Chapter 4: Basics Of Flaps

Neurocutaneous flaps (such as the sural flap) receive their blood supply through the arteries accompanying the nerve.1 Fasciocutaneous flaps are supplied by different levels of vascular plexus including the subfascial, intrafascial, and the intradermal layers, but the suprafascial and subdermal plexuses are considered to be the most important. Axial pattern flaps contain a specific direct cutaneous artery within the longitudinal axis of the flap. Examples include the pedicled groin and paramedian forehead flaps. This means they are not limited by specifically set width to length ratios. An angiosome refers to a composite unit of skin and the underlying deep tissue supplied by a source artery, not just the skin area alone. The sympathetic (not parasympathetic) system is most important in regulating blood flow to the skin. Flaps based on the subdermal plexus that are limited to particular width to length ratios are described as random pattern flaps; for example, a transverse rectangular advancement flap on the forehead.2–4

A flap is a unit of tissue that has its own blood supply and may be transferred from one part of the body to another using this blood supply. There are a number of different ways to classify flaps including the vascularity, the method of movement, and the tissue composition. Having a thorough understanding of the classification categories and their subtypes is useful in understanding the principles of flaps. Furthermore, although there are merits in each of the different classifications used, the most clinically valid is the intrinsic vascularity, as it is the most critical determinant of a successful transfer.1,2

3. Taylor GI, Caddy CM, Watterson PA, Crock JG. The venous territories (venosomes) of the human body: experimental study and clinical implications. Plast Reconstr Surg 1990;86(2):185–213

4. McGregor IA, Morgan G. Axial and random pattern flaps. Br J Plast Surg 1973;26(3):202–213

The Mathes and Nahai classification1 of muscle flap supply is as follows: Type I: One vascular pedicle (e.g., tensor fascia lata) Type II: One dominant and one or more minor pedicles (e.g., gracilis) Type III: Two dominant pedicles (e.g., gluteus maximus) Type IV: Segmental vascular pedicle (e.g., sartorius) Type V: One dominant pedicle with secondary segmental pedicles (e.g., latissimus dorsi) Types I, III, and V have the most reliable blood supply for transfer as the entire muscle can be moved based on a single pedicle or segmental branches. The TFL flap is a type I flap as it has one dominant pedicle arising from the lateral circumflex femoral artery. It may be harvested with an anterolateral thigh (ALT) flap: The gluteus maximus is a type III flap (not type II) as it has two dominant vascular pedicles, namely, the superior and inferior gluteals. This means that the entire muscle can be based on either vessel. An example of a type IV flap is the sartorius. The challenge of using such a flap for reconstruction is that the segmental blood supply limits movement as a pedicled flap to ensure vascularity is maintained. It would not be useful as a free flap because only part of the muscle can be harvested on any given segmental supply. One scenario where the sartorius is used clinically is in a switch procedure during groin dissection for large vessel coverage. In this setting, the upper segmental supply is sacrificed to allow movement of the muscle. The latissimus dorsi muscle is a real workhorse muscle flap in plastic surgery and is classified as type V by the Mathes and Nahai classification. It can be moved as a pedicled flap on either the segmental supply or main pedicle to reconstruct the chest wall and back areas, or as a free flap based on the main pedicle (thoracodorsal artery) (Fig. 4.2).

The use of myocutaneous flaps has been associated with a decrease in bacterial contamination within wounds compared with the use of fasciocutaneous flaps to reconstruct the same defect.1,2 They are therefore generally accepted to be preferable in wounds associated with recent infection such as an osteomyelitis case or a delayed open fracture soft tissue cover. Muscle flaps are also well suited for coverage of irradiated and more general traumatic wounds. Other advantages include the ability to obliterate dead space, and relative ease for flap raising. The pliability of a muscle flap is generally less than the equivalent fasciocutaneous flap due to flap bulk, and muscle flaps require split skin grafting unless a skin paddle is included. Taking muscle is likely to slow the postoperative rehabilitation rather than accelerate it, and would also tend to increase the donor site morbidity.3,4

