Skin is the primary protective barrier of the body against external mechanical, chemical or biological threats. Raw areas created on the skin surface by a variety of causes exposes the body to the harmful effects of these threats. Thus it is important to make good any loss of skin or mucosal surface lost by burns, surgical procedures or other injuries.
In managing the defects both of skin and mucous membrane which follow excision of lesions, closure by direct suturing is used when the defect is small enough and is otherwise suitable. Likewise, small defects produced by burns or ulcerations are allowed to epithelise primarily. When the defect is too large, the potential methods of reconstruction are the use of a free skin graft, a local or distant skin flap, a composite flap or a free flap.
Skin grafting is the method commonly used to close superficial defects of skin and mucous membrane. Its main advantages are the technical ease of the procedure and the minimal donor site morbidity. During its transfer from donor to recipient site, a free skin graft is completely, even if only temporarily, detached from the body. While being so detached, such a graft remains viable for a limited period whose precise limit depends on the ambient temperature at which the graft is maintained. In order to survive permanently, it has to become re-attached, and obtain a fresh blood supply from its new habitat. The processes that result in its re-attachment and revascularisation are collectively referred to as ‘take’.
Anatomy of the human skin
The skin is a two-layered organ which forms the protective covering of the body. The outer layer is the epidermis, an avascular cellular structure, and the deeper layer is the dermis, which is essentially a meshwork of collagen and elastic fibres. The two are separated by a lamina, the basement membrane. Downward prolongations of the epithelium penetrate the dermis in the form of eccrine sweat glands and pilosebaceous units like apocrine glands. These specialised structures are collectively called the adnexa. The dermis is also penetrated from below by a network of blood vessels, lymphatics and nerves.
The epidermis has two main elements – the epithelial cells and the pigment system
The epithelial cells
The epithelial cells take the form of stratified squamous epithelium in which the cells, as they mature, move from the deepest layer, the basal layer, towards the surface. In the process of this, the cells become keratinised and flattened until at the surface, they finally desquamate. The thickness of the epidermis varies greatly in different body area, the thickest in the pressure zones and the thinnest in the eyelids.
The differences in the histologic appearance of different layers of the epidermis is caused by the progressive keratinisation of the cells. The structure of the cells alter as they move towards the surface, the nuclei being lost as the cells become part of the keratin layer. This regular orderly progression to maturation which takes place in normal skin from the basal layer of cuboidal shaped cells abutting on the dermis, to the final keratin layer of flattened cells on the surface, is called ‘orthokeratinisation’. The units of the cell line maturing in this way are termed ‘epidermal keratinocytes’, regardless of its stage in the maturation process.
The pigment system
The cells responsible for the production of pigment in the epidermis are the ‘melanocytes’. They are derived from the neural crest ectoderm, from where they migrate early in the foetal life to the epidermis. In the epidermis, they lie among the cells of the basal layer and the cells of the hair bulbs.
The melanocytes are triangular in section with numerous dentritic processes which run between the cells of the basal and supra-basal layers. The pigment which they produce (melanin) is synthesised as granules (melanosomes) in their cytoplasm. According to Wolff (1973), the granules move outwards along the dentritic processes from where they are transferred by phagocytosis into the adjacent keratinocytes. In these cells, the granules cluster together as a pigmented cap over the nucleus. An ‘epidermal melanin unit’ is formed by the melanocyte and the adjoining specific number (between 20 and 36) of keratinocytes subserved for it.
The melanin cuts down the transmission of ultraviolet light through the epidermis, thus reducing its damaging effect. Coloured skin has the same ratio of melanocytes to basal cells as white skin. Its darker colour is due to a greater amount of pigment concentrated in the keratinocytes.
The structural basis of the dermis is provided by the interweaving network of collagen and elastic fibres. Its upper surface is irregular, with upward projections called dermal papillae which fit into corresponding irregularities made by rete ridge pattern on the deep surface of the epidermis.
The superficial layer, the papillary dermis has a fine, loose structure and contains fine collagen, elastic and reticular fibres which run vertical to the surface, supporting the capillary loops, lymphatics and terminal nerve fibres. The deeper layer is called reticular dermis in which the collagen network is coarser in structure and runs parallel to the surface of the skin. Its deep surface has a pattern of indentations into which the fat of the superficial fascia extends to surround the secretory coils of the sweat glands.
The basement membrane
This term refers to the lamina between the epidermis and dermis, though it is doubtful if it acts strictly as a membrane. It is not of much significance in skin grafting, as even the thinnest of split-skin grafts contain at least some amount of dermis.
This is the collective term applied to the specialised epithelial prolongations which pass from the epidermis deep into the dermis. They include the pilosebaceous units and the sweat gland apparatus.
The epithelial cells of the adnexal structures constitute a biological cell line distinct from the cells of the epidermis, called adnexal keratinocytes. The distinction is more by means of biological behaviour than histological. One example is their different reaction to solar radiation. Compared with epidermal keratinocytes, the adnexal keratinocytes are relatively resistant to the effects of such radiation. Notwithstanding the differences, there exists a congruence in the basic potential of these cells. Given an adequate stimulus like the loss of surface epithelium from burning or the cutting of a split-skin graft, the adnexal cells are capable of ‘dedifferentiating’ and reverting to their ‘original’ function, of becoming epidermal keratinocytes to resurface on the skin.
The pilosebaceous unit
The pilosebaceous unit is a complex structure incorporating the hair follicle and sebaceous gland. The hair follicle extends into the dermis to varying depths, even reaching the subcutis in the scalp, beard area, upper lip and eyebrows. Towards its deepest part, it expands to form the hair bulb. The hair is formed in the hair bulb, and grows upward through the epidermis to the surface. The hair is surrounded along its length by a multi-layered sheath of follicular adnexal keratinocytes.
