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These early flaps were largely thought to be based on “random”
blood supply, which limited the size and scope of successful flaps.
Large flaps went on to either partial or complete flap necrosis and
flaps were designed with the tenet that the length could not be
greater than 1.5× the width. In the 1960s and 1970s, the work of
Milton on porcine skin flaps demonstrated that known blood vessels
can support long narrow skin flaps3 and was supported by the work
of McGregor, who described both the forehead flap and the groin
flap.4 Axial skin flaps fell by the wayside as flaps based on muscles
grew in popularity. This was reinforced with the development of the
operative microscope in the 1960s, and free muscle and skin/muscle
flaps seemed to offer a flexible solution for most reconstructive
problems. Muscle flaps proved to be a reliable workhorse and were
seemingly endless in sources across the body. However, the
morbidity of muscle deficit in the donor site as well as unsightly
muscle bulk at the recipient site led innovative surgeons to opt for
perforator flaps based solely on an artery perforating through the
muscle to the skin.5-7 This made it possible to leave the muscle
intact in the donor site with preserved innervation and vascular
supply.
FLAP NOMENCLATURE AND CLASSIFICATION
The system by which flaps have come to be named and classified
seems to follow the nebulous and fluid nature of plastic surgery itself.
Some flaps are named after the region of the body from which they
are harvested, such as an anterolateral thigh flap, whereas some
flaps are named after their blood supply, like a deep inferior
epigastric artery perforator flap. To further confuse the surgeon,
classifications are frequently overlapping. Nonetheless, the
vocabulary to describe flaps is necessary to help guide flap selection
as well as facilitate communication with other medical professionals.
Overall, flaps are named and classified by a few core characteristics
that also guide flap design and selection: flap content, blood supply,
method of transfer/movement of the flap, and manipulation.
Flap Content
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The plastic surgeon’s mantra is to “replace like with like.” As such,
assuming the patient has no comorbid factors that would steer the
surgeon’s decision, the first step toward flap selection is an
evaluation of what is missing in the defect (skin, functional muscle,
bone, cartilage, fascia). Flaps are similarly classified by what tissues
are included. When selecting flaps, they should be designed to
include the necessary tissue to best replace what has been taken.
Flaps can thus be classified based on what tissues they include.
Some of the simplest flaps contain only skin and the subcutaneous
tissue, which are termed cutaneous flaps. Selection of cutaneous
flaps generally considers skin quality, thickness, and hair-bearing
status to match the surrounding skin. Taking fascia with the skin and
soft tissue then categorizes the flap as a fasciocutaneous flap. The
inclusion of fascia improves the vascularity of the flap through
inclusion of the prefascial and subfascial plexus. Fascial flaps or
adipofascial flaps can be raised without the overlying skin and offer
thin flaps that can be skin grafted and are easily contoured to even
complicated anatomical topography. A temporoparietal fascia flap for
ear reconstruction is a good example of this concept, as the fasciaonly flap is pliable and thin enough to display even the nuanced
topography of an ear.
Muscle flaps harvest muscle with its blood supply. If these are
harvested with the overlying skin, they become myocutaneous
flaps. As mentioned before, given the abundance of option and
consistency in vascular supply, muscle and myocutaneous flaps are
a workhorse of reconstructive surgery and have been extensively
studied. In 1981, Mathes and Nahai formulated what is now the
accepted classification of muscle flaps based on the type of vascular
supply, which will be discussed later in this chapter. Dynamic muscle
flaps can also be harvested to provide volitional movement to an
area where muscle or nerve has been sacrificed. Temporalis muscle
can be transferred regionally to provide dynamic smile
reconstruction. Innervated free gracilis muscle flaps can be
harvested with their branch of the obturator nerve to provide dynamic
muscle all over the body including smile or forearm reconstruction.
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If the defect has a large segment of missing bone, flaps containing
bone may be needed to provide structural support. These are known
as osseous flaps. Fibula flaps based on the peroneal artery are a
common source of vascularized bone for head and neck bony
reconstruction as well as numerous other sites around the body.
When additional soft tissue is needed, osteocutaneous flaps ,
which include a skin paddle, or osteomyocutaneous flaps , which
contain skin and muscle, can be harvested.
More recently, flaps that carry lymphatic nodes and vessels have
been designed to help treat regions where lymphatics have been
disrupted. These are known as vascularized lymph node transfers
and can be effective in treating lymphedema. Omental flaps are a
source of vascularized lymph node transfer.