There are a number of advantages of vascularized bone flaps over nonvascularized alternatives. One of the main advantages is the ability to insert osseointegrated implants into the vascularized flap at the time of transfer. This is particularly useful in mandibular and maxillary reconstruction to provide dentition. The other key advantages are that larger bone defects can be reconstructed, they tend to undergo primary bone healing, and they withstand irradiation well (particularly important if adjuvant radiotherapy is indicated following tumor resection and reconstruction). Furthermore, most bone flaps can be harvested with skin or muscle to provide lining for the defect. The downsides are that a different set of surgical skills are required and surgical time is increased. Donor site morbidity may also be increased, although the disability associated with bone flap harvest is relatively low (see Box 4.3).1–3 BOX 4.3 ADVANTAGES AND DISADVANTAGES OF VASCULARIZED BONE FLAPS Advantages Can reconstruct large bony defects Undergo primary bony healing Withstand radiation and implantation Can be transferred as a composite with other tissue types (e.g., scapular flap and free toe transfers) Disadvantage Donor site morbidity

Prefabrication is a form of flap manipulation where a new dominant vascular pedicle is buried in the planned flap territory prior to transfer. Approximately 6 weeks later, the flap is then elevated based on the new pedicle and transferred. Prefabrication is not a commonly used technique, in contrast to prelamination, which also involves two stages. The principle of prelamination is to reconstruct the new body part with composite tissues prior to transfer. In this way bone, cartilage, or skin grafts may be added to the flap in its original position based on the native blood supply. Examples of this in clinical practice include nasal reconstruction with either the forehead or radial forearm flaps. In fact, this is an approach typically reserved for head and neck reconstruction.1–3

Local flaps can be subclassified as rotation, advancement, transposition, or interpolation. Rotation flaps often have a semicircular design and rotate about a pivot point into an adjacent defect (Fig. 4.3). Direct closure of the donor site is usually possible. Use of a back-cut or Burow’s triangle at the base will change the pivot point which can increase the reach of the flap tip. Advancement flaps slide into an adjacent defect by stretching the skin or releasing subcutaneous tissues without rotation or lateral movement. They can be rectangular or V-Y shaped, and may be of single or double pedicle design. Incorporating small Burow’s triangles at the base can increase advancement distance (Figs. 4.4 and 4.5). Transposition flaps have elements of rotation and lateral advancement, and they rotate around a pivot point into an adjacent defect. Common examples include rhomboid flaps and Z-plasty flaps (Fig 4.6). Fig. 4.3 Rotation flap. (*, Pivot point.) Line of maximal tension Backcut Burow’s triangle Fig. 4.4 Rectangular advancement flap. Burow’s triangles allow increased advancement and eliminate dog-ears. Fig. 4.5 V-Y advancement flap. The triangle of skin should have a length two to three times the diameter of the primary defect and a width equal to the greatest width of the primary defect. Although Limberg and Dufourmentel flaps are both transposition flaps of a rhomboid design, they differ in the individual internal angles used. The Limberg flap is a rhomboid flap that uses two 60-degree angles and two 120-degree angles. The Dufourmentel flap is a narrower design with internal angles that are not fixed to specific numbers. The benefit of this flap is that it has a lesser arc of pivot and therefore reduces the likelihood of a dog-ear being created.1

A Z-plasty is a type of transposition flap with two adjacent triangular flaps that are reversed. Key factors in the design are that the three limbs should be of equal length, and the two internal angles should be equivalent (see Table 4.1, Essentials of Plastic Surgery, third edition). There is a consistent theoretical relationship between internal angle and percentage gain in central limb length. An angle of 30 degrees will allow an increase of 25%. Thereafter, for each increase in angle of 15 degrees, length increases by 25% (e.g., a 45-degree increase in angle gives a 50% increase in length, and a 60-degree increase in angle gives a 75% increase in length). In clinical practice actual gains in length may differ from the theoretical values because of skin laxity and adherence (Fig. 4.7).1–5 Fig. 4.6 A, The effective length of a flap becomes shorter the farther the flap is rotated. Therefore, it should be designed longer than the defect. B–E, Transposition flap. (*, Pivot point; LMT, line of maximal tension.) A B C D E 0° 180° LMT a b True arc Fig. 4.7 Z-plasty. Projected position of transverse limb Central member Limb Limb Contractural diagonal lengthens when scar tissue cut 60° 60° y x x y

