Overview of flaps for soft tissue reconstruction

INTRODUCTION — A tissue flap is defined by a persistent blood supply and does not depend on the recipient bed to perfuse the donor tissue (unlike unvascularized skin grafts). With modern techniques, an almost endless array of flaps is available to choose from to provide coverage for even the most complex defects.

Flaps are very versatile and can be used to fill large defects, recreate structures such as the breast, or provide better coverage over joints. Flaps, such as the gracilis flap, are available to be transferred as complete muscle units, allowing return of function when connected to recipient nerves. The transferred tissue volume can contain multiple types of tissue, including skin, muscle, nerve, fascia, and bone. The higher volume of tissue transferred demands constant perfusion and will be compromised if the arterial supply or venous drainage is interrupted during or following the transfer of the tissue. Donor site morbidity is often minimal but can be significant depending on the flap chosen.

The routine use of flaps has dramatically broadened the ability of the surgeon to care for the injured patient. In addition, previously unresectable cancers have become resectable with the ability to offer flap reconstruction. The ability to move tissues around has improved the quality of life for countless patients. Quality of life and cosmetic outcomes are steadily improving as flaps with lower morbidity are developed, with technical success rates approaching nearly 100 percent.

This topic review will discuss the general approach to the use of flaps in reconstructive surgery, including the nomenclature of flaps and preoperative and postoperative considerations, including complications. The use of skin grafts for reconstruction is reviewed separately. (See "Skin autografting".)

FLAP NOMENCLATURE — A flap is a transfer of tissue with its intrinsic blood supply from one part of the body to another. The blood supply to a flap is persistent and does not depend on the recipient bed. Multiple classifications have been described, but, in general, flaps for reconstruction are classified based upon the type of blood supply (ie, random, axial), proximity of the donor tissue to the recipient (ie, local, regional, distant), and tissue composition (eg, musculocutaneous, fasciocutaneous) [1]. Flaps can also be further classified based upon how the donor tissue is transferred into the recipient tissue defect (eg, rotation, advancement).

Free skin grafts (split thickness, full thickness) are examples of the transfer of nonvascularized tissue that relies upon a well-vascularized recipient bed to "take." The use and creation of skin grafts is reviewed separately. (See "Skin autografting".)

Blood supply — The blood supply to a flap can be random or derived from a named source (ie, axial).

Random flap — Random skin flaps contain only skin and/or subcutaneous tissue and as such, the blood supply to a random flap is provided by the many small unnamed vessels of the subdermal plexus. These flaps are in close proximity to the recipient site. (See 'Local' below and 'Skin' below.)

Axial flap — Axial flaps take advantage of regional areas perfused by named blood vessels (ie, the angiosome). The description of the areas of flow for each vessel were originally determined by cadaver dissection. Most flaps will survive if the tissue transferred contains the vessels responsible for perfusion to that area and, at most, one additional neighboring vascular territory. The angiosome concept has revolutionized flap design, adding anatomic understanding to prior clinical experience [2-4]. Axial flaps may consist of skin, subcutaneous tissue, muscle, and/or bone; can be pedicled; and can be used regionally or transferred a distance as a free flap. (See 'Regional' below and 'Distant' below and 'Composition' below.)

Pedicled — With a pedicled flap, the vascular supply remains connected anatomically throughout flap transfer. Examples of distant pedicled flaps include the omental flap transferred to the chest and the transverse rectus abdominis muscle (TRAM) flap (figure 1). (See 'TRAM flap' below.)

Free tissue transfer — For free flaps, the artery and at least one vein are disconnected during the transfer and reconnected microsurgically to a new artery and vein at or near the recipient site. The creation of a free flap is complex and requires a substantial level of training, planning, and surgical expertise.