The sebaceous gland buds off from the side of the hair follicle. This has a lobulated structure and opens via a duct into the upper part of the follicle. The sebaceous glands are particularly numerous in the nasal skin and the naso-labial fold, and their prominence and activity in different sites vary greatly in different individuals. In the oral mucosa, they open directly into the mucosal surface. Similar direct openings of the glands into the surface is also seen in the tarsal plates of upper and lower eyelids.
The sweat gland apparatus
The eccrine glands are widely distributed over the entire skin, excluding some particular sites like the red margin of the lips. Structurally, each of these consists of a simple tube which passes downward from the skin surface deep into the dermis and ends in a coil. In some of the glands, the coil reaches a sufficient depth to lie in one of the projections of fat which extends up from the superficial fascia. More than half of the coiled element is secretory; the remainder forms part of the duct element. From the secretory portion, the duct initially continues as part of the coil, but later emerges from it to pursue a gently undulating course up through dermis until it reaches the epidermis. It spirals through the epidermis to reach the surface.
Indications for skin grafting
The common indications for skin grafting include
Large raw surfaces on skin /mucous membrane after excision of benign or malignant lesions.
- Gross loss of skin caused by burns and crush injuries.
- Non-malignant ulcers or granulating areas (e. g. diabetic ulcers and pressure sores), which have failed to epithelise after routine conservative treatment
- Raw skin /mucous membrane surfaces left at the flap donor site, not amenable to direct suturing.
- Raw mucous membrane surfaces produced by pre-prosthetic surgical procedures like vestibuloplasty.
- Raw bony surfaces produced by maxillectomy, eyeball exenteration, and excision of palatal lesions.
- Interpositional material in the treatment of temporomandibular joint ankylosis.
Types of skin grafts
The free skin grafts consist of the entire thickness of the epidermis and a variable amount of dermis. They are designated according to their dermal component as
- Full-thickness skin grafts, consisting of epidermis and the entire thickness of the dermis, and
- Split-skin grafts, containing epidermis and a variable proportion of the dermis. According to the relative thickness of dermis included, the split-skin grafts are further subdivided into thin, intermediate and thick grafts.
These various categories of grafts are not completely distinct from each other. They merely represent convenient reference points on a continuous scale of decreasing thickness from the full-thickness skin graft to the graft containing little more than epidermis. The real difference in practice is between the full-thickness skin graft and the split-skin graft.
The full-thickness skin graft, once cut, leaves behind no epidermal elements in the donor area from where resurfacing can take place; the split-skin graft leaves adnexal remnants, pilosebaceous follicles and/or sweat gland apparatus as foci from which the donor site can resurface. As a result, the donor site of the split skin graft heals spontaneously, and requires no care other than that usually accorded to any raw surface; the donor site of a full-thickness skin graft has to be closed by direct suture or, if it is too large for this, covered with a split-skin graft. This limits the size of the full-thickness skin graft which can usually be cut in practice. Extensive defects are split-skin grafted; the full-thickness skin graft is restricted to small defects.
The full-thickness skin graft takes less readily than the split skin-graft, and before it can be used, conditions have to be optimal. The full-thickness skin graft remains virtually at its original size; the split-skin graft tends to contract subsequently of circumstances permit, e.g. across a flexure. Within broad limits, the thinner the graft, the more it contracts secondarily. The stability of the graft depends on dermis, and the thicker graft stands late trauma better than the thin graft.
History of skin grafts in oral cavity
Moscovitz in 1916 treated sulcal scarring by the use of skin grafts placed over a mould which was inserted through a submental approach. 10 days later, an intra-oral incision opened the graft pocket into the mouth. Weiser (1918) and Pickerill (1919) used the intra-oral route for placing skin grafts. Gillies and Waldon (1920) and Kilner and Jackson (1921) sued he same technique for correction of post-traumatic scarring and pre-prosthetic problems. Pichler (1931) used grafts in maxillectomy operations to prevent cavity shrinkage and promote early healing.
Schuchardt (1952) suggested suturing the mucosal edge to periosteum and grafting only the periosteal surface to overcome the problems created by the soft tissue-based graft. Obwegesser (1964) and Rehrmann and Pelser (1965) combined a buccal vestibuloplasty using a skin graft with the surgical lowering of the whole floor of the mouth. Hopkins et al (1974, 1980) described the use of a mucosal transposition flap from the lower lip with a skin graft on the donor site and resection of the mylohyoid ridges.
The thickness, appearance, texture and vascularity of skin vary greatly in different parts of the body, and have a strong influence in the selection of donor site appropriate to a particular surgical situation.
The full thickness skin graft may be harvested from a wide selection of donor sites, the main criteria for selection being colour matching, vascularity and the available area of the donor skin.
The posterior surface of the ear extending on to the adjoining post-auricular hairless mastoid skin makes the best donor skin when the face is being grafted. It gives a most excellent skin colour and texture match, and when replacing eyelid skin, is virtually undetectable. The vascularity both of the graft and the usual sites to which it is usually applied make it the easiest of full-thickness skin grafts to get to take. It is the smallness of area of skin available which limits the size of the defect which can be used to cover. The donor site is closed by direct suture.
Upper eyelid skin
In the adult, skin is nearly always available on the upper eyelid, and this can be useful particularly when the defect is of another eyelid. The match of colour and texture is outstandingly good. The area available is obviously limited, though the redundancy of the upper eyelid skin usually present in the older age-group, the group in which such grafts are more often needed, allows more skin to be harvested than one might expect.