The double-opposing Z-plasty technique involves a curvilinear modification of the Z-plasty principle and is used to close circular defects (Fig. 4.8). A 60-degree, rather than a 75-degree Z-plasty, provides the best compromise for achieving increased central limb length without significant lateral tension (see Fig. 4.7). Although combining multiple Z-plasties in series is a useful technique, more effective skin lengthening is achieved with a single, large Z-plasty. A number of techniques involve Z-plasties, such as the jumping-man flap and four-flap Z-plasty. Both of these can be useful for correction of first web space tightness (see Fig. 72.7, Essentials of Plastic Surgery, third edition). The jumping-man flap or double-opposing Z is created with a combination of Z-plasty flaps and a central V-Y advancement flap. The four-flap Z-plasty moves flaps from an initial ABCD orientation to CADB orientation following transfer. The actual gain in the central limb length following a standard Z-plasty differs from the theoretically predicted value. This can range from 55 to 84%. Use of the 90-degree Z-plasty provides a large theoretical gain in length but results in high tension across the wound closure.1,2 Fig. 4.8 Double-opposing semicircular flaps. (Adapted from Keser A, Sensoz O, Mengi AS. Double opposing semicircular flap: a modification of opposing Z-plasty for closing circular defects. Plast Reconstr Surg 102:1001, 1998.) A A A B B X’ X’ X X’ A’ A’ A’ B’ B’ X X

Blood flow to the skin is regulated by local and systemic factors. Systemic factors are neural through sympathetic adrenergic fibers and humeral through a number of chemical mediators. Thromboxane A2 is a humoral vasoconstrictor, as are epinephrine, norepinephrine, serotonin, and prostaglandin F2a. Circulating vasodilators include bradykinin, histamine, and prostaglandin-E1. Local control is affected by metabolic factors including hypercapnia, hypoxia, and acidosis. Each of these acts primarily as a vasodilator.1,2

requirement. Flap delay involves surgical interruption of a portion of the blood supply to a flap prior to transfer. It may be useful to improve the viable length of a given flap (i.e., improve tip viability) but it does not significantly affect more proximal areas such as the base which would have survived anyway. It requires two surgical procedures typically spaced 10–21 days apart. Although in animal models, flaps have been successfully divided at 3 days, this time interval is not normally advised in clinical cases. Flap delay should not result in tissue necrosis as vascularity should not be compromised to such an extent. The process should cause a milder degree of tissue ischemia. There are two main theories regarding delay: that delay conditions tissues to ischemia allowing them to survive on less nutrient blood flow and that delay improves vascularity by opening up choke vessels between adjacent vascular territories. It is likely that a combination of these effects is responsible. The five mechanisms believed to be involved in delay are sympathectomy, vascular reorganization, reactive hyperemia, acclimatization to hypoxia, and a nonspecific inflammatory reaction. Therefore, loss of sympathetic stimulation, as opposed to an increase in sympathetic stimulation, is proposed to be a factor in delay.1,2

Of the medications listed, low-molecular-weight heparin has been shown to improve anastomotic patency while minimizing hemorrhage.1 Dextran was originally used as a volume expander and can decrease platelet adhesiveness and procoagulant activity. It also increases bleeding time and has been shown to improve short- term microvascular patency. However, it is not routinely used because of its poor side effect profile including anaphylaxis, pulmonary edema, renal failure, and cardiac complications.2–6 Calcium channel blockers act on vascular smooth muscle and have been shown to improve flap survival in animal models, with no significant publications in human free flaps.7 Aspirin acts on the cyclooxygenase pathway and decreases the synthesis of thromboxane A2, a potent vasoconstrictor. Although some evidence suggests that anastomotic patency may be improved in the first 24 hours, beyond this time no further improvement is observed. There is currently no evidence to support the routine use of aspirin following free flap surgery.8

There are a number of potential reasons for flaps to fail including local factors such as a lack of arterial supply into the tissues, infection, bleeding, swelling, technical error, and trauma, as well as systemic factors such as poor nutrition, poor oxygenation, and poor compliance with postoperative care. However, the most common primary cause of flap failure across all flap types is venous insufficiency and this itself may occur secondary to some of the causes mentioned above. Venous insufficiency initially presents with signs of congestion including purple/blue discoloration and brisk capillary refill. Later, deepening of the purple color and fixed staining are key features. In free flaps, the venous insufficiency may be due to venous thrombus, or twisting or compression on the main vascular pedicle near to the anastomosis. Alternatively, there may be intrinsic venous failure within a flap as is seen in failing random pattern flaps and in the later stages of free or regional flaps where intravascular flap thrombi are features. It is important to recognize venous insufficiency early post surgery, as there may be steps taken to reduce or reverse this and avoid flap failure.1–6