Free flaps are most often used in the following situations:

●When less complex reconstructive methods have failed

●When deep structures are exposed (eg, calvarium, frontal sinus, nasal pyramid, tibial crest, neurovascular structures, tendons)

●When there is an absolute need to combine reconstruction with cosmetic appearance, such as with the facial structures or the female breast

●When donor site morbidity will be reduced by using microsurgical transfer (eg, deep inferior epigastric flap [DIEP] versus with transverse rectus musculocutaneous flap [TRAM] for breast reconstruction)

●With increasing experience, often a free flap is found to offer the least donor morbidity and the best functional and/or aesthetic outcome

Perforator flaps are a special type of free tissue flap that contain a transmuscular and/or transfascial vascular "leash" or pedicle that leads to the overlying fascia and/or skin only [5]. The vessels are dissected out of the muscle through which they perforate, and the muscle is left behind, relatively undamaged. Perforator flaps are technically demanding and more time consuming to create than pedicled flaps [6,7]. These flaps have gained favor as a way to decrease the morbidity associated with musculocutaneous flaps. Free tissue transfer has become commonplace in breast reconstruction using the deep inferior epigastric perforator flap, which is an alternative to the pedicled TRAM flap (figure 2) [8,9]. (See 'DIEP flap' below.)

Proximity of flap donor and recipient sites

Local — Local flaps use tissue that abuts the defect that requires coverage. A limitation to the use of local flaps is the availability of healthy, pliable, and well-vascularized donor tissue nearby. The donor site for a local flap ideally should have enough laxity to allow primary closure of the defect, in addition to providing tissue to the recipient site for coverage of the defect. Most local flaps can be performed under local anesthesia with or without sedation. Local flaps have the advantage of "like to like." The skin color, texture, thickness will all closely approximate the recipient site the closer the flap site is to the defect.

Regional — Regional flaps are pedicled flaps that use tissue in the vicinity of the defect without actually abutting the defect. These flaps are transferred using a releasing incision along the course of the flap transfer or alternatively are transferred under a skin or tissue tunnel along the course. Any twist of the base of the pedicle or compression of the overlying bridge of tissue can lead to vascular compromise and tissue ischemia more distally in the flap. (See 'Blood supply' above.)

Regional flaps derive their vascular supply from the same anatomic area of the defect to be reconstructed. Regional flaps use skin similar in quality and color to the recipient site, so they are favored in the face, head, and neck when compared with distant flaps or even skin grafts. In the face, using "like tissue" is very important for the long-term aesthetic result. Regional flaps are sometimes used in the trunk or extremities.

An example of a regional flap is the forehead flap for nasal tip reconstruction, which is based on the supraorbital and supratrochlear vessels and includes the glabellar and frontalis musculature. Another is the radial forearm flap, based on the radial artery, which can be used to cover a defect in the hand. (See 'Forehead flap' below and 'Radial forearm flap' below.)

Many regional flaps are musculocutaneous in nature. Therefore, one must take into account the morbidity of muscle harvest and loss of the donor muscle function.

Distant — Distant flaps use tissue far from the defect and can be transferred over a large distance as pedicled flaps or free flaps. (See 'Blood supply' above.)

Numerous distant flaps have been described, including cutaneous, fasciocutaneous, osteocutaneous, musculocutaneous, and even pure muscle flaps. The newer designer flaps, prefabricated and prelaminated flaps, are also included in this category. All of these flaps are transferred with the same principles in mind. First and foremost is that adequate tissue to accomplish the goal is harvested from the recipient site. The donor tissue must be adequately vascularized throughout, and donor site morbidity should be kept to a minimum.

The omental flap to the chest is an example of a distant pedicle flap while a free transverse rectus abdominis flap is an example of a microsurgical free distant flap. (See 'Omental flap' below and 'TRAM flap' below.)

Composition — Local, regional, and distant flaps can contain a variety of tissues [10].

Skin — Skin-only flaps are most commonly used as local flaps, though microsurgical transfer of skin-only flaps (eg, scapular and parascapular flaps) has certainly been used.

●Random pattern type – Most commonly, skin flaps are random pattern flaps with no specific named vascular supply (see 'Blood supply' above). Local skin flaps are often used to cover defects from surgical lesion excision (eg, cutaneous carcinoma) or traumatic wounds in areas without enough tissue laxity to afford primary closure. One example is the use of local skin flaps to cover a defect on the face after Mohs surgery. If a local flap can be advanced to cover a defect, this is a simpler and aesthetically better method of providing closure than a skin graft, which would require surgery at a second site.