The skin of the lower posterior triangle of the neck gives a reasonable colour and texture match used on the face although it is distinctly inferior to post-auricular skin. The larger area of skin is available but unless the neck defect is grafted with a split-skin graft, the increase is not sufficient to make it obviously useful. Grafting the neck creates a cosmetic defect of its own and this is likely to be particularly undesirable in the female where the donor area is often exposed. These adverse factors restrict its usefulness considerably and it is not often used.
The antecubital fossa and the groin are both described as possible donor sites. The dermis is thinner than average, and the skin is mobile on the deeper tissues, but only a limited width is available unless a graft is used to cover the donor site. On the face, the cosmetic result is comparable to that of the supraclavicular skin.
In the antecubital fossa, even if the donor site defect can be closed directly, the resulting scar is very obvious, and if the closure is under much tension, hypertrophy of the scar is a hazard. Its use as a donor site is, therefore, not recommended now. The groin area is useful if a long narrow graft is needed, closure in such circumstances being relatively simple. Its main use is in hand surgery, particularly in managing flexion contractures.
Thigh and abdominal skin
The texture and colour match of thigh and abdominal skin grafted to the face is usually poor. The skin either stays extremely pale or becomes hyperpigmented relative to the rest of the face. An added deficiency is a loss of constantly varying fine play of normal facial expression, the grafted area taking on a rather mask-like appearance, due possibly to its thicker dermis.
Both these sites provide a source of skin for the palm of the hand. The thickness of the dermis in both sites, where there is no ageing skin atrophy, provides a good pad to take the necessary pressure when used on the sole of the foot. If a graft of any size is used, the donor site in its turn must be grafted and even when the donor site can be directly sutured, the scar usually stretches badly.
Split skin grafts
This graft has a much wider usage than the full thickness graft, and within limits, the surgeon is able to control its thickness and make use of that variable in its characteristics and clinical behaviour. The donor site is chosen in any particular instance by taking into account such factors as the amount of skin required, whether a good colour and texture match is possible, local convenience (as in grafting from forearm to hand with need for only one dressing), the necessity of having no hair on the graft, the cutting instrument available, the desirability of avoiding the leg in the aged or out-patient.
The sites usually used as donor sites are:
- the thigh,
- the upper arm,
- the flexor aspect of forearm and
- virtually the whole of the reasonably plane surface of the torso.
When these sites are not available or when all possible sites are needed, skin can be taken from:
- the other aspects of forearm and
- the lower leg.
Harvesting of graft
The full-thickness skin graft is cut with a scalpel while the split-skin graft, of whatever thickness, is usually cut with a special instrument.
Local anaesthesia for graft cutting
Local anaesthesia can be used for harvesting skin grafts by injection of the local anaesthetic agent or by the topical application of the local anaesthetic into the skin area being harvested.
The topical anaesthetic agent commonly used is a mixture of lignocaine and prilocaine. Both agents are very slowly absorbed into the superficial layers of the skin, with negligible absorption into the blood stream, and this allows larger areas to be anaesthetised, though the anaesthesia may not extent to the deeper part of dermis. The area of anaesthesia required is marked out on the skin, and is covered liberally with the anaesthetic cream. As a rule, at least half an hour should be allowed for sufficient absorption to permit the cutting of the graft. Although pallor of the skin area is often seen, it is not a reliable indicator either of the presence of anaesthesia or its surface extent. The patient has to be tested for both.
When the anaesthetic agent is being injected, the addition of hyaluronidase to the solution makes it possible to cut a reasonable size of graft readily. The exact amount of hyaluronidase which has to be used is not critical; 1500 IU added to 100 ml of anaesthetic solution works satisfactorily. The mixture diffuses rapidly and leaves a uniformly flat skin surface. The diffuse increase in tissue turgor also increase the dermal thickness and makes the area slightly more rigid, which is helpful while harvesting thin grafts.
As the full-thickness graft is to be accurately fitted into the defect, a pattern of the defect to be grafted is made to ensure that the graft is at normal skin tension at its new site. Aluminium foil and polythene sheet are the materials most often used for making patterns. The pattern may be made before or after excision. If the defect is irregular, matching points may be tattooed with methylene blue on the defect, and on the graft before it is cut.
While cutting the full-thickness graft with scalpel, it should be carefully cleared of fat on its deeper surface. Time and care should be spent in the cutting of the graft so that no fat is left on its deep surface. This procedure requires both skill and care. Alternatively, the graft may be cut without special regard to the inclusion of fat, the fat being subsequently removed with scissors. This removal of the subcutaneous fat is not considered necessary in case the donor site is upper eyelid or post-auricular region.
The graft is easier to cut if the area is ballooned with fluid, usually I:200,000 noradrenalin. Using the pattern already made, the outline is marked on the skin with methylene blue, and then it is incised and undercut. It often helps to pull the skin of the graft taut over the knife with hooks so that the cutting is done blindly, largely by touch. Alternatively, the graft can be held turned back so that cutting is done under vision. This latter method is less precise and usually results in more fat being left on the graft.
Split skin grafts
Unlike full-thickness grafts, the cutting of split-skin grafts require specialised instruments. The instruments most commonly used are:
- The Humby knife and
- The power-driven dermatome.
The Humby knife
The instrument originally used to cut split-skin grafts was the Blair knife, which has a blade approximately 25 cm long. The difficulty to cut grafts of uniform thickness with this instrument prompted Humby to add a roller mechanism to it. Modified versions of the Humby knife, of which the Watson modification is the most popular, have since been produced. A scaled-down version called the Silver knife, which uses a razor blade to provide the cutting edge, is useful when only a small graft is required. The Humby knife can be used only on convex surfaces, but despite this disadvantage, its convenience makes it the most frequently used instrument for routine graft cutting.
