Perforator flaps are vascularized areas of skin and subcutaneous tissue receiving blood supply from one or more perforators originating from a named source vessel. The perforating vessels can pass directly from the source vessel without traversing any deep structures or indirectly through muscle. This has clinical relevance with regard to the ease and speed with which flaps can be raised. Flaps with an intramuscular perforator path are more challenging and time consuming to raise. Angiosomes and perforasomes are not identical. Taylor and Palmer1 described the 40 angiosomes in 1987, and Taylor2 subsequently related them to perforator flaps in 2003. Angiosomes represent a composite unit of skin and the underlying tissue supplied by a given source vessel. However, it was Saint-Cyr et al3 who described the perforasome theory, representing a similar concept, but the composite tissue is based on a single perforator from a given source vessel. This means that multiple perforasomes form each angiosome and in consequence there are around 300 perforasomes described (Fig. 5.1).
“Hot spots” are described as cutaneous areas of the body which are known to have high perforator density. Accordingly, areas of lower density are described as “cold spots.” The clinical relevance of this is that flap design incorporating a “hot spot” should ensure maximum inclusion of perforators and their required linking vessels, leading to more robust flap design and better chances of complete flap survival. The key hot spot areas are shown in Fig. 5.2. The term is not related to high-density areas of nerve endings which would lead to increased pain levels associated with surgery. Although there are temperature-based modalities available which can be used for postoperative flap monitoring, such as surface temperature assessment and differential thermometry, they do not have an association with the “hot spot” terminology.
No single classification system for perforator flaps is universally accepted, but the two most commonly used are the Canadian classification system and the Gent consensus. In the Gent consensus, the flap is either named after the nutrient source vessel (e.g., deep inferior epigastric perforator [DIEP] flap) or the associated muscle or anatomic region in cases in which the source vessel supplies many other flaps (e.g., anterolateral thigh perforator [ALTP] or tensor fascia lata perforator [TFLP] flap).1 The Canadian classification system also names the flap according to the source vessel, with the addition of the word artery (e.g., deep inferior epigastric artery perforator [DIEAP] flap). In this system, when the source vessel supplies more than one flap, additional abbreviations are added. For example, a lateral circumflex femoral artery perforator flap involving the tensor fascia lata is named LCFAP-tfl2 (Fig. 5.3).
The anterolateral thigh flap is a fasciocutaneous flap that may be based on the transverse branch of the lateral circumflex femoral artery, but the dominant supply is the descending branch. The correct Gent nomenclature1 for the anterolateral thigh flap is ALTP, whereas the Canadian classification system nomenclature 2 is LCFAP. This becomes LCFAP-vl when the vastus lateralis is perforated (myocutaneous) and LCFAP-s when it is purely septocutaneous. The flap can be described using the Mathes and Nahai system according to the course of the perforator. This classification contains three subtypes: A, B, and C. Type A is a direct cutaneous flap, type B is a septocutaneous flap, and type C is a musculocutaneous or myocutaneous flap.3 The ALT can be a septocutaneous flap (i.e., type B) and this is most easy to raise as no intramuscular dissection is required. Often there are perforators passing through the vastus lateralis and in this case it would be a type C flap. This dissection is more time consuming and risks damage to the perforating vessels.
well. Which one of the following is correct regarding the use of an anterolateral thigh (ALT) flap for this patient’s The ALT flap is a versatile flap that in many cases would be ideal for reconstructing the dorsum of the foot and ankle because it is often thin, pliable, and has a long pedicle enabling reach to the anterior or posterior tibial vessels. Furthermore, it can be raised as a chimeric flap with two separate skin paddles if there are separate defects involving medial and lateral malleoli, and it can limit surgery to a single limb.1 However, in obese individuals such as in this patient, the ALT flap is often too thick and bulky for dissection for reconstruction of the dorsal foot. For this reason, flap thinning would be required to convert the flap to a “super thin” perforator flap. Alternatively, a thinner flap such as a radial forearm could be used instead as obese patients’ radial forearm flap normally remains relatively thin.2,3 ALT skin paddle dimensions may be as large as 25 by 35 cm in some cases and flaps less than 10 cm width, such as in this case, can usually be closed directly. Those wider than 10 cm are likely to require a skin graft to the donor site. However, this figure is still variable depending on individual patient’s tissue characteristics. Preoperative angiography can be useful for evaluation of perforator flap vascularity but is not essential. It is more likely to be useful to confirm leg vascularity and availability of recipient vessels, particularly in cases following lower limb trauma or in patients with peripheral vascular disease.4 Fig. 5.3 An example of standardized muscle perforator nomenclature as per the Canadian system using the tensor fascia lata. (From Blondeel PN, Morris SF, Hallock GG, Neligan PC, eds. Perforator Flaps: Anatomy, Technique & Clinical Applications, 2nd ed. St Louis: Quality Medical Publishing, 2013.) Muscle name In this case, the tensor fascia lata Artery perforator Source vessel name In this case, the lateral circumflex femoral LCF AP -tfl