Local skin flaps must adhere to some simple rules with regard to size and shape. In general, the length of the flap cannot be longer than the base width of the flap (ie, 1:1 ratio) in most cases to ensure adequate vascular supply to the flap. This ratio is somewhat variable depending on the underlying vascularity. Flaps in highly vascular areas (eg, face) can be longer with a narrower base, while a poorly vascularized area (eg, lower extremity) requires that flap length be equal to flap width. Examples of random local flaps include rhomboid flaps (figure 3 and figure 4 and figure 5), V-Y flaps (figure 6 and figure 7), bilobed flaps, and flaps based on the Z-plasty principle (figure 8). (See "Z-plasty".)

●Axial type – The suprafascial flap contains skin and a fat-containing envelope and is based on vessels that perforate through muscles or through intermuscular septae. With these flaps, the muscle fascia is left behind. Suprafascial skin flaps can be transferred as regional or distant flaps and appear to be associated with less donor site morbidity and, particularly, less sensory disturbance [11]. Another type of axial skin flap is the fasciocutaneous flap, which is discussed below. (See 'Fasciocutaneous' below.)

Muscle — The blood supply of a muscle flap is carried through the muscle and may include the overlying tissue [12]. Muscle flaps are well vascularized, and, if skin coverage is inadequate, a split-thickness skin graft can be placed to complete wound closure. Muscle-only flaps are usually used for coverage of large ablative or trauma-induced defects, or for functional purposes.

●An example of a muscle flap for defect coverage is the medial gastrocnemius flap, which is based on the medial sural artery and vein. The medial gastrocnemius flap can be used to cover defects from the distal thigh down to the middle third of the calf and is often used in salvage of total knee replacement or to cover compound fractures of the proximal calf. (See 'Medial gastrocnemius flap' below and "Flap reconstruction of the lower extremity", section on 'Soft tissue flap reconstruction'.)

●Examples of muscle flaps as active transfers for functional purposes include a pedicled latissimus flap for elbow flexion and a free gracilis flap for facial reanimation.

Musculocutaneous — A flap composed of muscle and its overlying skin and subcutaneous tissue is a musculocutaneous flap [12]. The most common regional flaps are musculocutaneous flaps. Musculocutaneous flaps are used for large or deep defects, such as deep perineal defects, or to recreate structures, such as with breast reconstruction (eg, latissimus flap, TRAM flap) (figure 1) [13].

Fasciocutaneous — A fasciocutaneous flap is composed of skin, subcutaneous tissue, and the underlying fascia.

Fasciocutaneous flaps are commonly based on vessels arising in fascial planes in between muscles and do not intrinsically include any muscle in the design. These flaps are less bulky than musculocutaneous flaps and are used to cover large superficial defects when skin alone would not provide adequate coverage. An example of a fasciocutaneous flap is the buttock V-Y flap used for perineal reconstruction [14]. Another commonly used fasciocutaneous flap is an anterolateral thigh flap used to cover a perineogenital skin defect [15]. (See 'Anterolateral thigh flap' below.)

A perforator flap is another type of fasciocutaneous flap that consists of skin and subcutaneous tissue that is vascularized by a perforator artery (eg, musculocutaneous or septocutaneous) [5]. The vessels are dissected out of the tissue through which they perforate, and if the perforator is musculocutaneous, the muscle is left behind [16-18]. In this way, a large cutaneous flap can be obtained from the same region of a conventional musculocutaneous flap without the need to include the muscle, which might not be expendable. Perforator flaps have gained favor as a way to decrease the morbidity at the donor site [6,7]. As an example, the use of free tissue transfer has become commonplace in breast reconstruction with the use of perforator flaps, such as the DIEP flap (figure 2) [8,9]. (See 'DIEP flap' below.)

Osteocutaneous — An osteocutaneous flap is a flap containing a bony component. It is used to replace missing bone in the head and neck, or long bones of the extremities. An example of an osteocutaneous flap is a fibular free flap [19].

Designer flaps — Prelaminated and prefabricated "designer" flaps are limited to unusual circumstances when more common anatomic flaps are inadequate.

●Prelaminated – Prelaminated flaps are mostly used to replace a multiple-layer structure such as the nose. As an example, a radial forearm fasciocutaneous flap can be partially raised, and then cartilage and skin can be placed on the deep surface. When these become vascularized three to six weeks later, the entire construct can be transferred as a free microvascular transfer. Not all prelaminated flaps are prefabricated (eg, radial forearm flap with added cartilage and skin graft to create a trilaminar flap). However, prefabricated flaps can also be prelaminated.

