Continuing Education Activity

Skin grafting is a procedure that is essential to reconstructive surgery for patients who have suffered burns, traumas, and non-healing or large wounds. This skill is necessary to provide improved quality of life for patients with significant wounds and extensive burns. This activity reviews the indications for skin grafts, the preparation of the wound bed, and the steps required to perform successful wound grafting. It explains the role of the interprofessional team in managing care for patients with burns and large or non-healing wounds.

Objectives:

• Describe the different types of wound grafts that are available as either temporary dressings or for permanent healing.
• Review the steps that are taken to ensure a wound bed is appropriately prepared for grafting.
• Outline the methods and tools used to harvest both full-thickness and split-thickness skin grafts.
• Explain the importance of early eschar removal and wound grafting for overall patient health.

Introduction

Skin grafting is a procedure that is essential to reconstructive surgery for patients who have suffered burns, traumas, and non-healing or large wounds. This skill is necessary to provide improved quality of life for patients with significant wounds and extensive burns. Even more important than cosmesis is reestablishing the continuity of the skin to provide protection for the body.[1]

Xenografts are harvested from different species, the most common of these are porcine, and they are used as temporary bandages on wounds. They will not revascularize. The next type of graft is an allograft. These are cadaveric skin grafts taken from organ donors. They are ideal biologic dressings for patients who need resuscitation and continued debridements of the wound bed to ensure that it will accept an autograft.[2][3] Allografts will undergo revascularization in the initial period. The body’s host defenses will eventually reject both of these types of grafts. Autografts are skin grafts that are taken from the patient. In this case, antigenic compatibility is not an issue and will allow for permanent skin healing. This is often the final stage of wound healing after extensive debridement to ensure that the wound bed is healthy.[4][5]

In addition to the different types of skin grafts available, there are also skin substitutes. One of the major limitations of skin substitutes is the associated cost. A majority of the available products provide either epidermis or dermis. The lack of dermis and subcutaneous tissue in epidermis substitutes results in a lack of elasticity and strength. Dermal layer products do not have epidermal coverage and depend on a long period of epidermal in-growth to effectively cover the wound.

Currently, the most commonly used skin substitute is a cultured epidermal autograft (CEA). A full-thickness skin biopsy from the patient is obtained, and the keratinocytes are then used to develop a graft by expanding the cells into a neoepidermis. These grafts are even more delicate than autografts, they are extremely susceptible to shear injuries, and after they are incorporated, they remain fragile and require longer periods of immobility to ensure they are not damaged.[6][7]

Dermal substitutes are composed of a matrix of glycosaminoglycans and collagen. Alloderm is a popular dermal substitute that is obtained from cadaveric allografts. It has had good cosmetic outcomes in several studies with small populations, but extensive costs have limited widespread use and studies.[7][8] 

A newer therapy product requires a biopsy from the dermal-epidermal junction to produce autologous cells (keratinocytes, fibroblasts, melanocytes) that are delivered in a suspension. This suspension is then applied to the wound by spraying it on the wound. Integra is a bilayer product composed of bovine collagen and glycosaminoglycans with a silicone sheet that acts as an epidermis for 2 to 3 weeks while the allograft degradation matrix occurs. As neovascularization occurs, the matrix degrades and is replaced by a collagen matrix produced by the patient's body. The silicone is then removed and replaced with a split-thickness skin graft (STSG). This product is used to reduce the amount of skin surface area needed for the eventual STSG.[9] Several other options are currently being developed and are under investigation. These products are accompanied by a high cost, and more research is necessary to confirm good cosmetic outcomes and long-term wound coverage.[7]

Indications

Indications of skin grafting include deep second or third-degree burns, traumas, and non-healing or large wounds that will not close via primary or secondary intention. Patients who may benefit from skin grafts include burn patients, patients with non-healing wounds, such as diabetic foot wounds, or patients who have had to undergo extensive excision, such as in the case of necrotizing fasciitis.

Contraindications

There are not many contraindications to wound grafts except for a few, such as infected wound bed and under-resuscitated patient.

Preparation

Following are some necessary prerequisites needed to carry out the procedure of wound grafting successfully:

• Watson knife, Goulian blade
• Scalpel 
• Electrocautery 
• Dermatome 
• Mineral oil 
• Skin mesher
• Suture or staples

An appropriate team includes a well-trained surgeon, an anesthesiologist, a scrub tech, and a scrub nurse.

Preparation of the wound bed is essential to a successful procedure. Early excision and debridement to healthy tissue are vital to ensuring that the graft will heal. The standard of care for successful grafting is a 95% graft take. Removing eschar and necrotic tissue in a timely manner will lower the risk of developing a wound infection. This is essential to preventing the loss of the graft. Early excision has also been proven to decrease the number of contractures, scarring, skin tightness, and patients often are rehabilitated faster.[10][11]

The eschar is removed in layers until healthy tissue is identified by diffuse punctate bleeding with a Watson knife or Goulian blade. This is known as tangential excision. Fascial excision allows for faster resection and provides a plane that is ready for grafting but can lead to subpar cosmetic results. Wounds over joints need early excision and grafting to help prevent excessive contracture.[12][1][13]

Before placing the graft, all granulation tissue should be excised as it can have a significant bacterial burden and will prevent adherence of the graft. Skin margins should be freshened to expose healthy dermis. Hemostasis must be ensured to prevent the formation of a hematoma, failing the graft.[1]

Technique or Treatment

Full-thickness skin grafts include both the epidermis and the dermis. The selection of the donor site is carefully considered for optimal cosmetic outcome and control of discomfort. Cosmetic outcome is based on desired pigmentation, texture, and skin thickness.[2] These skin grafts are used to minimize the degree of contracture across joints as well as on the face and fingers.[14][2]

Full-thickness grafts are chosen from the flank, groin, hypothenar eminence, pre- and post-auricular areas, or the forearm.

