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together, these facts explain the clinical observation that fullthickness grafts are more difficult to achieve reliable take.15 Wound
conditions must approximate the ideal and a longer timeline is
expected for consistently good results.
Split-thickness grafts, on the other hand, will more readily take
even in more adverse wound conditions. By virtue of including only a
variable quantity of superficial dermis, these grafts have low
metabolic demand and relatively abundant vascular tissue. At the
donor site, retained follicular and adnexal structures enable healing
by budding epithelialization.25 Take is enhanced by the relative ease
of plasmatic imbibition from the underlying wound bed that permits
graft survival until true angiogenesis has occurred days later.10 This
method of skin grafting is readily applicable in virtually all areas of
the body and is limited mainly by the tendency of these grafts to
undergo secondary contraction in the months following initial take.
Donor sites can be anywhere that has relatively flat planes of skin for
harvesting, most commonly the anterior, lateral, and posterior thighs,
the posterior trunk, or the abdomen; prior split-thickness donor sites
may be reused for serial grafting.
6
The Patient
The discussion of patient-level factors that influence skin graft take
could fill an entire tome. For this discussion, we will consider a few of
the most important modifiable elements. Smoking, which historically
referred to tobacco smoking but now includes marijuana, electronic
cigarettes, vaping, and related forms of inhalational recreation,
shares two common features that work against the process of take:
oxidative stresses and endothelial dysfunction. Patients should be
counseled on the tremendous upside of eliminating these habits prior
to graft reconstruction. Extrapolating from the best available data,
many surgeons recommend 7 to 10 days of abstinence before
surgery and at least 2 weeks after surgery, though this has not been
rigorously studied.26 Congestive heart failure should be optimized
medically prior to skin graft reconstruction as this has been shown to
be associated with poor graft take.27 Other patient-level morbidities
to be particularly aware of are transplant-related
immunosuppression, elevated body mass index above 30 kg/m2, and
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peripheral vascular disease, particularly in the presence of venous
stasis sequelae, when considering lower extremity skin grafting.27 Of
course, many other factors may be important as well and need to be
assessed on a case-by-case basis.
The Timing
Skin is the largest organ in the human body, and it serves many
essential functions such as sensation, thermoregulation, protection
against insensate fluid losses, antibacterial defense, and mechanical
fortification. When skin integrity is compromised, through surgical
insult, trauma, vascular disease, or any other destructive etiology,
essential physiological homeostasis may suffer.6 Given these factors,
an urgency may be felt to apply skin grafts. Donor site
considerations may strengthen the argument for a more deliberative
approach. Skin substitutes and dressings such as negative-pressure
wound therapies now serve as bridges through time to optimize the
wound and patient factors. For example, a “wait-and-see” approach
may be applied to evaluate wounds over time for appropriateness
and readiness for definitive management with skin grafts or
substitutes.
The need for a vascularized wound bed for skin grafting leads to
the clinical conundrum of when to subject a patient to skin graft
surgery at all, incurring a donor site which itself must heal and add to
the metabolic burden, given that vascularized tissue beds will likely
heal over time by secondary intention. These issues are particularly
relevant given the risk of donor site morbidities including pain,
pruritus, infection, hyperpigmentation, and hypertrophic scar.
6,28
The
earlier restoration of protective skin functions may be used as a
justification for skin grafting to wounds that would otherwise heal, but
slowly because of the size of the wound or tenuous nature of present
blood supply. However, patients with comorbidities indicating poor
ability to heal, such as low protein levels, immunosuppression, and
poorly controlled diabetes, may need careful relative risk
assessment, including potential for donor site healing delay and
concomitant increased wound burdens. Potential for multiple
surgeries must also be factored into the decision-making process.
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TECHNIQUES
Wound Bed Preparation
All instances of skin graft reconstruction must begin with a habile
assessment of the wound for the factors discussed above. Specific
recommendations based on our experience include the following:
Serial debridement if there is concern for ongoing tissue loss
at the periphery of the wound. This is especially important for
wounds that extend to the level of adipose tissue as interval
examination often demonstrates previously healthy appearing
tissue that has since demarcated as nonviable. Aggressive
debridement of questionably viable tissue will help limit the
incidence of graft loss.
