Chapter 26 - Skin Grafting Flashcards
What is the main reason for sking grafting?
The most common indication for applying a skin graft to a horse
is a wound so large that it cannot heal by any other means
A healed sking graft contains how many skin layers?
3 epidermis, dermis and adnexa including hair follicles
two basic types of skin grafts are the
pedicle graft and the
free graft
Definition of pedicle graft
pedicle graft remains connected to the donor site,
at least temporarily, by a vascular pedicle that sustains the graft,
ensuring its viability
pedicle graft is useful for covering a ___________ ___________ (2w) wound
poorly vascularized wound because the graft is not dependent
on the vascularity of the recipient site
cosmetic appearance
of wounds healed by applying a pedicle graft is
good
what is the name of the artery and veiin responsible for vascularization of flaps
direct cutaneous artery and vein
free skin graft is a piece of skin that
has been completely
separated from its local blood supply and transferred to a wound
at another site, where it must establish new vascular connections
to survive
Free grafts can be categorized in several different
ways, one of which is by their source. Name them
autograft (or isograft)
allograft (or homograft)
xenograft (or heterograft).
Free skin grafts can also be categorized according to their thickness. Name them
Full-thickness grafts
split-thickness (or partial-thickness) grafts
Definition of split-thickness (or partial-thickness) grafts
composed of epidermis and only a portion of the dermis
Definition Full-thickness grafts
composed of epidermis and the entire dermis
The percentage of dermis within the graft influences the
acceptance, durability, and cosmesis at the recipient site.
The thickness of dermis within the graft is directly proportional to the graft’s (name 2 factors)
durability
cosmesis
The thickness of dermis within the graft is indirectly proportional
to the graft’s ability to survive
Full- or split-thickness free skin grafts can be applied to the surface of wounds as:
1- solid
2- or meshed sheets,
or they can be embedded in granulation tissue
3- as pinch,
4- punch,
5- or tunnel grafts.
free graft cannot be expected to survive if placed on (3 structures)
1) on bone denuded of periosteum,
2) tendon denuded of paratenon,
3) or cartilage denuded of perichondrium,
Figure 26-2. Proliferating epithelium at the margin of a wound on the hip of a horse. Proliferating epithelium, represented by the pale ring around the edge of the wound, indicates that the wound is healthy enough to accept a skin graft.
A prime requisite for free grafting is a recipient bed that is (3 characteristics)
vascular
and
free of infection
and devitalized tissue.
Graft is initially adhered to the recipient site by
fibrin
Vessels and fibroblasts invade the fibrin matrix by
4th or 5th day and the graft is firmly united to the recipient bed by around the 10th day
newly applied graft is nourished by
plasma-like fluid
A thin skin graft is better/worse (choose 1 option) nourished during this phase of acceptance
better, because the quantity of nutrients able to permeate the graft is inversely proportional to the thickness of the graft.
new capillaries generated in the recipient bed traverse the fibrin layer to anastomose with those in the graft, a process called
inoculation
Organization (Organic Union) - epidermis of the graft becomes hyperplastic after grafting and can double in thickness during the first
2 weeks
Who has a more interrupted vascular area full-thickness or partial/split thcinkess?
full-thickness graft is less interrupted than that within the dermis of a
split-thickness graft
Dermis can be differentiated from granulation tissue by its ______________ color (1w)
paler color
Split-thickness grafts of horses, no matter the thickness at which the grafts are harvested, are likely to be devoid of ____________________(2w)
sebaceous glands
Hair begins to appear in split-thickness grafts at between ___ and ____ weeks
Hair begins to appear in split-thickness grafts at between 4 and 6 weeks
The growth of longer hairs may be related to a difference in _____________________ (1w) between the grafted limb and the donor site.
The growth of longer hairs may be related to a difference in temperature between the grafted limb and the donor site.
Reinnervation returns more rapidly, in split-thickness grafts or in full-thickness grafts?
Reinnervation returns more rapidly, but to a lesser extent, in split-thickness grafts than in full-thickness grafts
Split-thickness skin grafts of horses usually begin to develop pigment about _____weeks after grafting
Split-thickness skin grafts of horses usually begin to develop pigment about 4 weeks after grafting
After being harvested, grafts immediately shrink – referred to as
primary contraction
Primary contraction is greatest in full thcinkess grafts or decreased grafts?
Primary contraction is greatest in full-thickness grafts and decreases as grafts become thinner.
Full-thickness grafts from humans contract to nearly
half their original size after being harvested.
Split-thickness grafts that are about half the thickness of the whole skin contract to about
three quarters of their original size, and grafts composed solely of epidermis do not shrink at all.