8
Blood Supply
The great Sir Harold Gillies once said, “Plastic surgery is a constant
battle between blood supply and beauty.”9 In accordance with Gillies’
statement, knowledge and understanding of flap blood supply will
help guide flap selection to ultimately maximize the esthetic outcome
of both the recipient and donor site. For cutaneous flaps, the blood
supply is generally categorized into random or axial. Random
pattern blood supply lacks a known arterial vessel and is based on
the subdermal plexus for perfusion (Figure 4.2). Without a more
robust blood supply, traditionally these flaps have been designed to
be no longer than three times the width of the base of the flap, or the
so-called 3:1 rule. Axial flaps carry a known arterial blood supply,
generally along its longitudinal axis (Figure 4.3). The size of an axial
flap is limited only by the vessel’s angiosome, which is the territory of
tissue that is supplied by a vessel.10 Axial flaps can be further
subdivided into perforator flaps. If we consider the random blood
supply of the subdermal plexus to be the most microform of blood
supplies to the skin and an axial vessel to be the most macroform,
then a perforator flap that is based on a single perforating vessel
from an axial vessel is somewhere in the middle. The concept of an
angiosome can then be applied to perforator flaps, and the maximum
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flap size based on a perforator then becomes a perforasome, which
is the territory of tissue supported by that perforator (Figure 4.4).
11
FIGURE 4.2. Dermal plexus blood supply. (From
Blausen.com staff (2014). Medical gallery of Blausen
Medical 2014. WikiJ Med. 1(2).
doi:10.15347/wjm/2014.010.)
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FIGURE 4.3 Nasal reconstruction with an axially based
nasolabial flap (A , “before”; B , “after”).
FIGURE 4.4. Representation of the angiosome and
perforasome concept. All of this skin would be supplied by
one angiosome, and each color represents the skin
supplied by one perforasome.
Flaps carrying different tissues have different blood supply
classifications. Bringing fascia with a flap inherently increases the
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blood supply, as was discovered by Ponten in 1981.12 The blood
supply of fasciocutaneous flaps subsequently underwent numerous
iterations of classification. These flaps were initially classified by
Cormack and Lamberty in 1984 based on the pattern of
vascularization from the perforators.13 In 1986, Nakajima grouped
them based on the path and tissue that the perforator traveled to
reach the skin.14 In modern discussion, these groups are generally
simplified into direct cutaneous perforators, which carry a direct
pedicle to fascia and skin; septocutaneous perforators, which travel
through a muscular septum without entering the muscle itself; and
musculocutaneous perforators, which traverse a section of muscle
before reaching fascia/skin (Figure 4.5).
FIGURE 4.5 Perforator types: Purple: Direct Cutaneous
perforator; Blue: Musculocutaneous Perforator; Green:
Septocutaneous Perforator.
Muscle flaps usually can have variable types and sizes of vessel
supplying them. They are classified by not only the type of blood
vessel supplying them but also whether the vessel can support the
entirety of the muscle flap. This classification was first developed by
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Mathes and Nahai in 1981 (Figure 4.6) and is still widely used
today.
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FIGURE 4.6 Mathes and Nahai classification of muscle
vasculature. Type 1: One vascular pedicle; Type 2: One
dominant vascular pedicle, one minor pedicle; Type 3: two
dominant pedicles; Type 4: segmental vascular pedicles;
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Type 5: One dominant pedicle and secondary segmental
pedicles.
Broadly speaking, the blood supply of any flap can be categorized
as pedicled or free. A pedicled flap remains attached to its vascular
supply. For pedicled flap selection, it is crucial for the reconstructive
surgeon to accurately estimate the reach of any given flap; the last
thing any surgeon wants to encounter in the operating room is a
well-raised flap that does not adequately reach the defect. For flaps
in general, the more isolated the vascular pedicle is from its
surrounding soft tissue, the greater the freedom of movement of the
flap. When this concept is carried to the extreme, the flap can be
taken as a free flap , which has a transected blood supply which is
then anastomosed to a new blood supply near the recipient site.
Provided there is a recipient vessel, free flaps offer great flexibility in
not only movement but also donor site choice, as the surgeon is no
longer limited by the reach of a flap.
Classically, flaps are always raised based on anterograde arterial
flow; however, certain flaps can be based on reverse or retrograde
flow. A common example of this is the reverse radial forearm flap,
which is based on flow from the ulnar artery across the palmar arch
and then retrograde up the radial artery (Figure 4.7).
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FIGURE 4.7. A reverse radial forearm flap based on
retrograde flow across the palmar arch. A. Defect; B.
Designed on flap on volar forearm; C. Elevated flap; D.
Inset flap.
The blood supply of a flap can also be altered to be more robust
and for a greater amount of tissue to be harvested. One of the oldest
techniques is the delay phenomenon. The delay phenomenon
occurs when a sublethal amount of ischemia is applied to the flap,
typically through partial elevation and division of a portion of the
blood supply, which then stimulates dilation of the remaining blood
supply and preconditions the flap to ischemia. A delayed flap can be
useful when there is concern for the ultimate perfusion of the flap. A
well-studied example of this is the increased success in pedicled
transverse rectus abdominis myocutaneous (TRAM) flaps when the
superficial and deep inferior epigastric arteries are ligated at a
preliminary stage, forcing the flap to survive on the superior
epigastric vessels.
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