Iterative washouts for presumed or known infection can be
indispensable in minimizing infection, especially in cases of
wounds arising from necrotizing soft-tissue infections. Certain
particularly virulent organisms such as Pseudomonas
aeruginosa, Staphylococcus aureus, Streptococcus
pyogenes, and others may require special consideration.
Satisfactorily rule out musculoskeletal infections prior to
reconstruction. Bone cultures are the standard to rule out
osteomyelitis, but liberal utilization of magnetic resonance
imaging, computed tomography with single-photon emission
series, and three-phase bone scans can all have a role as
noninvasive modalities too.
29
If malignancy is possibly harbored within the wound, obtain
surgical biopsy and defer management until after definitive
pathologic analysis.
Even healthy appearing wound beds with beefy red
granulation tissue benefit from superficial debridement. There
is a substantially greater bacterial count in the most superficial
millimeter or so of granulation tissue compared to deeper
tissue, so tangential debridement, such as curettage, provides
the optimal wound bed.
30
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Graft Harvest
As the adage goes, it pays dividends to measure twice and cut once.
Any graft harvest begins with an accurate measurement of the
wound to be grafted. A flexible ruler is most useful to accomplish
this. Instead of measuring a regular polygon, we recommend first
measuring the largest dimension of the wound and then the next
largest dimension; trying to measure a Cartesian length and width
only works well in roughly rectangular wounds. For particularly
irregular wounds, dividing the defect into smaller component wounds
that can be readily sized for surface area with the ruler is handy. For
these smaller component wounds, visualizing as either rectangles or
triangles facilitates graft harvest, which occurs in rectangular strips
(Figure 6.2).
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FIGURE 6.2 Wound envisioned as geometric pattern to
facilitate skin graft donor site measurement and
preparation.
Defects confined to the dermis have negligible depth and can be
measured purely as surface area. However, those that extend into
the subcutis and even down to the deepest structures do have a
material depth component that must be accounted for; wounds
deeper than 1 cm should have some adjustment made to ensure
adequate coverage of the walls of the three-dimensional wound. A
good heuristic for estimating how much extra graft to take is to
measure the depth of the wound in centimeters and add that number
to the measurement of the longest dimension of the wound. This will
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often facilitate adequate skin harvest without an unnecessarily large
donor defect.
Once the graft size is established, prepare the donor site with local
anesthetic. There are many options, but we have found bupivacaine
with epinephrine to be helpful for both immediate postoperative
analgesia as well as hemostasis after graft harvest. This local
anesthetic solution is injected as an infiltrating solution beyond the
borders of proposed graft harvest. At least 10 minutes elapses from
injection to harvest, because time frames shorter than this enable
the vasodilatory effect of the amide anesthetic to take hold but not
the vasoconstricting effect of the epinephrine, which is slower
onsetting.
31
Full-Thickness Grafts
For full-thickness graft harvest, a template of the wound is obtained,
usually with a medium such as the discarded sterile suture foil or the
thin sterile paper from the surgical gloves. Carefully mark the
dimensions of the wound on the medium and transfer to the intended
donor site. Adjust the markings to formulate a roughly lentiform
shape, which is necessary for primary closure of the donor site. With
tension applied both perpendicular and parallel to the direction of
skin harvest, a sharp knife is used to elevate the dermis-epidermis
unit from the underlying adipose tissue just deep the reticular dermis
at the level of the subdermal plexus, trying to leave as little adipose
tissue on the graft as possible. We cannot overemphasize the need
for firm, constant tension, and counter tension during this process.