The donor site most often used is the thigh. While positioning the patient, the leg is placed with the appropriate group of muscles relaxed so that by pressing the muscle group either medially or laterally, the maximum of plane surface is presented to the knife. The same principle may be applied to any donor site.
Graft thickness is controlled by adjusting the distance between the roller and the blade. Despite the presence of a gauge on the instrument, most surgeons assess the thickness by holding the knife up to the light to see the clearance between the blade and the roller. Clearance of a little less than 0.5 mm gives a graft of average thickness. This initial assessment is adjusted as necessary by watching both the graft as it is cut, and the bed from which it is being cut.
Ideally, the blade when cutting moves to and fro smoothly over the skin surface which does not move at all with the knife. Drag, resulting from friction between the blade and the skin, causes the skin to move with the blade, making the graft harvesting more difficult. It cannot be completely eliminated, but lubrication with liquid paraffin of the skin surface and the surface of the blade next to the skin reduces it considerably.
The direction and orientation of the cut depends on the convenience of the surgeon. A little in front of the knife and moving smoothly a fixed distance from it, a wooden board is held pressed down on the skin. This serves the dual purpose of steadying the skin and flattening it as the blade reaches it. The edge of this board is also lubricated with liquid paraffin so that the forward movement of the knife is in unison with the movement of the board.
Assessment of graft thickness
Although a setting of the roller is suggested, the surgeon must be prepared to modify it accordingly. The first few millimetres of the graft cut provides an initial indication of the thickness and the setting can be adjusted accordingly.
The translucency of the graft is the main index of its thickness. A very thin graft is so translucent that the grey of the blade shows through. Opacity of the graft increases with increasing thickness until the full-thickness graft has the colour and appearance of cadaveric skin. A split-skin graft of intermediate thickness is of moderate translucency. The pattern of bleeding of the donor site gives a further indication of the graft thickness. The thin graft produces a high density of tiny bleeding points; the thicker graft gives a lower density of larger bleeding points.
The thickness of the skin from the point of view of clinical atrophy and graft cutting, and the presence of remnants of the adnexa from which the sites can heal, vary in different parts of the limb. In general, the skin of the lateral aspect is thicker than the medial, and distal is thicker than proximal. In the thigh when atrophy is clinically obvious, the lateral aspect should be chosen if at all possible.
The power-driven dermatome
The power-driven dermatome is a complex and fragile instrument. It consists of a rapidly oscillating cutting blade which is driven electrically or by compressed air. With the skin held steady, and lubricated with liquid paraffin, the instrument is able to move forward smoothly.
The main advantage of the power-driven dermatome is the ability to cut a graft of controlled width and accurately controllable thickness from almost any part of the trunk or limbs. It is also capable of cutting thin grafts much more consistently when compared to other instruments. The straight margin, and the uniform thickness of the graft which it cuts, means that one need not leave any quantity of skin between adjoining donor sites in the knowledge that the whole area will heal uniformly and quickly. This facility makes it practically possible to cut successive crops of skin from the same donor site, which is a valuable property when the skin is at a premium such as in extensive burns.
Storage of skin
By storage at a low temperature, skin cut in excess of current requirements can be preserved for later use as needed. The increase in the use of ‘delayed exposed grafting’ has greatly increased the need for storage. Within the temperature range 0 –37˚ C, the survival time of a stored graft is a function of its temperature; the lower the temperature, the longer the survival time.
The graft is wrapped in gauze moistened with saline and placed in a sterile, sealed container. Unless specially long survival (e.g. up to 21 days) is needed, the storage temperature is not of paramount importance, but it is generally considered that 4˚ C gives the best results.
Preparation of recipient site
Free skin grafts are applied either to raw surfaces surgically created, or at least surgically clean, or to granulating wounds. The practise of grafting and site preparation varies with the two types of surfaces.
The surgically clean surfaces
A completely dry field is essential before the graft is applied, since graft failure is most often due to the presence of haematoma. To achieve this, several measures are used. Time is the single most important factor in this regard. The steps of the operation should be planned to give the area to be grafted the longest possible time for the normal haemostatic mechanism to become effective. While waiting for bleeding to cease, the area should be left covered with gauze soaked in saline.
Only the actual bleeding point should be picked up by the mosquito forceps so that necrosis caused by the short fine catgut is minimal. Bipolar coagulation is a useful alternative. Once the defect is created, the continuous use of suction would keep the bleeding active. Even when a specific clot is to be sucked off, the suction nozzle should not actually touch the tissue.
After the graft is sutured in place, unless the graft bed is dry, it is a good practise to flush out under the graft with saline using a 20 ml syringe with blunt cannula, before the tie-over bolus is applied.
Healthy granulations are flat, red and vascular, do not bleed unduly readily, are free from a covering surface film, and shows evidence of good marginal healing. Left ungrafted, granulations generally become more fibrous (less vascular) or oedematous. Infection tends to add to the difficulties of grafting.
Systemic antibiotics to which the colonising organisms are sensitive, are ineffective in eliminating them from a granulating surface. An antiseptic (such as chlorhexidene) applied locally is likely to be more effective. The presence of slough created a suitable environment for continuing infection. Surgical excision is a rapid and highly effective method of eliminating it. In the process, excision of fascia is preferable to excision of fat. The Humby knife with the roller widely open may be used to excise both slough and heavily infected granulations.