The deep inferior epigastric artery (DIEP) flap is a commonly used flap for both free tissue transfer in breast reconstruction, and locoregional transfer for reconstructing defects of the abdomen, genital region, and thighs. It has many advantages including a favorable donor site, a long vascular pedicle, low donor site morbidity, and the ability to convert to a traditional myocutaneous flap if the perforating vessels are poor. A disadvantage to this flap is that there is significant anatomic variation from patient to patient. Even within a single patient, there can be unpredictable side-to-side differences in perforator anatomy. This means it can be hard to anticipate the precise anatomical path and location of any given perforator. For this reason, preoperative imaging with computed tomography (CT) angiography is considered by many surgeons to be both useful and worthwhile in order to map the perforators and their relations to the skin and underlying muscle and fascia. Not only can perforator location present a challenge to the surgeon, perforators may also have a long intramuscular course and be closely located with the inscriptions of the rectus abdominis, thereby making their safe dissection more difficult. Intraoperative decision-making is probably the most challenging part of DIEP flap elevation as the wrong choice of perforator can result in partial or full flap loss.1–3
The flap as described is showing signs of venous compromise. This can occur in DIEP flaps where there is inadequate connection between the superficial and deep inferior epigastric vascular systems. In cases such as this, where the venae comitantes are small, it is likely that the superficial system is large. When raising a DIEP flap the SIEV should be identified and preserved at the inferior margin of the flap and where compromise occurs, it can be anastomosed to a suitable vein. This is the most appropriate step in this scenario. In general, venous compromise can be due to a number of factors which must be systematically addressed. First, the anastomotic patency must always be checked to ensure flow and that no external compression or twisting of the pedicle has occurred. In this case, the anastomoses are working satisfactorily. If one area of the flap (usually zone IV) is congested, this may be removed; but this has been done already. If the flap becomes brisk after inset, it may be that compression is the cause and release of inset and staged closure may be helpful. Systemic heparin is not likely to benefit in this situation given the venous compromise. Use of leeches can help small flaps such as those on the digits that have congested venous but would not be the first choice in this scenario.1–4
When raising perforator flaps, dissection around the perforator must be meticulous with limited vessel manipulation such as twisting, stretching, and grasping. Dissection should be close to the vessel within the loose areolar plane as this facilitates good visibility of the vessel and minimizes risk of inadvertent damage. The minimal perforator diameter is 0.5 mm rather than 2.0 mm and the presence of a visible or palpable pulse is a strong indicator of a good perforator. Having the perforator centrally within the skin paddle is not required and in some propeller freestyle flaps the perforator is deliberately offset (Fig. 5.4). The number of perforators that should be included in a flap is debated. DIEP flaps can be satisfactorily raised on single perforators, but some authors suggest that fat necrosis is reduced where more perforators are included.1,2 Perforator quality is probably more important than perforator quantity for any given flap.2 Fig. 5.4 A, Propeller flap concept. B, Propeller flap. (A and B Adapted from Zenn MR, Jones G, eds. Reconstructive Surgery: Anatomy, Technique, and Clinical Applications. St Louis: Quality Medical Publishing, 2012.) A B A + B Closest suitable perforator A B A + B (A) (B) Defect
Preoperative methods for assessing perforator flaps include handheld Doppler, CT angiography duplex ultrasonography, and magnetic resonance angiography (MRA). Of these, the handheld Doppler will be ideal for most applications like this case where a freestyle flap is to be used because it is simple and reliable to help locate individual perforating vessels. CT angiography is more useful in flaps with variable anatomy such as the DIEP or superior gluteal artery perforator (SGAP) flap but is not essential when handheld methods can suffice. Indocyanine green is a useful intraoperative technique to help identify zones of adequate perfusion before committing to flap design. Laser Doppler flowmetry and tissue oximetry are methods used to monitor flaps postoperatively. They have high positive and negative predictive values but are expensive and not routinely used. Thermal smartphone imaging is a newly described and potentially useful tool for preoperative flap planning. It may also find a role in intraoperative assessment and postoperative monitoring. It utilizes infrared radiation that can detect dense areas of perforating vessels and tissue perfusion via temperature variations. It does not involve intravenous (IV) contrast or ionizing radiation exposure. In one study by Pereira et al in 2018,1 this modality was compared with CT angiography in 20 patients undergoing ALT harvest for limb reconstruction. Within these patients, a total of 120 ALT flap perforators in 38 territories were identified. This study showed very high specificity and sensitivity (98 and 100% respectively) in detecting perforators identified by CT angiography.
As discussed in question 3, the LCFAP flap (also known as the ALT flap) is based on the lateral circumflex femoral artery and perforating vessels from this source vessel may pass through a portion of the vastus lateralis en route to the skin. In some cases, the perforators may be completely septal, and in this situation intramuscular dissection is not required. Dissection of the gracilis muscle is required when raising an MCFAP flap which arises from the medial circumflex femoral vessels or the transverse upper gracilis (TUG) flap.1,2 Intramuscular dissection of the medial head of gastrocnemius is required when raising a medial sural artery perforator (MSAP) flap.3 Perforator flaps have also been described based on the short head of biceps femoris and these may arise from either the popliteal or profunda femoris vessels.4 In spite of a number of new perforator flaps having been described, the LCFAP and ALT remain the most popular workhorse flaps in reconstructive surgery.