You are in: eMedicine Specialties > Plastic Surgery > SKIN Skin, GraftsArticle Last Updated: Feb 17, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Don R Revis Jr, MD, Consulting Staff, Department of Surgery, Division of Plastic and Reconstructive Surgery, University of Florida College of Medicine Don R Revis, Jr, is a member of the following medical societies: American College of Surgeons, American Medical Association, American Society for Aesthetic Plastic Surgery, and American Society of Plastic Surgeons Coauthor(s): Michael Brent Seagle, MD, Associate Professor, Division of Plastic Surgery, University of Florida College of Medicine; Consulting Staff, Florida Surgical Center Editors: Shahin Javaheri, MD, Chief, Department of Plastic Surgery, Martinez Veterans Affairs Outpatient Clinic; Consulting Staff, Advanced Aesthetic Plastic & Reconstructive Surgery; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Wayne Stadelmann, MD, Stadelmann Plastic Surgery, PC; Nicolas (Nick) G Slenkovich, MD, Practice Director, Colorado Plastic Surgery Center at Swedish Medical Center; Susan E Downey, MD, Clinical Associate Professor, Department of Surgery, Division of Plastic Surgery, University of Southern California Author and Editor Disclosure Synonyms and related keywords: skin grafts, skin graft, skin grafting, graft harvesting, split-thickness grafts, full-thickness grafts, dermis, epidermis, wound care, graft survival, revascularization INTRODUCTIONSection 2 of 10
  Skin covers the entire external surface of the human body and is the principle site of interaction with the surrounding world. As such, it performs a multitude of specialized functions. It serves as a protective barrier preventing internal tissues from exposure to trauma, radiation, temperature changes, and infection. Other important functions include thermoregulation, through sweating and vasoconstriction or vasodilatation, and control of insensible fluid loss. Restoration of an intact barrier is of critical importance following wounding and may be achieved in numerous ways, including grafting. Skin grafting was performed in India 2000 years ago, but widespread interest did not develop until the 19th century. Over the last 100 years, skin grafting has evolved into an essential component of the surgeon's armamentarium. The multitude of uses include accelerated healing of burns and other wounds, reduction of scar contracture, enhancement of cosmesis, reduction of insensible fluid loss, and protection from bacterial invasion. The skin varies in thickness depending on anatomic location, sex, and age of the individual. Skin is thickest on the palms and soles of the feet, while the thinnest skin is found on the eyelids and in the postauricular region. Male skin is characteristically thicker than female skin in all anatomic locations. Children have relatively thin skin that progressively thickens until the fourth or fifth decade of life when it begins to thin. This thinning is primarily a dermal change, with loss of elastic fibers, epithelial appendages, and ground substance. As with any procedure, before undertaking skin grafting one must possess a thorough understanding of the pertinent anatomy. The skin consists of 2 layers, the epidermis and dermis. Epidermis The epidermis, the more external of the 2 layers, is a stratified squamous epithelium consisting primarily of keratinocytes in progressive stages of differentiation from deeper to more superficial layers. The epidermis has no blood vessels, thus it must receive nutrients by diffusion from the underlying dermis through the basement membrane, which separates the 2. Dermis The dermis is a more complex structure and is composed of 2 layers, the more superficial papillary dermis and the deeper reticular dermis. The papillary dermis is thinner, consisting of loose connective tissue containing capillaries, elastic fibers, reticular fibers, and some collagen. The reticular dermis consists of a thicker layer of dense connective tissue containing larger blood vessels, closely interlaced elastic fibers, and coarse, branching collagen fibers arranged in layers parallel to the surface. The reticular layer also contains fibroblasts, mast cells, nerve endings, lymphatics, and some epidermal appendages. Surrounding the components of the dermis is the gel-like ground substance composed of mucopolysaccharides (primarily hyaluronic acid), chondroitin sulfates, and glycoproteins. Epithelial cell sources Epidermal appendages are important as a source of epithelial cells that re-epithelialize when the overlying epithelium is removed or destroyed in patients with partial thickness burns, abrasions, or split-thickness skin graft harvesting. These intradermal epithelial