3 ).
Taylor and colleagues performed angiography on human skin to better describe the vascular architecture. The arteries were studied in detail, according to the system proposed by the vascular territories concept. (Angiosomes were to define the characteristics and laws of stereoscopic 3-dimensional [3D] distribution of blood vessels.) Statistics of the perforating skin vessels of the average human body revealed average diameters of 0.5 mm or greater; 374 identified vessels can be distributed to form nearly 40 perforator vessel flaps. These vascular findings (referred vascular distribution areas) promote a novel approach to identifying potentially new flap donor sites. It also paves the way for a new generation of surgical procedures based on perforator flaps and promotes improvements in the traditional way flap reconstruction is performed. In 2008, Tang and colleagues proposed an application of 3D-Doctor, Mimics, Amira, and other 3D reconstruction software that could be succeeded traditional computed tomography (CT)–guided imaging of perforator flaps by way of 3D visualization. Over the same period, Masia and colleagues and Alonso-Burgos and colleagues reported using CT-guided 3D imaging software in preoperative planning for deep inferior epigastric artery perforator flap reconstruction. These novel surgical planning tools have further accelerated perforator flaps into the digital era, allowing for enhanced visualization of the surgical anatomy with direct translation for clinical application of perforator flap design.
Contemporary concepts of pre-expanded perforator flaps
Kroll and Rosenfield first introduced the perforator in 1988. Soon after, Koshima and Soeda described the rectus abdominis musculocutaneous perforator flap in 1989. Since the late 1980s, perforator flaps have become widely used in breast reconstruction. However, there was confusion regarding perforator flaps in definition and nomenclature; this caused difficulties when surgeons attempted to communicate their results or surgical techniques. In 2003, the Gent consensus was reached, creating standardized definitions and agreed rules on terminology and nomenclature regarding perforator flaps. Thus, a perforator flap is defined as a flap that only consists of skin and/or subcutaneous fat. The vessels that proved blood supply to the flap are isolated perforators.
Sensibly then, the pre-expanded perforator flap refers to the creation of a perforator flap that has greater soft tissue coverage by using the technique of tissue expansion. Expanders are placed in the subcutaneous layer and under the perforator in order to recruit skin and/or soft tissue overlying the flap. Current clinical applications of pre-expanded flaps include expanded local flap, expanded axial flap, expanded free flap, expanded superthin flap, and expanded prefabricated flap. Although all these flaps are applied as perforator flaps, their classification remains ambiguous. However, for a pre-expanded perforator flap, the effect of tissue expansion on improvement of blood supply to the flap is more important than its classification.
Previous studies on pre-expanded skin flaps
Comparison of Flap Expansion with Flap Delay
In the early literature, most investigators regarded the effect caused by tissue expansion as analogous to the delay phenomenon. However, current evidence shows that the result of expansion may surpass the delay phenomenon. Some studies indicate that expansion can also increase the ratio of length to width in random-pattern skin flaps as a result of the augmentation of blood vessels and the enlargement of vessel caliber along the long axis of the flap. Saxby also found that the survival lengths of expanded flaps were approximately 50% greater than those of delayed controls.
The delay phenomenon in expanded flaps occurs with changes of the vascular structure in the dermal layer. Leighton and colleagues found that the superficial vascular networks enlarge following expansion. The study described prominent neovascularization within the papillary dermis and capsular layers during expansion of their musculocutaneous flaps. Furthermore, microscopic observations of expanded skin revealed increases in capillary count and significant increases in capillary blood flow within the dermal blood vessels. Although their studies focused on axial flaps, the vasculature is the same in perforator flaps. Therefore, pre-expanded perforator flaps can be used to cover any soft tissue defect without the need of muscle transplantation or reinnervation.
Different Ways of Tissue Expansion
Different ways of tissue expansion induce different patterns of angiogenesis. Marks and colleagues found that rapid expansion led to augmentation of capillary blood flow in expanded skin and enhanced preservation of capillary flow. Moreover, repeated rapid expansion may be better than rapid expansion. Liu and colleagues found that repeated rapid expansions can effectively improve vascular density in expanded skin flaps and is superior to rapid expansion or conventional expansion technique. Thus, the researchers recommended repeated rapid expansion because of its efficacy in promoting vascularization of the flap and the added benefit of shortening the period of treatment needed. Moreover, they recommended a 4-week period after expansion so as to increase the area of expanded skin. Zeng and colleagues also substantiated these recommendations by performing biomechanical studies. However, based on the authors’ clinical experience, they think that normal expansion techniques can also achieve an ideal result when developing superthin skin perforator flaps.
Role of Formed Capsule
The capsule that forms around the expander during tissue expansion remains a controversial topic, specifically, whether it should be excised or not during the subsequent procedure. One study shows that the immediate retraction rate reduces greatly after capsule excision. Thus, the biomechanics of the expanded tissue can better approximate normal skin. However, Yang argues that it is necessary to keep the capsule when elevating the flap because vessel density between expanded skin and expanded capsule is conspicuous. Therefore, the associated capsule plays a crucial role in improving the survival rate of expanded skin flaps; the authors routinely keep the capsule with the flap while elevating a pre-expanded superthin skin perforator flap because the capsule developed during the initial expansion may play a role to improve survival of the distal flap for reconstruction.
Cross-Area of Blood Supply
In the authors’ experimental study on mini-pigs in 2005, using angiography to study the deep iliac circumflex artery and superior epigastric artery, their research showed that in the tissue expansion group, target vessels are fully perfused with abundant anastomoses of considerable size and caliber. This finding is compared with the delay group, which had relatively less anastomoses, smaller calibers, and smaller territory perfused, compared with the control group, with hardly any visualized target vessels. The flap survival rate in the expanded group was significantly higher than the control group in experiment A. The survival rate in the expanded group was also significantly higher than the delay group in experiment B ( Fig. 4 ).
