Categories

Decades of research, clinical and surgical experience as well as better knowledge of vascular anatomy have allowed the classification of flaps. The most commonly used categories are based on:

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  type and anatomy of vascular supply (ie, source vessel)

  
  
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  method of tissue transfer (ie, technique of flap elevation and movement)

  
  
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  flap composition (ie, tissues that constitute the flap).

Classification according to the type of vascular supply

McGregor and Morgan [14] categorized flaps as random skin flap or axial pattern skin and/or muscle flap. Random pattern flaps lack a specific blood supply for their vascular pattern and are subject to restrictions in length. They must, therefore, correspond to a certain width-to-length ratio (chapter 10.4). This ratio depends on the dermal and subcutaneous vascularity (chapter 2.2). Axial pattern flaps have at least one specific, direct vascular pedicle that contains an anatomically recognizable arteriovenous system, including lymph vessels, and a nerve within the long axis of the flap (chapter 10.4, 10.5). A well-defined axial pedicle can safely perfuse a flap beyond its angiosome (chapter 2.2.3), ie, with a width-to-length ratio larger than 1:2–1:3, and is therefore more reliable in comparison to a random pattern flap. The pedicle consists of a vascular branch, originating from a source vessel, allowing it to be isolated in a specific flap. Such a vascular tree of source vessels of the lower extremity is described in ( Fig 10.3-1a–b ).

At the level of the groin, the inguinal ligament constitutes an anatomical barrier for a network of deep and superficial vessels emerging from the external iliac artery, and common femoral arteries provide a variety of source vessels more distally. The deep inferior epigastric, circumflex iliac, and external pudendal arteries emerge proximally, above the inguinal ligament, whereas their superficial counterparts branch off below the inguinal ligament with common or separate origins. These vessels supply the region of the groin, the iliac crest, and the abdominal wall offering different options for flaps. Dorsally, the superior and inferior gluteal arteries are the major vessels for gluteal muscle and skin perfusion. The inferior gluteal artery runs down the posterior aspect of the thigh, sometimes as far as 8 cm from the popliteal fossa.

While the vascularization of the thigh rarely poses a problem for wound healing in comparison to the lower leg, preservation of the medial and lateral femoral circumflex arteries, as well as branches of the deep femoral artery may be important as they may all serve as pedicles for many useful flaps. The superficial femoral artery gives off muscle branches and the superior genicular artery at the adductor hiatus. This forms a rich anastomotic network with the inferior genicular artery arising from the popliteal artery and terminating distally as the saphenous branch running with the homonymous sensitive nerve. Before bifurcating into the tibiofibular trunk and the anterior tibial artery, the popliteal artery gives off paired sural arteries, which supply the two heads of the gastrocnemius muscles, another potential source for a flap pedicle for the area of the knee. The anterior tibial artery passes over the interosseous membrane, courses distally into the anterior muscle compartment of the leg surrounded by the tibialis anterior and extensor hallucis muscles anteriorly and the interosseous membrane posteriorly to become the dorsalis pedis artery of the foot. Source arteries and their concomitant veins usually travel adjacent to—but not within—the rigid fascial envelopes, in loose connective tissue, often containing fat that helps to identify these structures. The deep fibular nerve joins the anterior tibial artery in the proximal third of the leg. Posterior to the interosseous membrane, the tibiofibular trunk divides into the fibular and posterior tibial artery. The fibular artery runs medially to the fibula between the posterior tibial and flexor hallucis longus muscles. It supplies the fibula and the overlying skin through septocutaneous vessels and forms the vascular basis for the fibula flap. Its terminal branch, the lateral calcaneal artery, may serve as an important pedicle for local flaps for soft-tissue defects in the region of the ankle. In spite of the nomenclature, neither the superficial nor the deep fibular nerve runs parallel to the fibular artery. The posterior tibial artery gives off branches to supply muscles, then bifurcates into the medial and lateral plantar arteries after the distal margin of the flexor retinaculum muscle and runs parallel to the tibial nerve, which in turn is responsible for plantar sensation and intrinsic foot-muscle innervation distally. The medial plantar artery and the respective nerve supply the instep area, which provides a valuable reservoir of skin for reconstruction of the heel.

For reconstructive surgery of the upper extremity and other locations of the body, the same anatomical knowledge is required.

In addition to the knowledge of the normal anatomy of the arteries and veins and possible variations of leg perfusion, these causes for critical changes have to be taken into consideration, both, when dealing with emergency cases as well as in planning elective surgery:

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  peripheral artery occlusive disease

  
  
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  diabetes mellitus

  
  
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  posttraumatic changes.