Different tissues are able to tolerate periods of ischemia differently. This is clinically relevant in free flap transfer because the flap “off time” or ischemia time needs to be carefully limited. This is particularly true of flaps containing muscle or bowel, which tolerate prolonged ischemia poorly. It is generally accepted that the safe ischemia times for skin and bone are longer than those for other tissues (up to 3 hours). Tubed-pedicled reconstruction is an older method of reconstruction that has been largely superseded by free flap surgery. However, there may be situations where such an “old school” approach is warranted. One example is the tubed paramedian forehead flap for nasal reconstruction which is still in use. This type of procedure takes at least two stages in all cases, but to move a distance such as the groin to the neck would take additional stages. Functional muscle transfer is a useful way of replacing lost active joint function after nerve or muscle damage. The process can be performed with locoregional, pedicled transfer such as the latissimus dorsi for elbow flexion. Free flap functional muscle transfer includes the gracilis for facial reanimation. Any muscle transfer will require a blood and nerve supply, but coaptation is usually only required in free transfer as the usual nerve supply otherwise remains intact, e.g., latissimus dorsi transfer (thoracodorsal nerve). In free tissue transfer such as the gracilis to face, the nerve to gracilis (obturator nerve) may be coapted onto the hypoglossal nerve, nerve to masseter, or a cross face facial nerve graft. In terms of muscle tension for functional transfer, this should be set at the same tension as the transferring muscle was set for its original function, not tighter. Ischemia-induced reperfusion injury (IIRI) describes a process whereby direct cytotoxic injury occurs from accumulation of oxygen derived free radicals during flap ischemia. It is therefore a phenomenon of free tissue transfer rather than one of pedicled flaps.1

Medicinal leeches (Hirudo medicinalis) are used in patients where there is significant venous compromise in a flap and there are no surgical alternatives to improve venous outflow. They secrete a number of substances that affect coagulation. First, they inject hirudin (a naturally occurring anticoagulant that inhibits conversion of fibrin to fibrinogen) at the site of a bite. Second, they secrete hyalase which facilitates spread of hirudin through tissues, and third, they secrete a vasodilatory substance that also contributes to bleeding. They also have a mechanical effect of creating physical channels through which venous drainage can occur. Use of medicinal leeches carries a risk of infection from the gram-negative rod (Aeromonas hydrophila) (not mycobacterium) and for this reason, antibiotics should be prescribed prophylactically. The antibiotic of choice would not be amoxicillin/clavulanate as there is resistance to this antibiotic by Aeromonas hydrophila. Instead, all patients having leech therapy should be prescribed fluroquinolones such as Ciprofloxacin. The other risks of leech therapy include anaphylaxis, irrespective of nut allergy status, persistent bleeding, and excessive scarring. Furthermore, many patients will find them difficult to tolerate. That said, they can be beneficial in some cases.1–3

18. You are asked to assess a patient 24 hours after breast reconstruction with a DIEP flap. Which one of the following Cutaneous free flap monitoring is predominantly based on clinical assessment, although a number of adjuncts are available. Common clinical features assessed are tissue color, capillary return, tissue turgor, flap temperature, and dermal bleeding characteristics. Of these features, all can usually be used to discriminate between venous and arterial insufficiency with the exception of temperature, which is usually reduced in either case. A healthy flap should have a capillary refill time of 2–3 seconds. It should be a healthy pink color in pale skinned individuals. Tissue turgor should be normal. Low turgor indicates underfilling of the flap (i.e., arterial compromise) and increased turgor indicates venous congestion. Needle testing of the dermis can be helpful as a healthy flap should bleed bright red blood. No blood or serous fluid indicates there is no inflow and dark red blood suggests there is inadequate venous outflow (Table 4.1).1 Table 4.1 Signs of Arterial Occlusion and Venous Congestion Arterial Occlusion Venous Congestion Skin color Pale, mottled, bluish, or white Cyanotic, bluish, or dusky Capillary refill Sluggish Brisker than normal Tissue turgor Prune like; turgor decreased Tense, swollen; turgor increased Dermal bleeding Scant amount of dark blood or serum Rapid bleeding of dark blood Temperature Cool Cool

