Pedicle perforator flaps and keystone perforator island flaps are additional tools for reconstructive surgeons. Advances in understanding of vascular anatomy, the dynamic nature of perforator perfusion, inter-perforator flow and the hot-spot principle have led to reconstructive techniques that allow innovative autologous tissue transfer while limiting donor site morbidity. Further modifications of the pedicle perforator flap have led to a multitude of freestyle pedicle perforator flap options, as well as freestyle free flaps for soft tissue reconstruction. Modifications in the keystone perforator island flap have increased the degrees of freedom for soft tissue coverage of large defects, with reliable and aesthetically pleasing results.
Key points
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The increase in knowledge of vascular anatomy, including the concept of the perforasome theory and perforator hot-spot versus cold-spot anatomy, has led to significant advances in reconstructive options.
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Pedicle perforator flap (PPF)–based reconstruction benefits patients by using autologous tissue for reconstruction and decreases operative morbidity by limiting transfer of tissue on perforators.
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Freestyle PPF allows greater degrees of freedom in operative planning, because flaps can be based on any dominant perforator.
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Keystone perforator island flap is a multiperforator advancement flap based on musculocutaneous or fasciocutaneous perforators with high rates of flap survival, decreased donor site morbidity and pain, and quick patient recovery.
Introduction
Initial descriptions of perforator flaps in 1989 by Koshima and Soeda, by using a musculocutaneous flap with an inferior epigastric artery–based skin island for reconstruction of defects involving the floor of mouth and groin, have led to significant additional advancements in the understanding of perforator flaps and vascular anatomy. Kroll and Rosenfield reported that perforator flaps had vascular reliability comparable with musculocutaneous flaps, but limited donor site morbidity by avoiding muscle harvest. The transfer of tissues therefore is not limited by the requirement to include muscle or underlying deep fascia for adequate tissue perfusion. Milton showed that the inclusion of a pedicle with a large vessel was critical for flap survival, and also dictated the viable length of harvest for islanded flaps.
Further modifications of the perforator flap led to the advent of the propeller flaps, first introduced in 1991 by Hyakusoku and colleagues, with later modifications by Hallock and Teo. Propeller flaps allow significant tissue reconstruction with ideal like-for-like tissue, and maintain similar complication rates to free flap reconstruction. Recent advances in the understanding of vascular anatomy have led to significant advancements and freedom in perforator-based reconstruction. Taylor and Palmer introduced the angiosome concept, which was further detailed in many additional studies evaluating the static vascular territories of every source vessel and their perforators. Further anatomic studies by Saint-Cyr and colleagues and other investigators introduced the perforasome concept of distinct vascular territories of individual perforators, which are dynamic and have significant interactions with adjacent perforating vessels or perforasomes.
The keystone perforator island flap (KPIF) is a versatile flap that was originally described by Behan for reconstruction of defects after excision of skin cancer, and has since been used for the reconstruction of defects located on the head and neck, trunk, and extremities. Modifications in planning, design, and execution of the KPIF by relying on a sound understanding of vascular anatomy and the perforasome theory by Saint-Cyr and colleagues have allowed large defect reconstruction after tumor resection, with high rates of flap survival, low risk of significant complications, decreased pain, and quicker postoperative recovery.
Introduction
Initial descriptions of perforator flaps in 1989 by Koshima and Soeda, by using a musculocutaneous flap with an inferior epigastric artery–based skin island for reconstruction of defects involving the floor of mouth and groin, have led to significant additional advancements in the understanding of perforator flaps and vascular anatomy. Kroll and Rosenfield reported that perforator flaps had vascular reliability comparable with musculocutaneous flaps, but limited donor site morbidity by avoiding muscle harvest. The transfer of tissues therefore is not limited by the requirement to include muscle or underlying deep fascia for adequate tissue perfusion. Milton showed that the inclusion of a pedicle with a large vessel was critical for flap survival, and also dictated the viable length of harvest for islanded flaps.
Further modifications of the perforator flap led to the advent of the propeller flaps, first introduced in 1991 by Hyakusoku and colleagues, with later modifications by Hallock and Teo. Propeller flaps allow significant tissue reconstruction with ideal like-for-like tissue, and maintain similar complication rates to free flap reconstruction. Recent advances in the understanding of vascular anatomy have led to significant advancements and freedom in perforator-based reconstruction. Taylor and Palmer introduced the angiosome concept, which was further detailed in many additional studies evaluating the static vascular territories of every source vessel and their perforators. Further anatomic studies by Saint-Cyr and colleagues and other investigators introduced the perforasome concept of distinct vascular territories of individual perforators, which are dynamic and have significant interactions with adjacent perforating vessels or perforasomes.