Granulations, once clean and free of slough, should be grafted without delay. If this is not possible, the area should be kept adequately covered with a large and thick dressing. Crepe bandages may be used to exert pressure over the area. It is noticed that hydrocortisone ointment sometimes improves unhealthy granulations.
Application of the graft
The full-thickness skin graft, cut to its prescribed pattern, fits the defect accurately and is sutured edge to edge along its margin. Sufficient sutures are inserted to give as accurate edge apposition as possible, care being taken to avoid inversion of the edges. Sufficient sutures are left long to provide a snug tie-over, and the remainder are cut short. The spilt-skin graft is cut large enough to cover the defect with an overlap, and the sutures used to hold it in its overlapped position are left long to provide for the tie-over.
The application of a skin graft depend on whether the graft is being applied on the skin surface or inside the mouth and/or sino-nasal cavity, but in any site, two distinct techniques are available. In the first, pressure is applied to the graft; in the second, the graft is left exposed without pressure being applied to the graft.
The skin surface
Pressure methods are preferable when the graft is small in area and are invariable when it is full-thickness in type. They are advisable even if the graft is split-skin when the defect is in an area which is inherently mobile (around eyelids and mouth), where the defect is markedly irregular in contour (the pinna), and when the defect is markedly concave (orbital cavity following exenteration). When grafting is carried out primarily (immediately following the creation of the defect) pressure methods are normally used since the pressure, apart from keeping the graft immobile, helps to achieve hemostasis.
The pressure is exerted on the graft surface by a bolus applied directly over the graft and further pressure may be added by the use of additional dressings and crepe bandage and/or Elastoplast. The pressure is not a necessary factor in the take of the graft, and is only a means of providing immobility of the graft and holding it in contact with the bed.
Various bolus materials are used – flavine wool (cotton wool prepared with flavine emulsion), cotton wool moistened with saline or liquid paraffin, cotton waste, and polyurethane foams are some examples. The bolus should be bulky and extent to the margins of the graft, the long tie-over sutures being then tied tightly over the bolus, anchoring the bolus and graft in a single mass. A layer of Sofra-tulle® laid over the graft before the bolus is applied, might help to ease the first post-operative dressing.
In certain situations, the defect may have to be kept stretched while a split-skin graft is taking. This is to allow as much skin as possible to be introduced into the defect to mitigate the effect of any subsequent graft contracture. The usual bolus materials are not rigid enough to keep the defect stretched and a bolus of dental impression compound may be used instead. Since it softens in hot water bath and hardens to rigidity on cooling, an accurate impression of the stretched defect may be made from it. The material with the graft draped over its surface is then inserted into the defect. The sutures are placed in and along the margins of the defect and tied across the bolus drawing the defect over it and stretching it so that as much skin as possible is inserted. This technique has its main application in the reconstruction of upper eyelid defects.
The outer pressure dressing consists of the usual gauze, cotton wool and crepe bandage or Elastoplast. The bulk of dressing may be enough for immobilisation, but plaster of Paris should always be used if necessary to reinforce the dressings.
The exposed grafting was initially developed as a solution to the ineffectiveness of bolus grafting in areas which cannot be immobilised. In this technique, the graft is laid on the defect, without dressing of any kind, merely protected from being rubbed off, and allowed to attach by fibrin adhesion alone. While applying the graft, any air trapped under it should be pressed out and the skin allowed to overlap the defect margins. Fibrin adhesion occurs quickly and it helps the graft to tolerate minor movements without interfering with the process of graft uptake.
If exposed grafting is used primarily, control of all bleeding points is essential since pressure is not available to help hemostasis. Since this is practically difficult, a technique called ‘delayed exposed grafting’ is used, where the application of the graft is postponed until natural hemostasis has taken place, the skin being stored at a lower temperature in the interval. The waiting period (usually 2-5 days) is used to free the wound of all the residual blood clot, and the graft can be applied as soon as the surface has been cleared of clot. Late exposed grafting, allowing the wound to granulate, is another option, but it has little application in head and neck regions.
In using delayed exposed grafting, the most important factor to be taken care is that the surface of the defect should not be allowed to dry out. This is particularly important when the forehead and the scalp are the sites concerned. For this reason, an occlusive dressing should be applied to the defect as soon as it is created.
Exposed grafting demands a degree of co-operation from the patient, and it has to be used with discretion in children. In the head and neck region, however, no elaborate instructions are usually needed; an explanation to the patient of the need for care is often sufficient.
The procedure of meshing the grafts considerably help to expand the area which an individual graft is able to cover. The graft, cut in the usual way is passed through an instrument from which it emerges shredded into a regular network of skin. An alternative is to manually create regular slits on the graft using a scalpel. Traction applied to the four corners of the graft expands the mesh, giving a considerable increase in area. Apart from the factor that it provides for a large surface area, meshed grafts also show a higher ease of graft uptake. The main disadvantage is the unpredictable cosmetic outcome, making it unpopular in cosmetically important sites. The chief indication of mesh grafting is to expand the extent of the area the graft is being used to cover.
In the mouth, the nasal cavity or the sinuses, pressure methods either involve the use of a bolus tie-over dressing or, when the bed has a firm bony base, the use of a dental appliance to exert pressure on the graft.
This method uses a tie-over bolus in the manner primarily designed for grafting on the skin surface. Unfortunately, with most materials, the bolus rapidly becomes soaked with saliva, food debris, bacteria etc. with resulting offensive smell. Polyurethane foam is considered to be the most suitable bolus material to be used in the mouth. After suturing the graft with sufficient overlap and leaving the sutures long, the surgeon himself compresses the bolus between his fingertips and holds it against the defect, while the assistant completes the tie-over sutures around the bolus. After the compressing finger is removed, the bolus expands to exert its pressure on the graft.