structures, such as sebaceous glands, sweat glands, and hair follicles, are lined with epithelial cells with the potential for division and differentiation. They are found deep within the dermis and in the subcutaneous fat deep to the dermis. This accounts for the remarkable ability of the skin to re-epithelialize even very deep cutaneous wounds that are nearly full thickness. Sebaceous glands Sebaceous glands, or holocrine glands, secrete sebum, which serves to lubricate the skin and make it more impervious to moisture. They are found over the entire surface of the body except the palms, soles, and dorsum of the feet. They are largest and most concentrated in the face and scalp where they are the site of origin of acne. Sweat glands Sweat glands, or eccrine glands, are found over the entire surface of the body except the lips, external ear canal, and labia minora. They are most concentrated in the palms and soles of the feet. The normal function of the gland is to produce sweat, which cools the body by evaporation. Apocrine glands Apocrine glands are similar in structure but not identical to the eccrine sweat glands. They are concentrated in the axillae and anogenital regions. They probably serve a vestigial sexual function because they produce odor and do not function prior to puberty. Hair follicles The hair follicle is another important source of epithelial cells, and many of the other epidermal appendages actually open into the hair follicle rather than directly onto the skin surface. GRAFT SELECTIONSection 3 of 10
Skin transplanted from one location to another on the same individual is termed an autogenous graft, or autograft. These consist of the entire epidermis and a dermal component of variable thickness. If the entire thickness of the dermis is included, the appropriate term is full-thickness skin graft. If less than the entire thickness of the dermis is included, appropriate terms are partial or split-thickness skin graft. Split-thickness skin grafts are further categorized as thin (0.005-0.012 inches), intermediate (0.012-0.018 inches), or thick (0.018-0.030 inches) based on the thickness of graft harvested. The thicker the dermal component, the more the characteristics of normal skin are maintained following grafting. This is because of the greater collagen content and the larger number of dermal vascular plexuses and epithelial appendages contained within thicker grafts. However, thicker grafts require more favorable conditions for survival because of the greater amount of tissue requiring revascularization. The choice between full- and split-thickness skin grafting depends on wound condition, location, and size as well as aesthetic concerns. Full-thickness skin grafts Full-thickness skin grafts are ideal for visible areas of the face that are inaccessible to local flaps or when local flaps are not indicated. Full-thickness grafts retain more of the characteristics of normal skin including color, texture, and thickness when compared with split-thickness grafts. Full-thickness grafts also undergo less contraction while healing. This is important on the face as well as on the hands and over mobile joint surfaces. Full-thickness grafts in children are more likely to grow with the individual. However, full-thickness skin grafts are limited to relatively small, uncontaminated, well-vascularized wounds and thus do not have as wide a range of application as split-thickness grafts. Donor sites must be closed primarily or, more rarely, resurfaced with a split-thickness graft from another site. Split-thickness skin grafts Split-thickness skin grafts can tolerate less ideal conditions for survival and have a much broader range of application. They are used to resurface large wounds, line cavities, resurface mucosal deficits, close donor sites of flaps, and resurface muscle flaps. They also are used to achieve temporary closure of wounds created by the removal of lesions that require pathologic examination prior to definitive reconstruction. Split-thickness skin graft donor sites heal spontaneously with cells supplied by the remaining epidermal appendages, and these donor sites may be re-harvested once healing is complete. Split-thickness grafts also have significant disadvantages that must be considered. Split-thickness grafts are more fragile, especially when placed over areas with little underlying soft tissue bulk for support, and usually cannot withstand subsequent radiation therapy. They contract more during healing, do not grow with the individual, and tend to be smoother and shinier than normal skin because of the absence of skin appendages in the graft. They tend to be abnormally pigmented, either pale or white, or alternatively hyperpigmented, particularly in darker-skinned individuals. Their lack of thickness, abnormally smooth texture, lack of hair growth, and abnormal pigmentation make these grafts more functional than cosmetic. When used to resurface large burns of the face, split-thickness grafts may produce an undesirable masklike appearance. Finally, the wound created at the donor site from which the graft is harvested is often more painful than the recipient site to which the graft is applied. DONOR SITE SELECTIONSection 4 of 10