●Prefabricated – Prefabricated flaps are created by using tissue without an axial vessel and adding a vascular leash at a first stage [20]. If a particular type or color of skin is desired for a reconstruction, an arterial-venous pedicle is transferred intact under that skin. Vascular connections will occur over a few weeks, and then the flap can be transferred as a free flap based on the transferred vascular pedicle. Neovascularization from the transferred pedicle occurs, allowing the transfer of tissue not normally in the vascular territory of the pedicle that is used. Prefabricated flaps have been used for reconstruction of large facial defects [21]. Using the delay phenomenon, tissue transfers can be engineered, enabling the surgeon to transfer tissue with layers not normally seen in the donor site. Radial forearm flaps with cartilage from the ear and a deep side skin graft have been prepared for use in nasal reconstruction [22].

PRINCIPLES OF RECONSTRUCTION — A flap is the best approach to wound repair when primary repair is not possible without undue tension or the wound bed is not amenable to grafting because the defect is not well vascularized, such as in those with exposed bone or tendon. Flaps are also the best approach for coverage of large defects or when complex tissue is required to regain normal aesthetics (eg, breast reconstruction) or function (eg, extremity reconstruction).

Recipient site evaluation and preparation — Flap selection begins with an analysis of the defect, including the location and condition of the recipient bed, comorbidities (eg, cigarette smoking, history of radiation therapy, diabetes mellitus), cosmetic significance, and functional significance. In addition to evaluating the defect to be closed, the surgeon must consider the donor site morbidity, including scarring and functional loss if the flap includes a muscle.

Included in this analysis are the location, size, and functional requirements of the area and exposure of any crucial structures. If the area has been subjected to radiation therapy, the wound is more susceptible to dehiscence and infection.

Prior to reconstruction of any wound bed, the surgeon must be sure that the recipient bed is properly prepared. The wound must be free of all necrotic or ischemic tissue. In addition, signs of infection such as local cellulitis, significant edema, or purulent drainage should have abated. However, in contrast to the use of skin grafts, the wound bed need not be well vascularized, since the flap has its own blood supply. Granulation tissue, if present, should be gently debrided back to the wound base to reduce levels of bacterial contamination. Skin margins should be trimmed back to expose healthy, unscarred dermis.

Irrigation of the wound bed prior to flap placement should be done to reduce bacterial contamination as much as possible. This is frequently accomplished with 3 to 6 liters of saline solution. Finally, hemostasis after debridement must be meticulous to prevent fluid collections from accumulating beneath the flap tissue.

Flap selection and donor site evaluation — Flaps have broad applicability and choice, with an almost endless array of flaps available to cover even the most complex defects. Aesthetic and functional results need to be taken into account, as well as comorbidities and potential donor site morbidity.

As a general rule, simple local flaps are used if possible. Regional flaps or distant flaps are used if local options are not available, or if a distant flap will give a better overall functional and cosmetic result.

●Facial skin defects most frequently can be closed with local flaps, using like tissue most often transferred as a random pattern transposition or rotational flap. Examples include local rhomboid flaps and V-Y advancement flaps (figure 3 and figure 4 and figure 6) [23,24]. Aesthetics are obviously of utmost import in the face, so choosing a local flap is usually best. This follows the principle of replacing like with like.

●Truncal defects are usually less dependent on aesthetics, requiring transfer of a larger volume of tissue while not negatively impacting function of the donor site or recipient site.

●Specialized areas such as the hands and feet also take judgment when selecting flap closure. The palmar and plantar skin are unique and difficult to replace. Most areas of the hands and feet require thin flaps to obtain the best functional results.

Evaluation of blood supply — Axial flap design requires identification of the appropriate vessel upon which the tissue transfer will be based.

In general, the vessel can be identified with a handheld Doppler, and the skin island required is usually centered over the vessel. Advanced imaging modalities such as magnetic resonance angiography and computed tomographic angiography have become more commonplace and delineate the anatomy of flap dissection in advance [25].

Perforator flaps require careful planning to reduce the risk of flap failure using preoperative mapping and localization of perforating arteries using a handheld Doppler [18]. In the operating room, the main perforator is generally identified by making a limited exploratory incision, with additional perforator dissection until the largest and best perforator is identified.