For larger grafts, it may be necessary to switch to a fresh blade
periodically, too. Once the graft is harvested, all parasitic fat should
be sharply excised from the deep aspect of the graft using iris
scissors as the graft is draped off the surgeon’s finger with
counterweights such as clamps, carefully applied to avoid undue
damage to the graft. Afterward, a saline-moistened gauze can
protect the graft from desiccation until it is ready for insetting. The
donor site is usually closed primarily, often necessitating some
amount of undermining and, occasionally, resection of intervening
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adipose tissue to reduce tension on the closure. We recommend a
layered closure to prevent scar spreading.
Split-Thickness Grafts
Split-thickness grafts can be harvested in a variety of ways. Probably
most common in modern practice is to use either a Humby knife
(almost always with the so-called Watson modification) or a powered
dermatome. We recommend a similar regimen of bupivacaine and
epinephrine administration prior to graft harvest, but in this instance,
we believe that a greater volume of infiltration is helpful. Total volume
should keep the patient’s mass and maximum safe dose of local
anesthetic in mind but need not reach tumescent volume such as in
liposuction. Usually 50 to 100 mL total is effective, and the
anesthetic can be diluted with injectable saline as needed for
volumetric purposes. Increased tissue turgor makes the skin firmer
and better able to push back against the blade of the harvesting
apparatus, permitting a consistent thickness, especially over the
larger dimensions common for split-thickness harvests.
Wound dimensions should be double-checked and an appropriate
cutting guard selected to meet the graft morphologic needs. Guards
commonly come in increments of 1 in, ranging from 1 to 4 in. In
practice, the 4-inch guard can be difficult to use and get a full 4
inches of width, so many surgeons consider 3 inches the maximum
width to be used. The thickness should be checked and rechecked
depending on the desired graft. Those with a thickness of 8/1000 of
an inch are considered epidermal grafts, those from 10 to 18/1000 of
an inch are typical split-thickness (12/1000 is our preferred splitthickness setting), and those 20/1000 or more are functionally
equivalent to full-thickness grafts. Keep in mind that these are
approximations, and the true thickness of the dermis will differ based
on patient and anatomic considerations. Consider confirming that the
mechanics of the harvesting tool match the expected settings. Once
the thickness is set, the entire apparatus, either Humby knife or
powered dermatome, and the marked skin should be lathered in
lubrication such as mineral oil.
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Penetrating towel clamps used at the corners of the marked graft
provide an assistant-sustained countertraction and keep the skin
planar for a safe harvest. If a powered dermatome is being used, the
operator then approaches the skin at a 45° angle and allows the
blade to enter the dermis to the maximum depth that has been set.
Once the initial cut is made at 45°, the angle of incidence should be
reduced to virtually parallel while firm yet consistent pressure is
applied to the cutting end of the dermatome. Force should be
transmitted through the dermatome to advance it, effectively raising
the graft for the desired distance. Approaching the end of the marked
area, the dermatome should “take off” like an airplane, severing the
graft and completing the harvest. The dermatome should be
powered on through engagement of the skin and release from the
skin. If a Humby knife is used, similarly enter the dermis at a 45°
angle, then, using gentle to side-to-side motions, advance the blade
in a parallel fashion to the dermis, raising the graft as the blade is
moved along. Termination of the graft involves angling the blade
superficially.
If the graft is not immediately needed, it can be kept in a bowl of
sterile saline or in a saline-moistened surgical gauze.
To Mesh or Not to Mesh
Unmeshed skin grafts, often called “sheet grafts,” are more strongly
indicated in cosmetic areas because of the potential for pebbled
scarring from the secondary intention healing in the interstices of
split-thickness skin grafts. They may also heal more quickly, ending
the inflammatory phase of wounds because of the absence of the
interstices.32 Decreased contracture by secondary healing may also
lead to use in areas of greater mobility, such as across joints.