Selection of the donor site is usually based on the features wanted at the recipient site. This is more important in full-thickness grafts, because more of the characteristics of the donor site skin will be retained by the grafted material in its new location. Thickness, texture, pigmentation, and presence or absence of hair should be matched as closely as possible. When grafting in children, consider that donor sites such as the groin, axillae, thigh, and chest will grow hair at puberty, and this hair growth may be undesirable at the new location. Donor sites for full-thickness grafts also are chosen to be inconspicuous and easily closed primarily. Full-thickness grafts may be harvested from the upper eyelid, nasolabial fold, pre- and postauricular regions, and the supraclavicular fossa. These donor sites most often are employed to close a wound on the face or neck. When harvesting from the face, it is often aesthetically preferable to harvest bilaterally to maintain facial symmetry, even if the result is more skin being removed than is necessary to cover the defect. Consider the aesthetic units of the face when excising lesions and applying skin grafts. Incisions should be placed along the borders of aesthetic units rather than across them. When excising lesions from the face, the best results often are obtained by excising a complete aesthetic unit and replacing it with a skin graft, even if this increases the amount of skin removed when compared to what is needed for adequate margins around the excised lesion. Less frequently used full-thickness donor sites include hairless groin skin, dorsum of the foot, wrist flexion crease, and elbow crease. Scars from skin grafts harvested from the wrist flexion crease may resemble those observed with a previous suicide attempt and probably should be avoided. Thick hairless glabrous skin for resurfacing the hand can be taken from the ulnar border of the hand and the sole of the foot with excellent match of color, texture, and thickness. Darker pigmented grafts may be obtained from the prepuce, scrotum, and labia minora. An often overlooked potential donor site for full- or split-thickness grafts is avulsed or surgically removed skin. Split-thickness skin grafts may be harvested from any surface of the body, but sites should be chosen that are easily concealed in recreational clothing. Common sites include the upper anterior and lateral thigh. The buttocks may be used as a donor site, but the patient may complain of significant postoperative pain and will require assistance caring for the wound. The scalp is used for resurfacing areas of the face too large for a full-thickness graft and is especially useful in severe burns with limited donor site availability. Because of its thickness, scalp skin may be repeatedly harvested with almost no risk of alopecia or subsequent hair growth at the recipient site. For hand wounds, the upper inner arm is a cosmetically appealing donor site. WOUND PREPARATIONSection 5 of 10
The most critical component of successful skin grafting is preparation of the recipient site. Physiologic conditions must be optimized to accept and nourish the graft. Skin grafts will not survive on tissue without blood supply, such as bone devascularized by removal of the periosteum, cartilage without the perichondrium, tendon without peritenon, and nerve without perineurium. Skin grafts will survive on periosteum, perichondrium, peritenon, perineurium, dermis, fascia, muscle, and granulation tissue. Wounds secondary to irradiation have a poor blood supply and are unlikely to support a graft. Patients with wounds resulting from venous stasis or arterial insufficiency need to have the underlying condition treated prior to grafting to increase the likelihood of graft survival. The wound also must be free of necrotic tissue and relatively uncontaminated by bacteria. Bacterial counts greater than 100,000 per square centimeter are associated with a high likelihood of graft failure. To achieve an adequate wound bed, debridement, dressing changes, and topical or systemic antibiotics may be indicated prior to grafting. OPERATIVE TECHNIQUESection 6 of 10