The overlap of the graft may become a difficult slough which may separate spontaneously, but more often it is trimmed off when the bolus is removed 7 days after its insertion. By the time, the part of the graft which is taken, is fixed to the bed. Any area of failure is left to heal spontaneously.
Bolus grafting is most suitable when used in obviously concave areas where mobility is minimal or where the graft bed can provide some stability, as in buccal mucosa or floor of the mouth. It is advisable to insert as much skin as the defect can accommodate to avoid subsequent tenting, and to compensate for graft contraction.
Dental appliance method
This method is used where treatment of the tumour involves resected part of hard palate and upper alveolus. The technique may be discussed under two headings – edentulous and dentulous patients.
In the edentulous patient, an acrylic dental plate is prepared pre-operatively. If the patient already has a denture which fits well, it can be used as well. This provides the basis of the splint which ultimately presses the graft against the bed. The plate fits the area untouched by resection, but a fresh mould of the post-resection defect is required. Dental impression compound and gutta-percha are the available moulding materials for this purpose. Multiple holes are bored in the part of the splint which correspond to the site of the resection at the time of making the splint. Then, a bolus of softened bolus material pressed against it extrudes through the holes, making the two into a single structure once the material cools.
After the defect is created, the splint, with its bolus heated and made malleable once again, is pressed hard into the defect. This gives a composite denture-splint which matches accurately the irregular contours of the post-resection surface. Fixed in this position, it holds the graft firmly against the defect. The methods used to fix the splint can be extra-oral or intra-oral.
Intra-oral fixation may be provided either by direct wiring to the upper alveolus or by wire suspension to the zygomatic arch. Direct wiring to the upper alveolus can be used when there is sufficient alveolus left after resection. Holes are drilled on the splint/ denture as planned and then, with the splint held in position, a curved bone awl is thrust through the upper alveolar bone corresponding to the site of the hole in the splint. A 0.4mm stainless steel wire is used to fix the splint/denture to the alveolar ridge. Zygomatic suspension is required when there is insufficient upper alveolus left after resection. For this method, cleats should be provided on the sides of the splint. With the splint in position, a wire is looped over each zygomatic arch and its ends brought into the oral cavity and fixed firmly to the splint. A splint wired intra-orally is tolerated well and is removed 7–10 days to allow inspection of the graft. Intra-oral fixation should be preferred whenever it is possible, as it is comfortable to the patient and convenient to the surgeon.
Extra-oral fixation is provided by attaching the splint to the skull through a system of universal rods or joints. For this, the splint/denture should be constructed with a metal plate inset in the midline on its anterior surface. Into this, the fixing rod may be screwed. The skull fixation is best provided by supra-orbital pins – rods with self-tapping screws attached to supra-orbital ridges on either side and attached to the intra-oral splint through a rigid connecting rod. Other alternatives, mostly of historical importance include the halo frame and plaster of Paris headcap.
When the patient has teeth, the making of dental splints is more complicated, and cap-splints are used. The teeth outside the line of the mucosal resection are cap-splinted. A screw attachment welded to the cap-splint carries an acrylic plate shaped to correspond roughly to the shape of the alveolar segment to be excised. A bolus of dental compound welded to this plate gives the final accurate splint needed to hold the graft in place. When cap-splints cannot be made or enough teeth are not present, a denture is made with holes to accommodate the remaining teeth. This can then be used as described for the edentulous patient.
The graft can be applied to the defect in two ways
- If the defect is markedly concave, the skin can be draped over the moulded dental compound so that when the splint is wired in position, it carries the graft with it. When this method is used, it is advisable to glue the graft (using skin glue) to the bolus to prevent it from slipping. The adhesion is lost over a few days, and so when the splint is removed at the first dressing, the two surfaces separate easily.
- When the defect is shallow, the graft can be sutured to the margins of the defect with the usual overlap. The dental splint with the bolus is then inserted and fixed in position.
The technical problem posed by exposed grafting inside the mouth is one of providing continuing contact and effective immobility for sufficiently long to allow vascularisation of the graft. This has been largely solved by the use of quilted grafting.
This method was described by McGregor in 1975. Quilted grafting is used in sites which are impossible to immobilise, and it finds its main application in defects of mobile parts of oral cavity, most frequently the side of the tongue. Its successful use has prompted many surgeons to make use of the technique in other intra-oral sites as well.
The split-skin graft is sutured with catgut to the margins of the defect with an overlap in the usual way, and multiple additional sutures are inserted through the graft and the underlying tongue muscle, anchoring them together, and giving the overall appearance of a ‘quilt’. Each quilting suture creates a point of immobile contact between the graft and the bed with a ‘mosaic of squares’, each sufficiently immobile to allow the graft to become vascularised.
As the blind insertion of the quilting sutures inevitably causes some bleeding beneath the graft, multiple slits should be made on its surface to allow for the escape of blood and oedema fluid.
The process of graft take
The graft initially adheres to its new bed by fibrin, and its immediate nutritional requirements are met by diffusion from plasma which exudes from the bed providing the so-called ‘plasmatic circulation’. This is quickly reinforced by the outgrowth of capillary buds from the recipient area to unite with those on the deep surface of the graft and re-establish a circulation of blood in the graft. This link-up is usually well advanced by the 3rd day.
Coinciding with the vascular link-up, the fibrin is infiltrated by fibroblasts which gradually convert the initial tenuous fibrin clot adhesion into a definitive attachment by fibrous tissue. The strength of this attachment increases quickly, providing an anchorage which allows the graft to be handled safely within 4 days. More slowly, a lymphatic link-up is added, and even more slowly, nerve supply is established although imperfectly and variably.