Despite a number of technologically advanced tools for monitoring free flaps, clinical observation remains the most widely used and consistent method for monitoring a free flap. Of the clinical assessment modalities, bleeding from a dermal wound is an accurate positive test, as the absence of bleeding indicates no arterial inflow, and dark red blood indicates venous outflow insufficiency. A failed flap will leak serous straw-colored fluid on dermal scratch testing. It is paramount to educate nursing and medical staff in accurate flap monitoring so that changes in flap appearance are identified and managed early. In buried flaps such as a bony fibula flap for reconstruction of the humerus, direct clinical observation of the flap is not possible so an internal Doppler placed on the artery or vein can be helpful. This involves securing a cuff around the vessel with ligaclips. The cuff is placed distal to the anastomosis and has a wire attached that connects to an external box providing audible confirmation of blood flow.1

Free flaps most commonly fail in the early postoperative period due to failure of the main flap anastomoses. When taken back to the operating room, a common finding is thrombus. A number of studies have shown successful flap salvage using intra-arterial injection of tissue plasminogen activator (TPA). Thrombolytic agents such as this stimulate the conversion of plasminogen to plasmin, which acts to cleave fibrin and breaks down thrombus. The first-generation agents included streptokinase and urokinase. Second-generation agents include tissue plasminogen activator (t-PA) and acylated plasminogen-streptokinase activator complex (APSAC). To use a product like t-PA successfully, it must be delivered directly into the flap vessels, so it is necessary to create an arteriotomy or open a small branch proximally in order to flush it through.1–4, Drugs that reduce vasospasm (i.e., vasodilators) are important in free flap surgery as dissection of vessels and general handling of them in preparation for the transfer tend to cause vasoconstriction. However, none of these are especially helpful in free flap salvage as in this case. Examples include lidocaine, calcium channel blockers such as verapamil, pentobarbitol, and papavarine. Nitroglycerin is also a topical vasodilator but its use in plastic surgery has been associated with improved survival of local skin flaps in animal models.5 More recently, a large review compared the use of intraoperative use of nitroglycerin to prevent vasospasm as an alternative to papavarine and the results suggest this is an effective alternative for this purpose.6

21. You are writing the postoperative instructions for monitoring of a free anterolateral thigh (ALT) flap following Postoperative free flap monitoring is very important in terms of the ability to salvage a flap if it changes in the early postoperative period and that change is identified early. Free flaps are most likely to stop flowing within the first 24 hours and then the risk of problems progressively decreases over the following days. Given this, it is important to have very regular observations in the first 24-hour period following surgery. Therefore, most surgeons will request hourly observations of the flap itself and other key patient parameters such as blood pressure, pulse, fluid balance, oxygen saturations, and respiratory rate. Flap observations for skin flaps will normally include tissue turgor and capillary refill and may include either internal or external Doppler assessment and temperature assessment. Hourly observations in this time frame provide a balance between overly arduous assessments, e.g., every 30 minutes, and yet a sufficiently early opportunity for the nursing and medical teams to act swiftly if a return to the operating room is required. Observations 2, 3, or 4 hourly in the first 24 hours would not provide this. Recognition of a failing flap can enable the clinician to arrange a return to the operating room on an urgent basis. The cause of the failing flap can be identified and hopefully corrected. In a number of studies, it has been shown that salvage of failing free tissue transfers is most effective in the first 24 hours.1 In the second and third 24-hour periods, the risk of flap failure is less and therefore it is generally considered acceptable to reduce the intensity of the observations in this time period. There will be variations in the precise timing and factors specific to each case need to be considered. However, a sensible approach would be to drop down the observations to 4 hourly at this stage post surgery. This again provides a balance of reasonable monitoring. In general, the ability for successful flap salvage decreases as the time interval since surgery increases, while at the same time, the likelihood of the flap failing spontaneously also decreases. For this reason, the intensity within the first and second time periods will normally be different.