Management of donor sites — Defects that are created by harvesting a flap are managed by meticulous hemostasis and a primary closure. Skin grafting is rarely necessary.

The donor site is closed in layers to minimize postoperative wound dehiscence, and without tension on the suture line. Drains are used for larger wounds. Self-adhesive strips are applied to the suture line, followed by dry gauze, which is secured with a wrap bandage or adhesive dressing.

Physical activity is limited until the wound is healed to avoid rebleeding, hematoma, or dehiscence. Drains are used in donor site beds if the flap harvest disrupts lymphatic drainage, or if there is residual dead space. Drains are left in place until output is ≤30 cc/day.

If the donor site cannot be closed primarily, combined use of skin substitute with a split-thickness skin graft provides thicker coverage than a split-thickness skin graft alone without increasing morbidity. As an example, in a retrospective review of 80 patients undergoing a forearm free flap, the cohort treated with a skin substitute and split-thickness skin graft had superior cosmetic results (as judged by patients and surgeon) compared with patients undergoing a split-thickness skin graft alone [26]. Both groups had similar major and minor complication rates (18.8 and 15.0 percent, respectively). (See "Skin autografting".)

Identifying vascular compromise — Vascular compromise is the most common cause of flap failure. Poor flap design and failure to follow the angiosome concept of tissue blood supply can lead to partial flap loss if the flap includes too much tissue and extends beyond the anatomic boundary of the flap's blood supply. Vascular compromise can also occur due to twisting of the vascular pedicle during transfer of the flap to the recipient site. For free flaps, vascular compromise is usually due to thrombosis of either the artery or vein included in the microanastomosis. For total flap necrosis, the flap must be removed. For partial flap loss, the necrotic tissue requires debridement and local wound care. (See "Basic principles of wound management", section on 'Wound debridement'.)

Vascular compromise in pedicled grafts that is identified by color change and diminished capillary refill requires a return to the operating room to check for twisting of the pedicle and re-inset of the flap. In some cases, the flap must be temporarily returned to the donor site to allow for vascular recovery and flap reconstruction delayed.

For free flaps, the blood supply is similarly monitored by clinical observation evaluating the color, temperature, capillary refill, bleeding, edema, and appearance of the flap. Vascular compromise of free flaps necessitates prompt return to the operating room for evaluation of the cause and potential revision of the microanastomosis and flap salvage.

A simple Doppler unit is often used to evaluate arterial and venous signals in the flap and may improve flap salvage rates [27-29]. Using a tissue oximeter as an additional form of monitoring has gained favor and also appears to reduce flap loss [30]. In a series of 614 consecutive microsurgical flaps, 380 patients were monitored with clinical inspection and Doppler ultrasound alone, and 234 patients were also monitored with tissue oximetry [30]. Although tissue oximetry did not change the rate of re-exploration, flap loss decreased from 2.9 to 0.4 percent. When available, both Doppler ultrasound and continuous tissue oximetry should be used to monitor free flaps for the first three days after surgery. Monitoring is generally performed every 15 minutes for the first hour, every 30 minutes for the second hour, every hour for the next 10 hours, and then with routine vital signs every four hours.

Early recognition and intervention for vascular compromise of tissue flaps using other technologies has been assessed in observational studies using near-infrared spectroscopy to detect vascular compromise [31], as well as to improve monitoring and communication [32].

COMMONLY USED FLAPS — There are many types of flaps, all of which require specific knowledge of the vascular anatomy of both the recipient and donor site. It is beyond the scope of this topic to review all of the currently available flaps. Commonly performed flaps are presented briefly below.

Forehead flap — The forehead flap, which is used for nasal tip reconstruction, is the quintessential regional musculocutaneous flap. This flap is axial in its nature, based on the supraorbital and supratrochlear vessels, and includes some glabellar and frontalis musculature. The flap can be much longer than it is wide due to the axial nature of its blood supply, often reaching up into the hairline of the frontal scalp. Design of the flap is very important, using a template for the exact size of the nasal defect to be covered. This template is then transferred to the upper forehead skin centered over the axial blood supply. The flap is lifted in a submuscular plane, starting superiorly and working down toward the base. The flap can be carefully thinned distally prior to inset. Once elevated, the flap is transposed with a near-180° turn onto the nasal defect and inset with cutaneous sutures. The donor site is then closed in layers. This type of flap will often bridge over normal tissue and requires a secondary or even tertiary inset procedure to separate the base of the flap from the inset portion and to improve the aesthetic contour of the flap. These procedures are usually delayed until the initial edema and erythema have subsided.