Careful operative technique is important for graft survival. After administering appropriate local, regional, or general anesthesia, prepare the wound for grafting. This includes cleansing of the wound with saline or dilute Betadine, judicious debridement, and achievement of meticulous hemostasis. Good hemostatic control can be gained with ligation, gentle pressure, application of a topical vasoconstrictor such as epinephrine, or electrocautery. Electrocautery should be minimized as it creates devitalized tissue. The use of topical or injected epinephrine at the donor or recipient site does not compromise graft survival. Full-thickness skin grafts Full-thickness skin grafts are harvested with a scalpel. The wound is measured, a pattern is made, and the pattern is outlined over the donor region. The pattern should be enlarged by 3-5% to compensate for the immediate primary contraction that occurs because of the elastic fibers contained in the graft dermis. The donor site then may be infiltrated with local anesthetic with or without epinephrine. Infiltration should be performed after the outline of the graft has been drawn on the skin to avoid distortion caused by the infiltrated volume. After incising the pattern, the skin is elevated with a skin hook keeping a finger of the nonoperating hand on the epidermal side of the graft. This provides tension and a sense of graft thickness while the operating hand dissects the graft off the underlying subcutaneous fat. Any residual adipose tissue must be trimmed from the underside of the graft, because this fat is poorly vascularized and will prevent direct contact between the graft dermis and the wound bed. Trimming of residual subcutaneous fat is best accomplished with a sharp, curved scissor with the graft stretched over the nonoperating hand until only the white, glistening dermis remains on the deep surface. The donor site is then closed primarily with excision of "dog ears" if necessary. Split-thickness skin grafts Split-thickness grafts may be harvested in several ways. Blade dermatomes The most common technique involves use of a blade dermatome, which provides rapid harvest of large grafts of uniform thickness. Dermatomes may be air powered, electric, or manually operated. Commonly used dermatomes include the Castroviejo, Reese, Padgett-Hood, Brown, Davol-Simon, and Zimmer. All of these harvest by the same mechanism: a rapidly oscillating side-to-side blade is advanced over the skin with thickness and width settings adjusted by the surgeon. Regardless of the instrument used, adequate anesthesia must be established, because harvesting of skin grafts is a painful procedure. Lidocaine with epinephrine injected at the donor site may reduce blood loss and provide greater tissue turgor, which assists in harvesting. Drum dermatomes Drum dermatomes (Reese, Padgett-Hood) are less frequently used today but are available for specialized grafting needs. On these instruments, the oscillating blade is manually powered as the drum is rolled over the skin surface. These dermatomes can be used to harvest broad sheets of skin of exacting thickness. They are useful when the donor site is irregular, with a convexity, concavity, or bony prominence (neck, flank, buttock), because the skin to be harvested is first made adherent to the drum with a special glue or adhesive tape. These dermatomes also allow precise irregular patterns to be harvested by varying the pattern of adhesive applied to the skin and drum. Free-hand Another method for harvesting split-thickness grafts is free-hand with a knife. Although this may be performed with a scalpel, other devices such as the Humby knife, Weck blade, and Blair knife also are available. The disadvantages include grafts with irregular edges and varying thicknesses. As with the drum dermatomes, greater technical expertise is necessary, and graft quality tends to be more operator dependent when compared to air- or electric-powered dermatomes. Air- and electric-powered dermatomes When using the air or electric powered dermatomes, the operating surgeon must be familiar with the installation of the blade and how to adjust the setting for graft thickness and must check these before operating the device. There is a correct and an incorrect orientation of the blade, and the 2 may easily be confused by inexperienced operating room personnel. Insertion of a No. 15 blade scalpel simulates a thickness of 0.015 inches and can be used to check that thickness settings are uniform and correct. After the blade orientation, width guard and depth setting are confirmed, and harvesting may begin. Harvesting Betadine or another solution may have been used to sterilize the donor site at the beginning of the procedure and should be washed off. Duraprep should not be