32
However, the absence of significant fenestration increases the risk of
fluid accumulation, impairing revascularization and leading to graft
failure.32 “Pie-crusting” is often performed, for example, using an 11
blade to create small slits for fluid egress. Conversely, meshing
allows for expansion of the graft to cover a larger area with a smaller
donor site, more contourability to the wound bed, and decreased risk
of fluid accumulation leading to graft loss,6 but the resultant scar is
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dramatic and characteristic. The process of reepithelialization in
areas without skin graft occurs from the wound periphery.8 This tenet
supports meshed skin grafts healing more quickly than large wounds
because the distance the reepithelialization must cover is drastically
reduced.
Graft Insetting
Prior to inset, the wound bed should be checked for bleeding. Even
small oozing points can produce consequential hematoma that will
prevent firm adherence of the graft and eventually cause necrosis of
the grafted skin. The skin graft should be applied to the wound with
careful attention to the orientation as there is a polarity of the skin.
The dermis is typically pale and less shiny with the epidermis
appearing like other, unharvested skin from the patient. The dermis
side should always be positioned on the deep aspect of the wound.
Position the graft to align one edge with the wound bed and place
either a suture or staple here; we mostly use absorbable suture such
as chromic gut. From this point, carefully orient the rest of the graft,
sewing or stapling as you proceed. Trimming of any excess can be
performed with sharp scissors and the scraps of skin saved as a
precaution until the wound is fully covered. Quilting sutures may
assist in contouring to deep or irregular wound beds. For fullthickness grafts, prior to placing the final sutures, two more steps are
necessary. First, flush the wound bed below with sterile saline and
ensure that there is no hematoma collecting. This step is not
necessary for split- thickness grafts as the translucency permits direct
visual confirmation of no hematoma. Second, carefully use the
scalpel or sharp scissors to introduce small cuts in the graft, “piecrusting,” to permit fluid efflux as the graft heals. A more recent
advancement has been the avoidance of all sutures and staples for
graft fixation and instead utilization of fibrin-based tissue adhesives
to anchor the graft in place.
Dressings
The dressing overlying the skin graft plays an essential role in the
success of the tissue transfer. Immobilization to reduce shear forces
and gentle, even pressure, to ensure approximation of graft to
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recipient site without fluid collections, are mainstays of
recommended dressings. Bolsters are almost invariably used as a
means of providing even pressure across the surface area of the
graft, aiding in anchorage via wound bed fibrin, eliminating potential
spaces where blood can accumulate, decreasing exposure to shear
forces, and maintaining a clean or even sterile environment to
reduce the probability of infection. At times, more general
immobilization, of joints, for example, must also be considered.
Historically, a tie-over bolster was used for all skin grafts. There is
still a role for this method in contemporary practice, but it is mainly
limited to smaller grafts used in the head and neck region. To
construct a tie-over bolster, silk sutures are placed around the
perimeter of the graft after it has been sewn or stapled in place. The
sutures are arranged to be diametrically opposed in pairs for
eventual knotting. A large piece of petroleum impregnated gauze is
then placed over the graft with adequate excess to accommodate
sterile cotton balls soaked in povidone-iodine or mineral oil to be
placed on top of the gauze and then wrapped up and covered. The
silk sutures are then tied over this bundle of petroleum gauze and
cotton balls, which will act to hold the gentle pressure on the bolster.
This will stay in place for 5 to 7 days, most often.
For most other grafts, negative-pressure wound therapy is the
preferred bolstering technique. Numerous studies in the 21st century
have shown the negative-pressure therapy provides substantial
benefit in terms of improved graft take, reduced partial graft loss,
reduced rate of infection owning to a sterile environment, mitigation
of wound bed edema, and reducing hospital length of stay.
33,34
Foam
sponge should be covered with a nonadherent layer and customized
to be the size of the graft. Common settings include low, continuous
suction at 100 to 125 mm Hg negative pressure. This dressing most
often stays in place for 4 or 5 days.
The donor site should not be overlooked as this is most often the
source of the patient’s primary concerns after skin graft
reconstruction. The donor site is painful because of the exposure of
free nerve endings in the skin; this pain peaks by the third or fourth
day after surgery and then tails off thereafter.35 Additionally, the
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