The processes most critical in graft take are revascularisation and fibrous tissue fixation. The speed and effectiveness of these processes are determined by the characteristics of the graft bed, the graft itself, and the conditions under which the graft is applied.
The graft bed
The bed on which the graft is laid must have a rich enough blood supply to vascularise the graft and also be capable of providing the necessary initial fibrin anchorage.
Surfaces which show rapid and profuse outgrowth of capillary buds takes a graft readily. The capability of the surface to produce granulations is a good indicator of graft survival on that surface. The soft tissues of the face, muscle, fascia and fat are so vascular that they all accept grafts readily. Cartilage covered with perichondrium, bone covered with periosteum and tendon covered with paratendon takes skin grafts without difficulty. Bare cartilage and bare tendon cannot be relied upon to take a graft although if the area is too small, the vascularity of the surrounding tissue may be sufficiently profuse to allow the graft to bridge the area and cover it successfully. The bare cortical bone on the outer table of the skull and mandible lack sufficient vascularity to take a graft successfully. The hard palate, the surrounding maxillary bone, the walls of the orbit, the circum-orbital buttresses, and the bone of the diploë (after the outer table of skull is removed) all take up grafts readily. The dura mater, the mucoperiosteum and the mucoperichondrium are other surfaces which could be expected to take a skin graft successfully.
The influence of vascularity on graft take is best illustrated by the effect of radiation. A site with radiation injury is rarely capable of being successfully grafted, despite the fact that in the absence of such injury, it is routinely grafted without difficulty. Ideally, the excision should extent into the normal tissue beyond the radiation damage before the grafting is attempted but this is not always possible. A useful guide is provided by the amount of fibrosis and induration of the bed, and the amount of small vessel bleeding, compared at he time of excision with the amount expected if radiotherapy had not been given.
Any surface with sufficient vascular supply to support a graft has fibrinogen and the enzymes which convert it into fibrin in adequate quantities to provide the necessary adhesion, unless the surface is harbouring pathogens which destroy fibrin (e.g.- Strep. progenies and Ps. aeruginosa).
Skin grafts can vary both in their thickness and vascularity. These variables affect the revascularisation and consequently the ease of take of the graft. The number of cut capillary ends exposed when a thick skin graft is cut, is smaller than with a thin graft. Thus revascularisation is faster with thin grafts, and they tend to be taken easily. Nevertheless, the common head and neck donor sites have a rich blood supply, and even full thickness grafts from these sites compare favourably in their vascular characteristics with thin split skin grafts taken from elsewhere.
Conditions for take
Rapid vascularisation is the most important factor, and the distance to be travelled by the capillaries for the link-up needs to be as short as possible. The graft therefore has to be in the closest possible contact with the recipient bed. The most frequent causes of separation are bleeding from the bed resulting in haematoma, and tenting of the graft when used in concave sites.
The graft has also to lie immobile on the bed until it is firmly attached by fibrous tissue anchorage. The shearing strains which tend to make the graft slide to and fro and prevent capillary link-up are to be avoided.
The phenomenon of bridging
A graft may survive over bare cortical bone, tendon or cartilage, and even if separated from the bed by a clot, provided the area is small enough. In such circumstances, the graft survives solely by bridging, a phenomenon in which vascularisation takes place solely by capillary invasion from the graft bed. In most cases, bridging is strictly limited in area, and beyond this, the graft will not survive.
Healing of donor site
The cutting of a split skin graft leaves variable portions of the pilosebaceous apparatus and the sweat glands in the donor area and from these multiple foci, epithelium spreads until the area is resurfaced with skin. The pilosebaceous remnants are much more active as foci of epithelial regeneration than the sweat gland remnants. The donor site of a thin graft, with its full complement of cut pilosebaceous follicles, heals in approximately 7-9 days, while that of a thick graft, dependent virtually entirely on sweat gland remnants, may take 14 days or more. The quality of healed donor site skin derived solely from the sweat gland remnants is also poorer. Most grafts are of intermediate thickness and leave a percentage of pilosebaceous apparatus, and takes 9-14 days for donor site healing.
If the graft is so thick that no adnexal structures are left in the donor area, or infection in the area destroys any remnants which are left, the surface will granulate, and healing takes place by epithelial migration from the margins. This takes place very slowly and it is always advisable to split-skin graft such sites, particularly if fat is showing to any extent.
The skin of recently healed donor site looks more deeply coloured than normal, the colour slowly fading in time to leave the area paler than normal, often with areas of variation in pigmentation, indicative of the local minor variations in the thickness of the graft cut.
Donor site management
The management of the donor site is a very important, but mostly overlooked aspect of skin grafting. The problems are pain, the provision for an optimal local environment for the healing process, and removal of the dressings.
Pain usually settles in 3-4 days, and is often followed by itching. Although itching is a clinical indicator of satisfactory progress in healing, it causes more discomfort to the patient than pain and is more difficult to treat. Pain can be reduced by peri-operative application of topical local anaesthesia (in the form of jelly), or by impregnating the dressings with some liquid form of anaesthetic agent. Use of a long acting agent often gets the patient over the most painful period without the need to use potent analgesics.
The ideal donor site dressing would remain non-adherent during the healing phase, be absorbent, maintain a moist environment, and minimise the potential for bacterial contamination. Such an ideal dressing does not exist at present. Most cases are managed by dressing with Sofra tulle® (gauze impregnated with liquid paraffin and antibiotic), over which is laden absorbent gauze, the whole held in position with a crepe bandage. The dressing is removed after 10-14 days with care being taken not to disturb the graft.