used to prepare a donor site because its removal is difficult. It is useful to lubricate the skin and dermatome with mineral oil or pHisoHex to facilitate easy gliding of the dermatome over the skin. These may be gently washed from the skin graft with saline following harvesting and do not compromise graft survival. The dermatome is held in the dominant hand of the operator at a 30-45° angle from the donor skin surface. Greater angulation of the dermatome leads to gouging or trenching of the donor site skin. With the nonoperating hand providing traction behind the dermatome and the assistant providing traction in front of the dermatome, the dermatome is activated and advanced in a smooth, continuous motion over the skin with gentle downward pressure. After the appropriate length has been harvested, the dermatome is tilted away from the skin and lifted off the skin to cut the distal edge of the graft and complete the harvesting. The graft then may be gently washed to remove the lubricant and wrapped in a moistened saline sponge until it is ready to be used. The donor site typically has numerous small punctate bleeding spots with thin-to-intermediate thickness grafts; thicker grafts have fewer, larger bleeding points that bleed more briskly. Any exposure of fat indicates that excision of the graft was performed too deeply, probably because of technical error in assembly of the dermatome. Meshing Once harvested, a split-thickness skin graft may be meshed by placing the graft on a carrier and passing it through a mechanical meshing instrument. This technique allows expansion of the surface area of the graft up to 9 times the surface area of the donor site. This technique is useful when insufficient donor skin is available for a large wound, such as in major burns or when the recipient site is irregularly contoured and uniform adherence of a solid sheet is a concern. The slits in the meshed skin graft allow wound fluid to escape through the graft rather than accumulating beneath it and preventing adherence. However, the expansion slits will not prevent graft loss from underlying hematoma. The expansion slits must heal by re-epithelialization and may contract significantly. When healed, the grafted site characteristically has a "crocodile skin" or "checkerboard" appearance. Because of the secondary contraction and poor cosmesis with this technique, it should be avoided over joints and in the face, hands, and other highly visible areas. In these regions, a split- or full-thickness sheet graft may be "pie-crusted" to allow egress of wound fluid from beneath the graft. This technique involves making multiple stab wounds through the graft with a No. 15 scalpel blade; it does not serve to expand the surface area of the graft. Inserting graft Once the graft has been harvested, the recipient site should be re-inspected for hemostasis. Once this is complete, the graft may be placed on the wound bed. Attention must be paid to placing the dermal side down. Although this sounds simple and obvious, dermis and epidermis can appear very similar without close inspection in lighter-skinned individuals. Care also should be taken to prevent wrinkling or excessive stretching of the graft. The graft must then be secured in place to provide stability during initial adherence and healing. This is most often accomplished by suturing or stapling the graft to the skin surrounding the wound bed. Staples are especially useful when the wound is deeper than the surface of the surrounding skin, since they can be inserted in a way that keeps the graft adherent to the bed and to the vertical walls of the wound. However, staples are painful to remove and may disrupt adherence of the graft to the wound when removed approximately 7-10 days postoperatively. Absorbable sutures are useful because they do not require removal. Usually 4 "corner" sutures are placed to hold the graft in the proper orientation, then a running suture is placed around the periphery. It is helpful to pass the needle first through the graft then through the surrounding wound margin to prevent lifting of the graft from the wound bed. Perfect epidermal to epidermal approximation ensures optimal cosmetic results, and the sutures should approximate, not strangulate the skin edges. Occasionally central sutures, termed quilting sutures, are used to ensure adherence of the graft over a concave portion of the wound, but these are not routinely necessary. Dressing A dressing is chosen to provide uniform pressure over the entire grafted area with a nonadherent, semiocclusive, absorbent dressing material. These dressings are intended to immobilize the graft, prevent shearing, and prevent seroma or hematoma formation beneath the graft.