The keystone perforator island flap (KPIF) is a versatile flap that was originally described by Behan for reconstruction of defects after excision of skin cancer, and has since been used for the reconstruction of defects located on the head and neck, trunk, and extremities. Modifications in planning, design, and execution of the KPIF by relying on a sound understanding of vascular anatomy and the perforasome theory by Saint-Cyr and colleagues have allowed large defect reconstruction after tumor resection, with high rates of flap survival, low risk of significant complications, decreased pain, and quicker postoperative recovery.
Perforasome principles
The ability of a single arterial perforator to adequately vascularize large volumes of soft tissue for reconstruction can only be understood with a comprehensive understanding of the perforasome theory. A perforasome is described as the unique vascular territory of a single arterial perforator from an underlying source vessel. Four major principles elucidate the ability of a single perforator to sustain a large volume of soft tissue, and the consistent preferential direction of vascular flow.
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Perforasomes are linked with adjacent perforasomes by direct and indirect linking vessels ( Fig. 1 ). Direct linking vessels are larger vessels that directly connect one perforator to another in the suprafascial plexus, whereas indirect perforators connect one perforator to another through the subdermal plexus. In addition, there are communicating branches that connect direct linking vessels to indirect linking vessels. Interperforator flow is bidirectional, with directionality of flow dependent on perforator perfusion pressures. With adequate perfusion pressure, a single perforator can vascularize multiple perforasomes via interperforator flow.
Fig. 1
( A , B ) Linking vessels, direct and indirect.
( Courtesy of Alexandra B. Hernandez, M.A. of Gory Details Illustration; with permission.)
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Design of the flap and orientation of the skin paddle should be in the same direction as the linking vessels, which are axial in the extremities and perpendicular to the midline in the trunk. Linking vessels allow for interperforator communication between perforators from the same underlying source arteries and with perforators of adjacent source arteries ( Fig. 2 ).
Fig. 2
Linking vessels parallel to long axis of limb and parallel to source artery.
- 3.
Perforators from the same source artery are preferentially filled by interperforator flow. In addition, if a source artery has minimal perforating vessels along its vascular path, there is a decrease in the axial pattern of its vascular distribution because there are fewer interperforator linking vessels ( Fig. 3 ).
Fig. 3
Preferential filling of interperforator flow within same source artery.
( Courtesy of Alexandra B. Hernandez, M.A. of Gory Details Illustration; with permission.)
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Directionality of a perforator can be determined based on its proximity to an articulation. Perforators found adjacent to an articulation have preferential directionality away from the articulation, whereas perforators between 2 articulations or at the midpoint of the trunk have multidirectional flow ( Fig. 4 ).
Fig. 4
Perforator flow bidirectional for midpoint perforators and away from articulations for eccentric perforators.
( Courtesy of Alexandra B. Hernandez, M.A. of Gory Details Illustration; with permission.)
These principles explain how large volumes of soft tissue can be harvested, because hyperperfusion of a single perforator can capture multiple adjacent perforasomes, with preferential flow in the direction of the linking vessels, reflecting the path of the underlying source artery.
Perforator hot spot versus cold spot
There are nearly 400 perforators in the body, on each of which a pedicle-based flap can be raised, allowing multiple alternative reconstructive options. Perforator flaps have been described for reconstruction of the breast, head and neck, and extremities. The perforators are not distributed evenly, because the body has areas of higher perforator density, called hot spots, and areas of lower perforator density, called cold spots ( Fig. 5 ). Hot spots are consistently found in the same areas of the body. In the extremities, they are found typically adjacent to articulations and midway between 2 articulations, whereas in the trunk they are found parallel to the anterior and posterior midline, and midaxillary regions. Knowledge of hot-spot territories allows optimal surgical planning of the flap, and permits quicker surgical dissection in cold spots.