Skin grafts inhibit wound contraction, to various extents, by accelerating the life cycle of the ___________(1w) within the wound.
myofibroblasts within the wound
Full thickness graftss tend to contract less or more than wounds receiving a split thickness graft?
Contract less in full thickness
contraction of wounds of horses, before or after grafting, should be considered beneficial
yes because it results in more rapid healing and smaller scars
A hematoma, a seroma, or exudate beneath the graft prevents ________(1w) from attaching the graft to the wound and acts as a barrier to the ingrowth of new vessels
A hematoma, a seroma, or exudate beneath the graft prevents fibrin from attaching the graft to the wound and acts as a barrier to the ingrowth of new vessels
graft can survive for only several _______ by imbibing nutrients from the hematoma or seroma
graft can survive for only several days by imbibing nutrients from the hematoma or seroma
Ideally, a hemorrhagic wound should not be grafted until hemorrhage has ceased - TRUE or FALSE
TRUE
Wgat is the concentration that seem to infect the tissue and exceed the ability of humoral and cellular defenses?
by quantitative bacterial analysis, to contain more than 105 bacteria per gram of tissue
Quantifying the concentration of bacteria in a wound is time-consuming and often impractical - what is very important to know?
Type of bacteria - most notably β-hemolytic streptococci and Pseudomonas spp., required to infect a wound is much less than 105 per gram of tis
most notably β-hemolytic streptococci and Pseudomonas spp., produce which type of proteolytic enzymes?
streptokinase and staphylokinase
What does the streptokynase and staphylokinase do?
they destabilize the fibrin network between the graft and the recipient wound by catalyzing the conversion of plasminogen to plasmin, which digests fibrin
Sprouting capillaries capable of rapidly revascularizing the graft develop in the wound within
48 hours
Factors to take in consideration when determining if the wound is prepared to receive a graft
wound vascularity
potential wound infection
Hgihgly vascular granulation tissue readily accepts a graft, but as the granulation tissue matures its vascularity and ability to accept a graft ___________(1)
diminish
Wounds allowed several days to develop sprouting capillaries before being grafted are referred to as
“prepared wound”
Removing streptococci from wound is relatively eay because they are susceptible to
penicillin
Occasionally, penicillin or other β-lactam antibiotics are ineffective in resolving a streptococcal infection, because other resident bacteria, particularly __________ and ________________ produce β-lactamase, an enzyme that inactivates β-lactam antibiotics.
Occasionally, penicillin or other β-lactam antibiotics are ineffective in resolving a streptococcal infection, because other resident bacteria, particularly staphylococci and gram-negative bacteria, produce β-lactamase, an enzyme that inactivates β-lactam antibiotics
Topical application of an antimicrobial drug to an infected, granulating wound is more effective for eliminating infection than is systemic administration of the same antimicrobial drug - TRUE or FALSE
TRUE
Granulation tissue within chronic, slowly healing wounds, particularly those wounds that appear to be pruritic, should be examined histologically for the presence of
larvae of the equine stomach worm Habronema
Which type of neoplasms resemble granulation tissue?
sarcoids or carcinomas
Figure 26-5. Burn wound on the back of a horse. (A) The wound contained exuberant, relatively avascular granulation tissue that was excised to skin level, with the horse standing, in preparation for grafting. (B) About 75% of a meshed, split-thickness skin graft, applied several days later, was accepted.
Pseudomonas spp. are usually sensitive to topically applied ___________, ____________ and______________(3w)
mafenide acetate, aminoglycosides, or polymyxin-B sulfate
Figure 26-6. A graft applied to a healthy-appearing, granulating wound on the dorsal aspect of a metacarpus was completely accepted, but a draining tract soon appeared in the healed wound (left). Drainage was caused by infection of bone beneath the wound and the development of a bone sequestrum (right).
How to prepare the recipient bed immediately before grafting? 4 steps
Remove hair form the skin surrounding the wound
Surgical scrub solution to cleanse the skin around the wound
Wound itself should be cleansed only by rinsing with physiologic salin
The graft should be cut slightly larger/smaller (choose) than the recipient sit
larger
Because subcutaneous tissue attached to the undersurface of the graft acts as a barrier to _____________________(2 w) and ________(1w) of new vessels, it must be removed to expose the dermis and its vasculature
Because subcutaneous tissue attached to the undersurface of the graft acts as a barrier to plasmatic imbibition and ingrowth of new vessels, it must be removed to expose the dermis and its vasculature
Figure 26-10. The Watson skin-grafting knife. Using this dermatome, a surgeon can harvest a graft 100 mm (4 in) wide. The knife uses disposable blades and is fitted with an adjustable roller in front of the blade to control the depth of the cut.