Fibrin makes grafts adherent within 6-8 hours after grafting, but the initial dressing should be left in place for approximately 5 days (3-7 days) unless there is pain, odor, discharge, or other sign of a complication. When removing dressings, the dressing material should be moistened with saline to reduce adherence to the graft. The dressing is then removed carefully to prevent lifting the graft off the underlying wound bed. A hematoma or seroma encountered at the dressing change should be treated by making a small incision directly over the collection and expressing the underlying contents. Rolling or pushing fluid out under the edge of the graft is not recommended, because it disrupts the adherence of the entire graft, not just the limited area of hematoma or seroma formation. Donor site dressing options The donor site also must be dressed appropriately at the conclusion of a skin graft operation. Full-thickness donor sites closed primarily are dressed as are other wounds closed primarily. A variety of dressing options exist for split-thickness skin graft donor sites. Achieving hemostasis can be facilitated with the application of a moist gauze containing epinephrine solution. The ideal donor site dressing is one that promotes rapid re-epithelialization, causes little pain, requires little care, is inexpensive, and has a low rate of infection. Options include occlusive dressings (Duoderm), semi-occlusive dressings (Op-Site, Tegaderm), semi-open dressings (Vaseline gauze, Xeroform or scarlet red), and no dressing.
Donor sites for split-thickness grafts heal spontaneously from epithelial cells remaining in epithelial appendages within the dermis and at the wound edges. Healing begins within 24 hours of harvesting, and the rate of healing is directly proportional to the number of epithelial appendages remaining and inversely proportional to the thickness of graft harvested. When the epidermis has regenerated it may be reharvested; however, each harvesting removes a portion of dermis that is not regenerated. The initial epithelium that is regenerated is very delicate and easy to disrupt with tape or dressing changes. This is another reason to use the semi-occlusive dressing technique that does not need to be removed until healing is complete. Finally, hyperpigmentation may persist for many months following donor site healing, and some individuals may develop hypertrophic scarring or even keloids at the site. GRAFT SURVIVAL AND HEALINGSection 7 of 10
Initial adherence After graft placement, there is an initial adherence to the wound bed via a thin fibrin network that temporarily anchors the graft until definitive circulation and connective tissue connections are established. This adherence begins immediately and is probably at its maximum by 8 hours postgrafting. Plastic imbibition The period of time between grafting and revascularization of the graft is referred to as the phase of plasmatic imbibition. The graft imbibes wound exudate by capillary action through the spongelike structure of the graft dermis and through the dermal blood vessels. This prevents graft desiccation, maintains graft vessel patency, and provides nourishment for the graft. This process is entirely responsible for graft survival for 2-3 days until circulation is reestablished. During this time, the graft typically becomes edematous and increases in weight by 30-50%. Revascularization Revascularization of the graft begins 2-3 days postgrafting by a mechanism not completely understood. Competing theories exist, and the true mechanism may be a combination of 2 or 3 of these theories. Inosculation is the establishment of direct anastomoses between graft and recipient blood vessels. Others have demonstrated vascular ingrowth of recipient bed vessels into the graft along the channels of previous graft vessels, a similar but not identical theory to inosculation. Still others propose random new vascular ingrowth of recipient bed vessels into the graft without regard for previous graft vessels. Regardless of the true mechanism(s), full circulation to the graft is restored by 6-7 days postgrafting. Without initial adherence, plasmatic imbibition, and revascularization, the graft will not survive. Wound contraction Several important aspects of skin graft healing deserve further discussion. Wound contraction may produce serious functional and cosmetic problems depending on location and severity. On the face, contraction may produce ectropion, retraction of the nasal ala, or distortion of the vermillion border. Over joints, contraction may limit functional range of motion. Contraction probably begins shortly after initial wounding and progresses slowly for 6-18 months following skin grafting. The wound bed is the locus of the contractile forces, and the myofibroblast in the wound bed is believed to be responsible for this contraction. In general, wounds