Perfusion principles: perforator location and angle of perfusion
The volume of soft tissue that can safely be harvested in a pedicle perforator flap (PPF) depends on the ability of the dominant perforator to adequately perfuse the entire flap. Principles that aid in optimizing the vascularity of a flap include the relative position of the dominant perforator within the flap, and the angle of perfusion. Designing flaps with the primary perforating vessel positioned centrally allows for greater interperforator flow by preserving the linking vessels (direct and indirect) and the communicating vessels, resulting in a greater number of adjacent perforasomes that are vascularized. Eccentric positioning of a perforator decreases the volume of tissue that can safely be harvested. However, if great care is taken to ensure that the linking vessels are parallel to the long axis of the designed flap, complications of flap loss can be avoided or minimized ( Fig. 6 ).
The angle of perfusion of a perforator is defined as the angle of vascular perfusion flowing away from the perforator and confined by the mechanical borders of the flap. The angle is measured at the proximal aspect of the flap. In a cadaveric study of anterolateral thigh flaps, area of perfusion and percentage of flap perfusion were evaluated based on differing angles of perfusion, by using computed tomography (CT) angiography. Decreasing the angle of perfusion resulted in a significant decrease in the volume and percentage of flap perfusion. An acute angle of perfusion (60°) is thought to be disruptive of interperforator flow by failing to incorporate linking vessels between adjacent perforators, and thus decreasing flap perfusion. The flap vascularization by the dominant perforator can be optimized by positioning the perforator in the central portion of the flap and by avoiding an acute angle of perfusion at the proximal aspect of the flap. These modifications allow for increased interperforator flow by incorporating critical linking vessels, resulting in a robustly perfused flap.
Benefits of perforator flaps
PPF allow complex locoregional reconstruction while avoiding microsurgical free-flap reconstruction and monitoring. The main advantages of perforator flaps include sparing of underlying muscle, decreased donor site morbidity, decreased operative times, and improved aesthetic outcome by supplying like with like for optimal texture, thickness, and color match ( Fig. 7 ). The KPIF is a single flap based on multiple perforators that has shown excellent reconstructive outcomes for large defects while avoiding free-flap reconstruction and allowing shorter operative times, fairly pain-free postoperative course, and shorter duration of hospitalization, and is ideal for patients with multiple comorbidities who are unable to undergo prolonged complex reconstructive procedures ( Fig. 8 ).
Patient selection and preoperative planning
Each patient presents a unique challenge to the reconstructive surgeon because each patient introduces individual-specific comorbidities, including prior trauma, reconstructive surgery, prior irradiation, and smoking, all of which affect the vascularity and mobility of the adjacent tissue. When evaluating a patient for reconstruction with a KPIF or PPF, it is critical to evaluate the defect and the quality of the adjacent tissue, particularly noting the soft tissue laxity. Preoperative imaging is not routinely indicated for identification of perforators, because sound knowledge of perforator location based on the hot-spot principle, in conjunction with Doppler evaluation of the adjacent tissue, is sufficient ( Fig. 9 ). Radiographic studies that are preoperatively obtained by the oncologic team for evaluation of tumor invasiveness, including CT or MRI, can help identify large perforators in the vicinity of the malignancy. In circumstances requiring the evaluation of traumatic wounds involving extremities, imaging can be obtained of the vascular anatomy to assess vascular injury with angiography or CT angiography.
Pedicle perforator flaps
PPF have introduced a paradigm shift in the planning of reconstructive surgery, particularly introducing a significant element of freedom in flap design, resulting in multiple options for wound closure. Using the hot-spot principle, and familiarity with the location of dominant perforators, PPF can be harvested on any substantially sized perforator with the aid of a Doppler. Depending on the location of the pedicle in the designed flap and the length of pedicle dissected, flaps can achieve significant rotational freedom. The propeller flap can achieve complete 180° rotation with appropriate surgical planning and execution. PPF can be used for reconstruction of defects located on the trunk, head and neck, and extremities. Examples of commonly used perforators for PPF include perforators from the superficial femoral artery, deep inferior epigastric artery, profunda artery, descending branch of lateral circumflex femoral artery, and lateral superior genicular artery.
Freestyle perforator flap
However, it is important to understand that PPF are not limited to known dominant perforators, and there is no need to rely on conventional flap design. This liberty has resulted in the freestyle perforator concept of designing a flap on any dominant perforator adjacent to the defect for ad hoc reconstruction ( Fig. 10 ). The ability to raise a freestyle flap on a single dominant pedicle has been further revolutionized by Wei and Mardini, by raising freestyle free perforator flaps.
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