Which free graft provides the best cosmetic appearance?
full-thickness skin grafts
Full thickness grafts are not accepted as readily split thickness grafts, why? 2 reasons
because they have:
- fewer exposed blood vessels than do split-thickness grafts
- because their requirement for nourishment is greater
Figure 26-15. A Zimmer mechanical skin mesher. The mesher is capable of expanding the graft to many times its original area. The graft is positioned on a specially grooved plastic carrier, and the graft and carrier are fed through the mesh cutter by turning a hand crank.
Figure 26-14. A Padgett mechanical skin mesher. The mesher consists of an aluminum block with staggered, parallel rows of blades and a Teflon rolling pin. The graft is positioned on the block, dermal side down, and pressed into the cutting blades with the rolling pin.
Figure 26-13. Harvesting split-thickness skin from the ventral aspect of the abdomen using a free-hand knife. The ventral portion of the abdomen must protrude over the edge of the table to accommodate the handle of the hand-held knife. Slight, uniform tension is applied to the cut end of the graft as the graft is harvested.
Figure 26-11. Harvesting a skin graft with a drum dermatome. (A) Rotating the drum of a drum dermatome elevates skin to which it has been glued. (B) The skin attached to the drum is cut at a precise depth with a knife that oscillates back and forth on a piston.
Figure 26-12. Harvesting a split-thickness skin graft with a pneumatic dermatome. Although they are expensive, power-driven dermatomes allow the cutting of very uniform grafts by minimally experienced operators.
A split-thickness graft is composed of 2 portions name them
Epidermis and a portion of dermis
To obtain a split-thickness graft, a portion of the dermis and its overlying epidermis is harvested with a
Free hand knife
drum dermatome
power-driven dermatome
Donor sites for obtaining a split-thickness graft
ventral portion of the abdomen
ventrolateral aspect of the thorax, caudal to the elbow
How does the adjustable roller of the Watson knife affect the harvest of skin grafts?
It controls the depth of the cut, allowing for moderate practice to achieve uniform graft thickness.
What factors influence the thickness of the harvested skin graft?
The position of the roller, angle of incidence, and pressure applied during cutting.
What is the operational mechanism of a drum dermatome?
It uses an oscillating knife on a piston to split the dermis while the skin is glued to the rotating drum.
How does a drum dermatome allow for precise graft harvesting?
The depth of the cut is predetermined by the caliber of shims placed next to the blade.
What is a significant limitation of the drum dermatome when harvesting grafts for horses?
The length of the graft is limited by the circumference of the drum.
What types of power-driven dermatomes are commonly used?
The Stryker electric dermatome and the Brown pneumatic or electric dermatome.
What comparative advantage does a pneumatic dermatome have over an electric one?
The cutting head of a pneumatic dermatome oscillates more rapidly, leading to smoother harvesting.
Why might grafts obtained with the Davol-Simon dermatome be insufficient for horse wounds?
They are too thin (0.38 mm) to provide an adequate cosmetic appearance
What is a key advantage of using a free-hand knife over power-driven dermatomes?
It allows harvesting of consistently uniform grafts wider than 100 mm and is generally less expensive.
What preparation must be done before using a free-hand knife to harvest skin from a horse?
The horse should be anesthetized, and the abdomen positioned properly over the edge of the surgery table.
How can the operator’s hand position affect graft harvesting using a free-hand knife?
A right-handed operator finds it easier when the horse is in right lateral recumbency and vice versa for left-handed operators.
What technique helps to reduce friction during the use of a free-hand knife?
Lubricating the donor site with saline and the blade with mineral oil.
Figure 26-30. A Meek micrograft machine shown with a hand-drive (a machine with a pneumatic motor for turning the knives is also available). The cutting block with the cork template and graft are passed through the Meek micrograft machine, which contains 13 circular knives that
cut the graft into 14 strips of 3 mm width. The cork holder is rotated 90 degrees and replaced onto the cutting block, and by passing it through the machine again, the strips of graft are cut into 196 (14 × 14) micrografts of 3 × 3 mm size.
Figure 26-33. (A) A nonhealing wound on the palmar aspect of a metatarsus is almost healed after receiving Meek micrografts 24 days earlier. The original square Meek micrografts from which epithelialization proceeds can still be seen. Only tiny areas remain to be epithelialized. (B) Five months after grafting, the grafted site is covered with hair the same color as that at the donor site. The hair coat is somewhat sparser than the surroundings because the newly formed epithelium between the micrografts does not produce hair
Figure 26-34. The donor site of a split-thickness graft 2 weeks after the graft was harvested. The donor site is nearly covered by epithelium. The new, pink epithelium will begin to develop pigment within a month, causing the epithelial scar to become black.
Figure 26-35. A recently applied graft destroyed by streptococcal infection.
