12.1 Introduction
Attempts to develop skin substitutes that may function as normal, healthy integument have been made for many years in the treatment of burns, surgical wounds, cutaneous ulcers, and other skin defects. The accepted term for skin substitutes originally derived from living tissues is ‘biological dressings’. This term is used regardless of whether the substitutes contain liv- ing cells or not.
The classic, simple technique of applying bi- ologic dressings is to use autologous split- thickness or full-thickness skin grafts, surgical- ly excised from the patient’s own healthy skin.
Skin grafting is known to have been used some 3000 years ago in India [1–3] and there are iso- lated reports of its use during the nineteenth century [1–3]. The first documentation of skin grafting in humans in the ‘early modern’ medi-
Skin Grafting
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Contents
12.1 Introduction 159 12.2 Split-Thickness Skin Graft
and Full-Thickness Skin Graft 160 12.3 Preparing a Cutaneous Ulcer
for Grafting 160
12.4 Forms of Autologous Grafting 161 12.5 Conclusion 162
References 163
... skin for skin and all that a man has he will give for his life.
(Job II: 4)
’’
cal literature is attributed to Reverdin in 1869 [4]. The procedure of grafting became com- monly accepted, especially for burns, following the invention of the dermatome by Padgett and Hood, reported in 1939 [5].
Grafting autologous skin is still a commonly accepted method of covering a cutaneous sur- face denuded by a variety of causes, such as cu- taneous ulcers [6–14].
Possible forms of skin grafting are as follows:
5
Autograft (or ‘autologous graft’): a graft originating from one part of the body and transplanted onto an- other area (from patient’s own healthy skin)
5
Isograft (or ‘isogeneic graft’): Iso- grafting usually relates to laboratory animals belonging to the same species and sharing an identical genetic makeup. In human beings, an isograft is any sort of graft transferred from one genetically identical twin to the other.
5
Allograft (or ‘allogeneic graft’; previ- ously termed ‘homograft’): a graft from one person to another, who do not have identical genetic character- istics; in general, it is transferred from one individual to another of the same species
5
Xenograft (syn. ‘heterograft’): a graft taken from an individual of one spe- cies and transplanted onto an indi- vidual of another species. (The term
zoograft has a similar meaning andrefers to a graft from an animal to a human.)
t
It follows that the most common type of skin grafts today are autografts. These will be dealt with in this chapter. The use of allografting is becoming more and more common, both in the form of allogeneic keratinocyte grafting and as composite grafting. That topic will be covered in Chap. 13. There is also use of xenografts, i.e., skin grafts from an animal – commonly a pig – which may have some use as a temporary bio- logic dressing, to be applied to extensively de- nuded areas, such as in large burn wounds.
12.2 Split-Thickness Skin Graft and Full-Thickness Skin Graft
The graft may be in the form of a split-thick- ness skin graft or a full-thickness skin graft. A split-thickness skin graft contains epidermis and a certain amount of dermis, while a full- thickness skin graft contains epidermis and the whole dermis (Figs. 12.1, 12.2)
A full-thickness skin graft offers better pro- tection from trauma. It does not contract as much as a split-thickness skin graft and gener- ally looks more natural after healing; thus, it is often used for aesthetic reasons. However, a full-thickness graft requires a well-vascular- ized recipient bed. Because of this limitation, it is not commonly used in cutaneous ulcers. On the other hand, a split-thickness skin graft re- sults in a better ‘take’, even when applied to tis-
sue in which vascularization is not optimal and relatively reduced (Fig. 12.3). This feature makes it more appropriate for use in the management of cutaneous ulcers.
The thicker the graft, the smaller the extent of contraction of the grafted wound. Similarly, wounds covered with thin split-thickness skin grafts contract less than open wounds [15].
12.3 Preparing a Cutaneous Ulcer for Grafting
Grafting should be done only onto a viable wound surface. Prior to the application of the skin graft, the ulcer bed should be debrided to remove any necrotic tissue. Vital granulating tissue should be exposed, thereby enabling cells
Chapter 12 Skin Grafting 160
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Fig. 12.1.Histological representation of a full-thickness skin graft
Fig. 12.2.Histological representation of a split-thickness skin graft
Fig. 12.3.A split-thickness graft is placed on a cutaneous ulcer. Longitudinal incisions in the graft were made in order to facilitate drainage of secretions and prevent their accumulation under the graft, which would pre- vent its ‘taking’
in the graft to attach to the ulcer’s surface and its blood supply. Note that the presence of more than 10
5bacteria per gram of tissue should be regarded as infection (see Chap. 10).
12.4 Forms of Autologous Grafting
A simple autograft, applied as a layer, whether done with a dermatome, a scalpel, or a special grafting knife, may provide appropriate biolog- ical coverage. However, it must be remembered that the harvesting of an autograft results in a wound in the healthy donor skin, analogous to a second-degree burn. The donor wound, apart from being painful, may require a considerable amount of effort and time to heal. Therefore, several techniques have been developed to re- duce the required surface area of the donor skin.