Newly healed donor sites are often covered with a flaky keratinised layer, and the use of an emollient, non-irritant cream for 3-4 weeks is usually effective.
Skin grafts have several disadvantages when used in oral cavity. They are
- Its colour and texture never match that of normal oral mucosa, although after several years the difference becomes less obvious.
- Unpleasant taste and smell in the absence of adequate hygiene, especially if adnexal structures are included in the graft.
- Poor adhesion of complete dentures when used in the maxilla.
- Scarring and discomfort of donor site.
In order to circumvent these minor drawbacks, mucosal grafts have been introduced to graft intra-oral sites. Mucosal grafts may be full-thickness grafts or split-mucosal grafts.
Full-thickness mucosal grafts
The concept of mucosal grafts was introduced by Peer (1955) who transplanted small areas of oral mucosa on to the conjunctiva. Lewis in 1963 deepened the anterior sublingual area using cheek mucosa, and Propper (1964) reported its application in periodontal surgery. Obwegesser (1965) and Steinhauser (1969) used cheek mucosa in maxillary vestibuloplasty. Robinson (1967) and Hall (1971) recommended keratinised masticatory palatal mucosa as the ideal tissue for denture support because of its similarity to attached gingiva, but the latter reported a troublesome ulceration beneath the denture in the healed donor site in the midline and recommended retaining the central palatine mucosa. Hall and O’Steen (1970) concluded that full-thickness palatal mucosa fulfilled the basic requirements of a skin graft by covering denuded soft tissue while the thick underlying connective tissue layer reduced contraction. The dissection of palatal mucosa was made by free hand between the lamina propria and submucous tissues, leaving the minor salivary glands, fat and neurovascular bundles intact. Guernsey (1973) also preferred palatal mucosa because of its resilience and toughness.
Dekker and Tideman (1973) showed that transplanted cheek mucosa tends to assume the appearance of normal mucosa of the edentulous alveolus. Tideman (1972) noted that taking full-thickness mucosa from the cheek caused post-operative trismus.
Split mucosal grafts
Steinhauser (1969) obtained a split mucosal graft using a mucotome developed from the dermatome (originally devised by Castroveijo in 1959). The advantages claimed for split mucosa included the rapid epithelialisation and scar-free healing of the donor area, the uniform thickness of the graft and reduced contraction at the recipient site. However, he concluded that because of its better stress-bearing capacity and because stability is more important than adhesion in lower jaw, skin is preferable to mucosa in lower labial vestibuloplasty.
Advances in skin grafting
Tissue-cultured skin graft
The development of epidermal culture systems has allowed skin grafting with sheets of cultured keratinocytes. This technique has recently been reviewed by Nanchahal and Ward (1992). It has been found to provide a high expansion factor in the management of burns (O’Connor et al –1981) and chronic ulcers (Leigh et al –1987). Allogenic cultured keratinocytes are rejected, and so autologous cells are necessary to provide permanent epidermal cover.
Application of cultured keratinocytes alone resulted in sloughing, blistering, scarring and wound contraction due to lack of dermal appendages. This led to the development of collagen substrate to support the keratinocytes for grafting. Now autologous keratinocytes are cultured with wide variety of dermal appendages like
- Extruded collagen sheets.
- Reconstituted collagen lattice
- Fibroblast postulated collagen lattices
- Collagen glycosaminoglycan substrates
- Cadeveric dermis
In 1993, Kangesu et al used ‘kerato-dermal grafts’, prepared by combining autologous dermis with cultured keratinocytes, and reported significant improvement in the in vivo growth of the cells.
Donor site dressings
Though split skin graft donor sites have been traditionally dressed with non-occlusive dressings, recent evidence suggest that a moist wound provides a better healing environment. Dressings that provide wounds with a moist environment include semi-permeable films, semi-occlusive hydrogels and occlusive hydrocolloids.
Semi-permeable films are permeable to water vapour and gases including oxygen, but impermeable to water and bacteria. Semi-occlusive hydrogels, while having similar properties, possess an absorbent mechanism. The occlusive hydrocolloids are impermeable to gases, moisture and bacteria. According to Hutchinson (1989), the moist environment beneath these dressings do not encourage wound infection.
Skin graft as interposition material in TMJ ankylosis surgery
The use of skin grafts for arthroplasty dates back to Gluck in 1902. Skin grafts were first used in TMJ ankylosis surgery by Georgiade and Altany in 1957. In 1961, Franchebois and Souyris used a strip of de-epithelialised skin obtained from a full-thickness graft to cover the mandibular stump and obtained good results in 7 patients. In 1977, Popescu and Vasiliu described a full-thickness skin graft technique and reported a low rate of recurrence. Most failures were due either to insufficient availability of skin to cover the tip of the condyle or to the displacement of graft due to poor suturing. Recent studies by Meyer (1988), Kaban et al (1990), Clauser et al (1995) and Chossegros et al (1999) have reported around 90% success rate with inter-incisal width of more than 30 mm after one year follow-up. All these studies reported a low incidence of complications related to infection and inflammation.
Skin grafts have been used in a wide variety of clinical applications for a long time. The main indication is to provide a natural coverage to the raw areas left behind by surgical excisions, burns, ulcers etc. A good clinical assessment and meticulous technique can provide an adequate coverage in such cases. Of late, the applications of skin grafting have grown into new arenas like pre-prosthetic surgery and TMJ ankylosis surgery. With the emergence of recent advances, one can now hope to provide the patient with a near-perfect natural wound cover.
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