Skin grafting Flashcards
A skin graft is a portion of skin that has been separated from its vascular supply
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Full-thickness grafts (epidermis and dermis plus adnexal structures) are more appropriate where a large area is to be grafted.
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This is true for split thickness grafts.
Split-thickness grafts (epidermis and partial-thickness dermis only) generally give better retention of skin function.
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This is true for FTSG.
Disadvantages of grafts include creation of a second surgical site and suboptimal tissue colour and texture match if an improper donor site is selected.
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Patients typically will eventually experience full sensation at the graft recipient site.
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Rarely, even after prolonged periods.
Split-thickness grafts contain few or no adnexal structures.
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Composite grafts consist of skin and a second type of tissue, most often cartilage.
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A homograft is a graft taken from a donor site on an individual and placed at a recipient site on that same individual.
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This is an autograft.
An autograft is a graft taken from an individual and transplanted to another individual of the same species.
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This is a homograft.
A xenograft (heterograft) is a graft that is transplanted between species (eg. pig to human).
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Re-establishment of a blood supply at the recipient site is essential for graft survival.
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Imbibition is the first stage of graft survival – it is an ischaemic period that lasts for the first 24-48 hours.
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During imbibition, the graft becomes oedematous, but does not increase its weight.
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Weight increases by up to 40%.
During imbibition, fibrin attaches the graft to its bed, the graft is sustained by plasma exudate from the wound bed, and nutrients are obtained by passive diffusion.
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Ultimately the fibrin ‘glue’ is replaced by granulation tissue.
The second stage of graft survival is neovascularisation.
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Inosculation.
The third stage of graft survival is inosculation.
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Neovascularisation
inosculation is second stage
But 2nd and 3rd stages occur concurrently
Inosculation is a process of revascularisation, resulting in the linkage of the graft’s dermal vessels to those present in the recipient bed.
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The process of inosculation begins as early as 48-72hrs and lasts for 7-10 days.
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Occurs concurrently with neovascularisation
Despite the fact that exposed bone and cartilage are poor substances for grafts, delayed grafting at sites initially devoid of periosteum or perichondrium allows for the development of granulation tissue and improved chance of subsequent graft survival
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Neovascularisation refers to capillary ingrowth to the graft from the recipient base and sidewalls.
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Neovascularisation and inosculation typically occur at separate times during healing.
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Often occur in conjunction.
The rate at which a skin graft revascularises is a function of both the fraft thickness and the recipient bed vascularity.
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Under optimal healing condition, full circulation can be restored to a graft after 2 weeks.
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Between the 4th and 7th day.
Re-establishment of lymphatic flow occurs concurrently with restoration of the blood supply and is usually completed by the end of the first week of graft healing.
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Upon return of lymphatic drainage, the graft begins to lose the weight that was acquired during imbibition and likewise begins to lose the bulkiness noted earlier in the healing process.
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Reinnervation of grafts occurs simultaneously with blood revascularisation and return of lymphatic drainage.
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Slow process – begins within 2 months, may not be complete for years (if at all).
Medical issues relevant to skin grafting include coagulation abnormalities, alcohol consumption, smoking, vascular disease, metabolic derangements, and poor nutrition.
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FTSGs generally have greater wound contracture than STSGs.
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The opposite is true.
The metabolic demands limit the overall size of a FTSG to 4-5cm, but STSGs can be used to repair very large defects.
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Sites where STSGs are commonly utilized include the nasal tip and ala, helical convexities and concavities, medial canthus, digits and extremities.
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This is true for FTSGs.
Factors contributing to donor site selection include skin colour, tissue texture, amount of photodamage, and the presence or absence of hair.
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Most common donor sites include preauricular skin, postauricular skin, clavicular and inner upper arm regions, the mesolabial fold and upper eyelids.
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Harvested grafts should be oversized by 40-50% to prevent obtaining a final graft that is too small.
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10-20%.
Defatting of the graft is performed effectively with curved iris scissors.
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Leaving fat on the graft serves as a barrier to nutrient diffusion between the recipient bed and the graft dermis.
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Remoistening the graft periodically with sterile saline or local anaesthetic during the defatting procedure is not recommended.
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Is recommended to prevent desiccation.
The graft recipient site should not be undermined.
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Undermine by several mm.
Meticulous haemostasis of the recipient site is not necessary.
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This is crucial.
Excessive elctrocoagulation of the wound bed must be avoided, so that abundant devitalised tissue is not present.
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A subcutaneous or myocutaneous hinge flap can be utilised prior to graft placement to more fully occupy the base of the recipient site with well-vascularised tissue.
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Buried sutures should not be placed to anchor the graft.
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This increases the risk of haematoma.
The optimal suturing technique is with the needle entering the graft first, which results in less ‘lifting’ tendency of the graft from its new base.
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Excessively superficial suturing on the graft onto its recipient bed has been implicated as a potential aetiology of graft pin-cushioning.
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Basting sutures should not be placed to anchor the central portion of the graft.
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These secure the central portion, protecting it from shearing forces.