Techniques in use for applying autologous grafts are:
5
Taking one sheet of grafted skin to cover all the denuded area: A split- thickness graft is harvested with a dermatome; a full-thickness graft is usually obtained using a small scal-
5pel. Small pieces: One way of decreasing the required area of donor skin is to apply smaller pieces of donor skin, instead of one large sheet that cov- ers the entire area of the ulcer.
These grafts are placed onto the ul- cer bed at regular intervals, to allow drainage of secretions.
5
Pinch grafting was documented as early as 1869 by Reverdin [4, 16].
The skin is anesthetized, a small portion is lifted up on the point of a needle, and the top is cut off with a scalpel. Pinch grafts should be of full thickness, 3–5 mm in diameter.
The grafts are evenly placed on the ulcer bed, with free spaces of 5 to 10 mm between each of the grafts.
Pinch grafting has been document- ed several times in the past 20 years
as a possible treatment method for chronic skin ulcers [17–23].
5
Punch grafts, obtained by using a punch biopsy instrument, represent another modification of full-thick- ness autografting. This procedure enables a smaller area of donor skin to be used, assuming that epithelial- ization will take place and advance peripherally from each punch. The punch method is still used [24]. The punch grafts, which may be 3–5 mm in diameter, are placed onto the ulcer’s surface at regular intervals.
5
Mesh grafting (Fig. 12.4): A mechan- ical device is used to cut multiple slits in the graft, thereby allowing it to be stretched, so that it can ex- pand and cover a larger surface ar- ea. This procedure is commonly used for burns, where large areas of donor grafts may be needed, but not for cutaneous ulcers.
Ahnlide and Bjellerup [17] used pinch grafting for 145 therapy-resistant leg ulcers. Three months following the procedure, the average healing rate was 36%. Poskitt et al. [23] present- ed a randomized trial comparing autologous pinch grafting (25 patients) with porcine der-
t
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Fig. 12.4.Mesh grafting
mis dressings (28 patients). Sixty-four percent (64%) of ulcers treated by autologous pinch grafting were healed at six weeks and 74% by 12 weeks, compared with ulcers treated by porcine dermis, where healing rates were 29% and 46%, respectively, after 6 and 12 weeks.
While pinch grafting and punch grafting are usually intended for relatively small ulcers, some suggest that mesh grafting may be used for larger ulcers. Kirsner et al. [9] documented 29 patients with 36 leg ulcers of various etiology, treated by meshed split-thickness skin grafts.
The grafts were harvested with a Padget derma- tome and expanded through meshing to one and a half times their original size. The initial ‘- take’ of the grafts was recorded as ‘excellent’. At a mean follow-up of 11 months (three months to three years) 52% of ulcers were healed.
The information above covers simple auto- grafts. More advanced forms such as cultured keratinocyte grafting and tissue engineering are discussed in Chap. 13.
12.5 Conclusion
In a comprehensive Cochrane review, Jones and Nelson [6] suggest that further research is need- ed to compare the beneficial effects of ‘simple’
skin grafting with those of other modes of treat- ment intended for venous leg ulcers. This con- clusion may actually be implemented for other types of cutaneous ulcers as well.
The ‘take’ of the graft and the final result de- pend on the ulcer’s condition in terms of vascu- larization, absence of infection, and appropri- ate preparation of the ulcer bed, as well as on the patient’s general condition.
In our experience, a skin graft may provide suitable coverage for a cutaneous ulcer, result- ing in healing. However, in some cases, the graft does not ‘take’ well for the same reasons that re- sulted in the ulceration in the first place (e.g., poor vascularization) and the ulcer does not heal. Moreover, even in cases where closure of a cutaneous ulcer is achieved by skin grafting, the final clinical result is not satisfactory – in most cases because there is no adequate prolife- ration of granulation tissue (Fig. 12.5). The orig- inal ulcer site usually remains as a depression
in the skin, with inadequate subcutaneous tis- sue covered by a thin, very vulnerable cutane- ous layer. Hence, autologous skin grafting of cutaneous ulcers is commonly followed by re- ulceration.
In view of the above, advanced modalities such as keratinocyte grafting, composite grafts, or preparations containing growth factors, which may stimulate proliferation of granula- tion tissue, may be used (see Chaps. 13, 14, and 15). The use of advanced modalities (e.g., growth factors) may indeed result in complete healing of a treated ulcer, even without skin grafting. However, in many cases this stimulus will not suffice for healing and closure – espe- cially with relatively large chronic ulcers. It may well be that the solution to the problem of cer- tain ulcers will lie in a combination of such ad- vanced modalities together with skin grafting.
Chapter 12 Skin Grafting 162
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Fig. 12.5.Cutaneous ulcers following grafting and par- tial (b) and complete (a) healing. Note that the area is slightly depressed due to decreased production of gran- ulation tissue during active stages of healing
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