The exact knowledge of vascular anatomy is important, especially in regard to flap elevation, but also to surgical approaches, in view of salvage operations such as reoperations or prosthetic joint replacement, and/or tissue transfer. For reconstructive surgery of the upper extremity and other locations of the body, the same anatomical knowledge is required. According to their blood supply, muscles have been divided into five different types ( Fig 10.3-2a–e ) [15]:

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  • Type 1: a single major pedicle

  
  
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  Type 2: one major pedicle and minor pedicles

  
  
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  Type 3: two major pedicles

  
  
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  Type 4: several segmental pedicles of approximately the same size

  
  
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  Type 5: one dominant pedicle and secondary segmental pedicles.

Classification according to the type of transfer

Local skin flaps are used to close defects immediately adjacent to the donor site and are classified according to the respective technique of transfer (chapter 10.4):

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  Advancement: advances along the long axis of the flap, from the base towards the defect. V-Y advancement is a modification of the advancement flap.

  
  
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  Rotation: rotation about a pivot point into the defect

  
  
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  Transposition: rotation about a pivot point into the defect with lateral movement

  
  
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  Interpolation: rotation about a pivot point into the defect that is nearby but not directly adjacent to the donor site, so that its pedicle must pass over or under the intervening tissues.

Regional flaps have the base of their pedicle in contiguity with the defect and the skin on the same extremity (chapter 10.5). If the pedicle consists of the vascular bundle only, without subcutaneous tissue and skin, the flaps are called island flaps.

Distant flaps are required when the recipient site or tissue defect is not in close vicinity to the donor site or because there is no healthy soft tissue adjacent to the wound. They are divided into two categories:

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  attached direct distant flaps

  
  
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  free flaps (ie, supplied by microvascular anastomosis) (chapter 10.6).

The expression “attached direct distant flaps” rightfully implies that flaps from a distant donor site are temporarily attached to the area of the defect. For example, the patient has an open-wound defect on the lower leg or the palmar side of a finger that requires soft-tissue coverage. The donor site for the distant flap will be chosen from the contralateral leg, respectively the dorsum of the neighboring finger. Therefore, the patient′s injured lower leg or finger must initially be attached to the contralateral leg or neighboring finger, using a cross-finger or cross-leg flap. After a period of about 2–3 weeks (cross-finger flap) or 3–4 weeks (cross-leg flap), vessels from the surrounding tissues of the recipient site grow into the flap, whereby it gradually becomes less dependent on the circulation of the donor site for survival. The flap is then separated from the donor site and, will survive in the new surrounding of the original defect. This technique not only takes several weeks to complete, it is also cumbersome and inconvenient for the patient. Today, this method will rarely be considered for the leg, only if no other options are available. For finger injuries, however, this technique should be part of the surgeon′s armamentarium.

Free flaps, ie, flaps with an axial pattern-type of blood supply were developed to circumvent the disadvantages inherent to attached direct distant flaps. Free flaps along with their pedicle are completely detached from the donor site and are transferred within one procedure to the recipient site. After microsurgical anastomosis, blood flow is reestablished (chapter 10.6). Free flaps undergo a certain period of ischemia during the procedure until they are reperfused, which is, however, usually tolerated by the tissues.

Lately, techniques in flap surgery have been developed with the specific intention of optimizing reconstructive goals. Accordingly, it is possible to prefabricate, respectively prelaminate a flap prior to transfer. Prefabrication refers to the implantation of a nonnative vascular pedicle into the tissue desired for reconstruction before its actual transfer [16], whereas prelamination refers to the implantation of anything else into the future flap [17].

Classification according to tissue composition

Flaps may consist of any type and number of tissues in virtually any combination. Complexity of the defect, vascularization of the recipient site, constitution of the tissues needed, donor-site morbidity as well as patient-related factors will dictate which type of flap should be used. Composite flaps often incorporate skin, muscle, bone and the intervening subcutaneous fat and fascia, allowing single-stage reconstruction of complex defects. Specialized flaps can provide sensory skin and functional muscle to areas requiring special needs.

The three varieties of flaps (ie, type of vascular supply, technique of transfer, and tissue composition) require a proper terminology and classification that is of paramount importance not only in teaching basic knowledge about flaps, but also in daily practice. This allows the development of algorithms and treatment strategies using a large number of new flap options that are often technically demanding. Despite widespread classification systems, these often do not cover all aspects of a flap. There have been various attempts to provide a more comprehensive classification system [18, 19] ( Table 10.3-2 ). One of these systems de scribes the circulation (vascular supply, axial pattern versus random pattern) as the core characteristic, and constituents, contiguity, construction, conformation and conditioning of the flap as further characteristics that determine flap nomenclature. These characteristics are also called the six “C”s.