Tie-over bolsters are essential for good surgical outcome
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Silk sutures are ideal for tie-over bolsters, due to their excellent knot security and handling properties.
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Tie-over sutures can be placed entirely within the surrounding recipient skin or between the simple interrupted sutures anchoring the graft.
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A bolster consists of a thick layer of antibiotic ointment or petrolatum applied over the graft, followed by a non-adherent contact layer, with a bulky material making up the final layer.
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A Burow’s graft is a FTSG in which the grafted tissue is obtained from skin not adjacent to the defect.
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Adjacent.
Grafts from the crown of the scalp are best used as donor sites on the scalp.
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Occipital and temporal – least likely to undergo AGA.
Hair-bearing grafts should be defatted using the same technique as for non-hair bearing skin.
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Should be defatted minimally or not at all in order to preserve follicles.
Orientation of hair-bearing grafts is unimportant.
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Need to orient so hairs in same direction as surrounding skin.
Thin STSGs are 0.125-0.275mm thickness.
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Medium STSGs are 0.275-0.4mm thickness.
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Thick STSGs are 0.40-0.75mm thickness.
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STSGs can be harvested with free-hand use of a #10 or #15 blade, a Weck blade or a dermatome.
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Using a free-hand blade to take a STSG has the advantage of being easy to obtain a graft with uniform thickness
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It is very difficult to obtain a graft with unform thickness
A Weck blade should be held at a 45 degree angle to the skin during harvesting.
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Virtually parallel.
Air-driven or electric dermatomes should be used when STSGs are necessary to cover larger defects that are several cms in size or greater.
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Meshing STSGs increases the coverage area by 50-60%.
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25-35%.
Donor sites for STSGs include the upper thigh, lateral hips, inner aspects of the upper arms, low back, and abdomen.
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Moist occlusion of the STSG donor site significantly decreases post-operative pain and promotes re-epithelialisation.
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The STSG donor site usually re-eptihelialises over 4-5 weeks.
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2-3 weeks.
The STSG donor site typically remains pink for several months, and later become hypopigmented
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There is significant drainage at the donor site of a STSG for the initial 24 hours
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48hrs
The maximum graft diameter for a composite graft is 1-2cm, to minimise the risk of necrosis.
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The crus of the helix is the most commonly used donor site for composite grafts.
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The reverse tongue-in-groove technique for composite grafting requires no oversizing of the graft when compared to the defect site.
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5-10% oversizing due to predictable contaction of the graft over time.
It is not necessary with composite grafting to avoid placing excessive cartilage.
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Post-operative necrotic debris should be removed from the graft bed as it signals complete graft loss.
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Often viable graft underneath so leave intact.
Delayed grafts are most commonly necessitated for defects with a significant amount of exposed bone or cartilage, where greater than 25% of the periosteum or perichondrium is lacking.
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These recipient bases often provide inadequate nutrition and grafts placed directly over them are at increased risk of necrosis.
On the day of surgery for the delayed graft the recipient site is gently scrubbed with a sterilizing agent as these wounds are likely to be colonised with bacteria despite antibiotics
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Preparation for delayed grafting involves beginning oral antibiotics one day prior to the procedure and continuing for 4 days postoperatively.
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Porcine xenografts are occlusive biological dressings that promote granulation and may remain in place for 7-14 days.
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Dermal grafts are fragments of skin from which the epidermis has been removed.
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Dermal grafts can be used as filler and contouring material in wounds on convex surfaces.
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Complications of dermal grafts occur rarely, but include epidermal cyst formation.
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Epidermal cysts occur in ~10% cases.
Dermal grafts negate the need for definitive repair with a graft or flap.
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graft on top
The biggest risk to graft survival comes from the patients themselves.
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At 1 week, FTSGs are typically violaceous in appearance.
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One of the clues that the surface of a FTSG is truly necrotic is a ‘gummy ‘ or ‘spongy’ feel with gentle pinching of the surface with toothed forceps.
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The patient can begin to treat a graft recipient site as normal skin, including the use of cosmetics, at two weeks.
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One month
STSGs are pink-to-skin coloured as early as one week.
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Re-epithelialisation of fenestrations of extensively meshed grafts can require up to 2-4 weeks.
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6-8 weeks
STSGs have a tendency to become dry, scaly and hyperkeratotic over time.
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need to use liberal emollient.
Routine antibiotics are required in the perioperative skin graft period
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The most common complication leading to loss of any graft is fluid accumulation at the graft base that elevates it from the recipient bed.
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Antibiotics should be used for delayed grafts, or in cases where to surgical wound has been open for a prolonged period (>6hrs) or for surgical sites close to the mouth or nostrils.
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Long-term complications of skin grafts include poor cosmesis and functional deficits such as ectropion and nasal valve collapse.
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FTSGs are nearly always aesthetically inferior to STSGs.
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Other way round.
The anatomic sites most likely to be susceptible to the effects of graft contracture are the eyelid, vermillion border of the lip, and nasal ala, since they have ‘free margins’
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