Omental flap — The greater omentum is a peritoneal fold that drapes over the intestines, consisting of connective tissue, fat, and lymphatics. It gets its blood supply from the gastroepiploic vessels and will survive on either the right- or left-sided vessels [33,34]. Most commonly, the omental flap is transferred as a pedicle flap, but it can be used as a free tissue transfer (increasingly being used in lymphedema surgery).

Chest wall and chest cavity defects are often dealt with by omental flap transfer. Sternotomy wound dehiscence can be corrected with this flap, and empyema cavities can be filled with a large-volume omentum. With use in the chest, the most common complication is an upper abdominal or diaphragmatic hernia as a result of the transfer. This can be managed by transecting the pedicle a few months after transfer once the omentum has reestablished a blood supply and simply repairing the fascia or diaphragm.

The lymphatic-rich omental free flap can also be transferred to a lymphedematous upper extremity to improve symptoms. (See "Surgical treatment of primary and secondary lymphedema".)

DIEP flap — The use of free tissue transfer has become commonplace in breast reconstruction, with the deep inferior epigastric perforator (DIEP) flap most often used [8]. (See "Options for autologous flap-based breast reconstruction", section on 'Perforator flaps'.)

Though technically demanding and more time-consuming than pedicled flaps, perforator flaps have less morbidity at the donor site. The artery and vein are harvested with DIEP flap dissection as they perforate through the rectus muscle. The perforator is dissected free of the muscle, leaving all of the muscle behind, and as such, muscle function is preserved. Long-term studies have confirmed improved abdominal wall function in these patients when compared with pedicled TRAM flaps. Once dissected, the flap is transferred to the chest wall and the flap vessels are anastomosed to the internal mammary or thoracodorsal vessels as the recipients. Most arterial microanastomoses are handsewn with interrupted suture, while an anastomotic coupler is favored for the venous anastomosis [9].

TRAM flap — The transverse rectus abdominis musculocutaneous (TRAM) flap can also be used for breast reconstruction (picture 1). These were originally described as a flap based on the contralateral superior epigastric artery and vein, but the majority of these flaps are now transferred as ipsilateral flaps [13]. (See "Overview of breast reconstruction" and "Options for autologous flap-based breast reconstruction".)

The skin island includes the lower abdominal skin from just above the umbilicus to the suprapubic region, and the underlying muscle. With regard to blood supply to the skin, four zones (I to IV) are described. In planning the flap, one must take into account that zone IV and often zone II have poor blood supply, and the use of these areas should be avoided if possible. The anterior sheath is entered just above the pubis, the rectus muscle is transected, and the inferior epigastric artery and vein are ligated. The rectus abdominis muscle is then lifted out of the rectus sheath, with serial ligation of the intercostal neurovascular bundles as they are encountered. In the unilateral procedure, fascial-sparing incisions are possible, so closure of the abdominal wall defect can often be accomplished by primary repair without the need for mesh reinforcement. In the bilateral procedure, mesh repair is always required. Late abdominal bulging is more common in patients repaired with mesh compared with those closed primarily. A tunnel is made through the middle third of the inframammary crease. The flap is transposed into the defect and inset in the mastectomy defect. Repair of the harvest site is then accomplished, the abdominal wound is closed over drains in layers, and then the new breast mound is formed.

Anterolateral thigh flap — The anterolateral thigh flap is commonly used to provide additional coverage for the abdominal wall. Although the abdominal wall is an excellent source of flap material for local and regional repair, at times additional tissue is needed, such as following abdominal wall sarcoma resection or wounds that result from radiation treatment of cervical or prostate cancer.

The anterolateral thigh flap is based on a descending branch of the lateral femoral circumflex artery and has a large arc of rotation [35-37]. A limited arc can occur in some patients with a low takeoff of the vessel. The flap is commonly found to be septocutaneous; however, in some patients the perforator artery and veins traverse muscle and an intramuscular dissection is required.

Donor site morbidity, including skin separation and lymphocele, are recognized complications of flap harvest.

