Concepts of Skin Grafts and Skin Substitutes Flashcards
Split-thickness skingrafts, whencompared with full-thickness
skin grafts may experience more pigment changes,
be more susceptible to trauma, and have a lower metabolic
demand of the recipient site wound bed
T
Skin grafts heal by a process of imbibition and revascularization through angiogenesis.
T
eventual reepithelialization over a
span of about 8 weeks.
F 4 WEEK
15% of total
adult body weigh is skin
T
the dominant cell
type in the dermis dendrocytes
and mast cells
F fibroblasts are the dominant cell
type in the dermis
the pilosebaceous units and sweat glands present in papilary derms
F reticular dermis
secondary contraction is a myofibroblast-mediated process
T
both
split-thickness and full-thickness grafts are vulnerable to shear forces
during the healing process
T
grafts with less dermal
element are less fragile to subsequent trauma
F grafts with a larger dermal
element are less fragile to subsequent trauma
Thicker skin
grafts place greater metabolic demands on the wound bed during
healing
T
split-thickness skin grafts
also generally do not contain intact accessory skin structures such as
hair follicles and sweat glands.
T
Skin graft take has historically been broken down into three
classic phases
imbibition (0-48 hours)
inosculation (48-72 hours)
revascularization (>96 hours)
graft survival has been shown
to be dependent on the vascularity of the recipient site site
F graft survival has been shown
to be dependent on the vascularity of the donor site (with grafts harvested from a highly vascular area healing better than a graft from a
poorly perfused area
Freshly harvested grafts have also been shown
to attract blood vessel ingrowth more rapidly than grafts that have
been frozen and subsequently thawed
T
Freshly harvested grafts less tolerant
of the ischemic period because of increased metabolic activity
T
The first stage of skin graft healing is an ischemic phase known as plasmatic or serum imbibition
T
lmbibition it is alaways last for 28 hours
F tlasts approximately 24 hours in a proliferative wound
48 hours in a fresh wound
several days in a poorly perfused wound bed
As the
grafts absorb serum, they become edematous and gain as much as
40% of their initial weight in the first 28 hours
F in the first 24 hours
starting to decrease
in weight after 24hours
F starting to decrease
in weight after 96 hours
During imbibition, metabolism within the graft becomes anaerobic
T
inosculation phase is no longer vaible idea
T
connections between the wound bed vessels and graft vasculature do
occur with angiogenesis and new vessel
ingrowth in a unidirectional fashion from the wound bed into the
graft
T
new vascular connections do not necessarily
occur at the wound interface with the graft
T
A peak in vessel density is seen at
postgraft day 7
T
With the vascular density at the interface increasing
2.5-fold between post-graft days 3 and 7 before returning to levels near
those of post-graft day 3 by day 10.
T
After 96 hours, both the wound
bed and the skin graft demonstratedincreased capillary diameter and
functional capillary density
T
By 10 days after grafting (240 hours), the skin graft was fully
revascularized,
T
At 120 hours(5 days), capillary diameter and functional capillary density
within the wound bed began to decrease, while still increasing within
the graft
T
angiogenesis is the primary factor in skin graft revascularization, beginning as early
as 24 hours after grafting
T
native microcirculation start within the graft in 48 to 72 hours
T
graft vessels demonstrate an angiogenic response to
reperfusion between 3 and 8 days post grafting
T
Matrix metalloproteinases MTl-MMP and MMP-2 are associated
with the initiation of angiogenesis
T
Preexisting vascular
channels in the periphery of the skin graft were 100% replaced by
vessel ingrowth from the wound bed by day 10, whereas those in the
center ofthe graft were replaced to a much lesser extent (50%-60%)
T
During the first 10 days after grafting, the epidermis of the graft doubles in thickness
F During the first 4 days after grafting, the epidermis of the graft doubles in thickness
This increased cellular turnover
does not return to baseline until 2weeks after grafting
F 4 week
It is generally
accepted that fibroblasts within the dermis ofa healing skin graft are
not native graft fibroblasts
T
Collagen turnover in the
the dermis, peaking at 2 to 3 weeks after grafting at three to four times faster than the collagen turnover rate for normal skin
T
Approximately, 85% ofthe original collagen in a skin graft is replaced within 5 months of grafting
T
split-thickness grafts replace mor than their original collagen compared with full-thickness grafts ofthe same size
F split-thickness grafts replace only half as much of their original collagen compared with full-thickness grafts ofthe same size
Elastin
within the graft is also replaced, with degeneration from postgraft day 3,
and regeneration starting 4 to 6 weeks after grafting.
T
A full-thickness graft loses approximately 40% of its surface area after harvest whereas a split-thickness graft loses
10% to 20% ofits area
T
Secondary contraction is increase with increasing the amount of dermis in the graft
F inversely proportional to the amount of dermis in the graft
Graft with collagen
matrix, in fact behaves much like full-thickness skin grafts in terms
of inhibiting wound contraction
T
Once wound contraction is complete, full-thickness grafts &split thickness graft are able to grow with the surrounding tissue,
F Once wound contraction is complete, full-thickness grafts are able to grow with the surrounding tissue, whereas split-thickness grafts remain fixed
skin
grafts take approximately 2 weeks longer to heal in diabetic patients
than in nondiabetic patients
T
Gauze
dressings had the highest infection rates
T
Time to complete reepithelialization was 7 days (30%) shorter when hydrocolloid
dressings were used
T
it is generally accepted
that the dressing should maintain a moist wound environment for
at least 3 days
F it is generally accepted
that the dressing should maintain a moist wound environment for
at least 1 week.
cultured autografts and cultured allografts epidermal grafts can be used
T
Epicel is……
cultured epidermal autografts
Limitation of use Epicel
variable graft take rate, limited mechanical resistance, hyperkeratosis, scar
contracture, ulceration, and blister formation because of reactions
to foreign fibroblasts in feeder media, as well as the lengthy culture
time (3-4 weeks) required and the high cost
keratinocyte activation, growth factor secretion, and reepithelialization from the wound edge, more akin to cultured keratinocytes than
full- or split-thickness grafts
T
Dermal-epidermal grafting llows expansion by a factor of 1:100 (instead of the typical
1:5 expansion of a full-thickness skin graft and 1:9 expansion of a
meshed split-thickness skin graft)
T
Micrografts need to
retain their dermal orientation,
F Micrografts also do not need to
retain their dermal orientation,
Micro grafting take place
under local anesthetic in an outpatient setting
T
Fractional skin harvesting is done by harvesting split-thickness skin tissue
F Full thickness skin tissue
The high
antigenicity of skin allografts, in particular, the epidermal layer
T
Dermagraft IS …..
is created by seeding neonatal foreskin fibroblasts onto a biodegradable polyglycolic acid mesh
In integra New blood vessels can be seen in the deep portion of the matrix by
day 12 and reach the superficial surface by day 28
T
Wen we can put skin graft after the integra?
After1 week
Integra can also be used without the silicone layer as a
filler for contour deformities
T
Integra without the silicone layer can lead to from eccessive granulation tissue
T
myofibroblasts start migrating into the matrix and start producing collagen by the beginning of week 3. The silicone epidermal
layer has usually sloughed or been removed by this point in time with integra
T
Integra can also be used without the silicone layer as a
filler for contour deformities, although this does require a lengthier
period of neovascularization for vessel ingrowth through a thicker
matrix
T
use of this
product, especially in combination with other modalities such as negative-pressure wound therapy, can often generate granulation tissue
even over challenging surfaces, such as bone, tendon, and hardware
T