covered with full-thickness grafts contract less than those covered with split-thickness grafts, and those covered with thick split-thickness grafts contract less than those treated with thin split-thickness grafts. Furthermore, wounds covered with thin split-thickness skin grafts contract less than open wounds. The ability of a skin graft to resist contraction is related to the thickness of deep dermal component included in the graft, not just the absolute thickness of the graft. This deep dermal component is able to suppress myofibroblast function by an unknown mechanism. Contraction can be ameliorated by splinting or compression devices such as facial masks or elastic compression garments. These devices should be worn as much as tolerated each day for at least the first 6 months after grafting and often even longer. Regeneration Epithelial appendages need to regenerate after grafting. Hair rarely grows from split-thickness grafts unless the grafts are quite thick. Hair is likely to grow from full-thickness grafts, and to be sure this can be desirable. One must select donor sites for full-thickness grafting with awareness of the patterns of hair growth at the present time and in the future of the individual. When deliberately grafting hair follicles, as in scalp hair restoration for alopecia or eyebrow or eyelash reconstructions, carefully angle the scalpel blade to incise the skin parallel to the orientation of the hair follicles. These structures usually are not oriented parallel to the skin surface and will be transected if the incision is not beveled in an oblique direction. Sweat glands and sebaceous glands initially degenerate following grafting. Once again, they are more likely to regenerate in full-thickness grafts, because they are transferred as an entire functional unit. In split-thickness grafts, only a portion of the gland is transferred, and the remaining portion may not regenerate. Sweat gland regeneration is dependent on reinnervation of the skin graft with recipient bed sympathetic nerve fibers. Once this ingrowth has occurred, the skin graft assumes the sweating characteristics of the recipient site rather than retaining the characteristics of the donor site. Sebaceous gland regeneration is independent of graft reinnervation and retains the characteristics of the donor site. Prior to regeneration, a skin graft lacks the normal lubrication of sebum produced by these glands. This makes the grafts more susceptible to injury. The grafts may appear dry and scaly during this period. Patients frequently complain of pruritus. Bland creams, such as lanolin or cocoa butter, should be recommended to the patient to moisturize the graft and reduce itching. Unfortunately this condition often persists in thin split-thickness grafts, whereas full-thickness grafts become more soft and pliable as sebaceous gland regeneration occurs. These glands also may regenerate on the deep surface of skin grafts and present as tiny white inclusions termed milia. When this occurs they can be unroofed with a needle. Reinnervation Reinnervation of the graft occurs from the recipient bed and the periphery along the empty neurolemmal sheaths of the graft. Sensibility returns to the periphery of the graft and proceeds centrally. This process usually begins during the first month but is not complete for several years following grafting. As reinnervation occurs, pain is usually the first perceived sensation followed later by touch, heat, and cold. Split-thickness grafts are reinnervated more quickly, but full-thickness grafts are reinnervated more completely. Reinnervation is always incomplete, and some degree of derangement is permanent. Usually the patient develops protective sensation but not normal perception. Pigmentation Pigmentation returns gradually to full-thickness skin grafts, and they maintain a pigment similar to the donor site much more predictably than split-thickness grafts. Split-thickness grafts may remain pale or white or may become hyperpigmented with exposure to sunlight. It is generally recommended that the graft be protected from direct sunlight for at least 6 months after grafting or even longer. Hyperpigmentation that is a problem has been treated with dermabrasion and laser resurfacing with varying success. GRAFT FAILURESection 8 of 10