Radial forearm flap — The radial forearm flap is often used when there are exposed tendons or bone following trauma, infection, or surgical extirpation. This flap can also be transferred as a reverse flow flap if the patient has an intact palmar arch allowing coverage of the hand up to the metacarpophalangeal joints either on the dorsal or palmar surface.

The radial forearm flap is an axial flap that can be raised as a fasciocutaneous flap, a fascia-only flap, or even an osteocutaneous flap (portion of the distal radius included) [38,39]. It is based on the radial artery and the venae comitantes, though often superficial veins are included in the flap elevation to improve venous outflow.

Dissection of the flap pedicle is relatively simple, following the path between brachioradialis and flexor carpi radialis with care to avoid radial nerve injury while elevating the flap.

Donor site morbidity can be a problem with flaps that include skin since the donor site will usually require a skin graft for closure. This problem led to increasing use of a fascia-only flap, which allows primary skin repair at the donor site but requires skin grafting at the wound site instead.

Medial gastrocnemius flap — One of the earliest described muscle flaps is the medial gastrocnemius flap. This flap is based on the medial sural artery and vein. The most common uses are salvage of total knee replacement and coverage of compound tibial fractures. (See "Surgical reconstruction of the lower extremity".)

The flap is elevated through a medial incision adjacent the tibia. This incision can be entirely separate from the recipient site, or, often, it connects to the recipient site at its most inferior aspect. The muscle is elevated from distal to proximal starting at the junction of the middle and distal third of the calf, taking care not to injure the Achilles tendon. The insertion site of the Achilles is transected, and the flap is lifted out of its bed. Dissection then proceeds proximally, releasing the muscle from all surrounding fascial attachments. The vascular pedicle enters the muscle high in the calf, just posterior to the knee joint, and is usually not formally dissected during flap elevation.

The arc of rotation of this flap will cover the distal thigh down to the middle third of the calf. The transposition of the flap can be limited by the muscle fascia. This can be improved by scoring or removing the muscle fascia at the time of transfer. Following inset of the flap into the defect, a split-thickness skin graft can be applied. A negative pressure wound dressing is used to hold the skin graft in place. The knee is immobilized for two to four weeks while the flap and overlying graft heal.

FUTURE DIRECTIONS — In addition to prefabricated and prelaminated flaps, an exciting new frontier in flap and reconstructive surgery is the creation of bioengineered flaps [40,41]. The construction of such flaps is similar to the other efforts underway in tissue and organ transplantation (eg, modified pig heart). Fabricating bioengineered flaps is a complex undertaking, requiring knowledge of each component of the tissue to be engineered, including oxygen requirements.

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Flap surgery (The Basics)")

SUMMARY AND RECOMMENDATIONS

●A flap is a transfer of tissue with its blood supply from one part of the body to another. The blood supply to a flap is persistent and does not depend on the recipient bed. A flap is the best approach to wound repair when primary repair is unobtainable, the wound bed is not amenable to grafting, or the aesthetics are unfavorable for grafting. (See 'Introduction' above and 'Principles of reconstruction' above.)

●In general, flaps for reconstruction are classified based upon the type of blood supply (ie, random, axial), proximity of the donor tissue to the recipient (ie, local, regional, distant), and tissue composition (eg, musculocutaneous, fasciocutaneous). Flaps can also be further classified based upon how the donor tissue is transferred into the recipient tissue defect (eg, rotation, advancement). (See 'Flap nomenclature' above.)

●Flap selection begins with an analysis of the defect location, vascularity of the defect bed, comorbidities, cosmetic significance, and functional significance. As a general rule, simpler local and regional flaps are used if possible. More complicated flaps, such as distant pedicled or free flaps, are used if simpler options are not available or if a distant flap will give a better overall functional and cosmetic result. (See 'Flap selection and donor site evaluation' above.)

●Vascular compromise is the most common cause of flap failure. Vascular compromise can occur due to twisting of the vascular pedicle during transfer of the flap to the recipient site. For free flaps, vascular compromise is usually due to thrombosis of either the artery or vein included in the microanastomosis. When available, both Doppler ultrasound and continuous tissue oximetry should be used to monitor free flaps for the first three days after surgery. (See 'Identifying vascular compromise' above.)