Skin grafting may fail for numerous reasons. The most common reason for skin graft failure is poor graft contact or adherence to the recipient bed. Hematoma beneath the graft or seroma formation may prevent graft contact and adherence to the underlying wound bed, depriving the graft of necessary nourishment. Movement of the graft, or shear forces, also may cause graft failure by disrupting the fragile attachments of the graft to the wound bed. Another common source of failure is a poor recipient site. The wound may have poor vascularity, or the surface contamination may have been too great to allow graft survival. Bacteria and the response to bacteria through cellular and humoral immune responses lead to the release of proteolytic enzymes and other inflammatory products at the wound interface that disrupt the fibrin adherence of the graft. Technical error also may cause graft failure. Applying the graft upside down results in complete graft loss. Applying excess pressure, stretching the graft too tightly, or other traumatic handling of the graft can cause partial or complete graft failure. BIOLOGIC SKIN SUBSTITUTESSection 9 of 10
No discussion of skin grafting would be complete without mentioning the alternative substances now available. These biologic skin substitutes may be intended for permanent replacement or as a temporary biologic dressing until a permanent solution is available or normal skin regeneration and healing occur. These skin substitutes serve multiple functions. They decrease the bacterial count and promote a sterile wound; they slow the loss of water, protein and electrolytes; they reduce pain and fever, help restore function, facilitate early motion, and provide coverage of vessels, tendons, and nerves to prevent desiccation. The ideal skin substitute is nontoxic, has little or no antigenicity, is immunologically compatible, and does not transmit disease. Cadaveric grafts and porcine grafts are skin substitutes that have been used clinically for several decades. Cadaveric grafts are termed allografts, or homografts, because they are transplanted from one individual to another within the same species. Pig skin grafts are termed xenografts, or heterografts, because they are transplanted from an organism of one species to that of a different species. These may be prepared for use in several ways. They may be treated with glycerol and rapidly frozen with liquid nitrogen or they may be lyophilized and freeze-dried. Although cell viability is not preserved through the processing of these grafts, the structural details, proteins, and enzymes remain intact. Eventually rejected by the body, cadaveric and pig skin may be used as temporary biologic dressings. They are especially useful in extensive burns where skin graft donor sites are limited. In the average patient, these must be changed every 3 days to prevent a rejection response, but the relatively immunosuppressed burn patient may require removal only every 5 days. The theoretical risk of disease transmission with cadaveric grafts also exists. Epithelial cells Epithelial cells can be grown in culture for use as both autografts and allografts. Cultured epithelial autografts require taking biopsy-sized excisions of cells from the patient and then growing these cells in culture medium. For this reason, they are not available for several weeks until they have grown to confluent sheets. This culturing process is currently quite costly and yields an extremely fragile sheet of cells that are very sensitive to infection. Allograft sheets can be kept available in skin banks but share the structural weaknesses of autografts as well as the theoretical risk of disease transmission. These cultured allografts are eventually rejected as well, but in the interim can serve as a biologic dressing. Allograft dermis Allograft dermis also has been developed. This structure is not actually rejected by the body, because it is rendered relatively immunologically inert during processing. The body instead remodels and replaces it with native dermis. Cultured epithelial sheets or thin split-thickness grafts may be placed over a dermal substitute once it has become incorporated. Bilayer collagen matrices Bilayer collagen matrices are the latest development in this innovative field. These consist of a porous, spongelike lattice of bovine collagen, chondroitin-6-sulfate, and glycosaminoglycans that serves as the dermal substitute. This dermal substitute layer acts as a scaffold for the ingrowth of native fibroblasts and blood vessels that eventually replace it. An overlying silicone membrane simulates the epidermis and serves to seal the surface to reduce insensible fluid loss. This membrane is transparent, allowing wound inspection, and progressively becomes less adherent to the dermal layer as it is incorporated by the body. At approximately 3 weeks, the silicone layer may be peeled off and replaced with cultured epithelial cells or thin split-thickness skin grafts. Conclusion It is likely that current research in molecular biology, wound healing, and immunology will yield even better skin substitutes with which to treat patients in the future. One can envision a time when a synthetic bilayer membrane with qualities equivalent to those of normal skin will be readily available off the shelf, with an application process no more difficult than a dressing change. REFERENCESSection 10 of 10
Article Last Updated: Feb 17, 2006 |