• The skin is shaved, and the tumescent is injected into the tissue below the intended donor site.
• The skin is then gently harvested using a scalpel, customizing the shape to that of the area to be grafted. Sharp dissection is preferred as electrocautery can damage the donor graft very easily.
• Some of the subcutaneous tissue is removed with the graft, it is then taken to the back table and “defatted” to remove the excess tissue. The donor site is then closed primarily.
• When placing the full-thickness skin graft, it is sutured along the edges using rapidly dissolving sutures. Many surgeons use quilting sutures to help hold the graft in place, preventing both shear and empty space in which a hematoma or seroma could develop. Larger grafts (>3 cm diameter - Stephenson) risk failure because the surface area will be too large for adequate imbibition.

Split thickness skin grafts (STSGs) are the most common type of wound graft placed. They are ideal because smaller amounts of harvested skin can cover a larger area. The dermis and epidermis from the donor site also heal quickly (10-14 days), and that location can be used as a donor site again if necessary. The ideal donor site is the anterolateral thigh because it is easily accessed on the supine patient, it is easy to use the dermatome in this location, and the dressings required are in an easily accessible location.[15]

STSGs are generally meshed to allow for increased coverage when limited donor skin is available. This is useful for decreasing the amount of skin harvest, but the interstices also allow for the egress of serum and blood buildup, minimizing the risk of losing the graft because it will maintain contact with the underlying wound. The most common ratios utilized in meshing are 1:1 to 3:1. Increasing this to 4:1 or higher can be done but there is an increased risk of the graft not taking because the distance between the interstices is too large for the skin to heal between them.[16][14]. The orientation of the graft, when placed on the body surface to be covered, can affect the amount of coverage available based on the meshing pattern.[17]

Sheet grafts are STSGs that are unmeshed. The largest disadvantage of STSGs is the cosmetic outcome. The meshing is scarred into place at the wound site. They also have increased rates of contracture during healing. Sheet grafts are used in areas greater than 3 cm on the face and hands to reduce the contracture and improve cosmetic outcomes. They are also used in areas that are more commonly exposed, such as the forearms and legs, if possible. The risks of seroma and hematoma buildup resulting in loss of the graft are similar to those associated with full-thickness grafts, so they must be monitored closely.[1]

• Infiltrate subcutaneous tissue with tumescent infiltrate.
• Ensure the dermatome is at the correct height for the desired thickness. This can be as thin as 1/1000 of an inch, but the most common thickness utilized is between 8/1000 and 12/1000 of an inch. This can be easily checked with a #10 scalpel blade. If the blade falls into the space between the dermatome and the dermatome blade, the harvested skin will likely be too thick. The scalpel blade should fit into space easily and then become snug as the scalpel blade thickens. It is essential that appropriate thickness is checked every time, even if the settings are the same.
• The area to be harvested is covered in mineral oil to decrease resistance. Tension is applied to the donor site to make it as even and flat as possible. The dermatome is introduced at a 45-degree angle and advanced while placing downward pressure. It is essential to place appropriate pressure to keep the dermatome in the dermis. Too much pressure will result in a skin graft that is too thick, and the donor site will need more time to heal or may even require primary closure if a full-thickness graft is taken. Too little pressure will result in a skin graft that is too thin, uneven, and irregular. Once the desired length is obtained, the dermatome is lifted off the surface, generally amputating the graft from the adjacent skin left in place. If it does not amputate, it can be severed with a scalpel. The donor site is then covered with a 1:1000 epinephrine and a normal saline pad to allow for hemostasis.
• If the graft is to be meshed, it is taken to the back table where it is placed in the mesher at the desired ratio.
• Once meshed, the STSG is placed on the wound with the dermis side contacting the wound bed. It is then either sutured or stapled into place to reduce shearing and improve contact with the wound. It can also be secured with fibrin sealants, but these are often used in combination with staples and sutures.

Dressings

• Graft site
• The graft must be immobilized to prevent shear injury to the healing areas. Shearing of the graft results in failure of neovascularization and leads to graft death. This is especially important with full-thickness grafts and sheet grafts.
• Negative pressure wound therapy (NPWT) is an ideal dressing choice because it pulls all excessive fluid out from under the graft while keeping it in place. This minimizes risks of shearing. This is the preferred dressing method to protect the skin graft of many surgeons and has been demonstrated to be superior to bolstered dressings.[18][19]
• If NPWT is not available, bolstered dressings can be placed and tied or sutured into place to ensure that the underlying graft does not move. The bolster is generally an absorbent gauze to assist with the egress of exudate that will occur.

• Donor site
• Donor site dressing options are numerous and often surgeon dependent. A commonly used dressing is vaseline gauze. It is important to use nonadherent dressings that will not pull off the healing skin when changed. It is usually changed around postoperative day 5.

Complications

Failure of the graft can occur due to fluid build-up under the graft, infection, shearing, excessive tension, or poor vascularity of the wound bed. These complications can generally be avoided if appropriate wound bed preparation is performed along with meticulous hemostasis. The graft is further protected by securing it in place and by the dressings. Care must be taken along each step of the way to provide the graft with the best chance of survival.

Long term contracture and scarring can result. Contracture over joints can be improved by early mobilization, but this must be carefully balanced to avoid damage to the underlying grafts.[13]

Clinical Significance

Skin grafts can be a life-altering procedure for patients with large wounds that would otherwise be unable to heal. Cosmesis is often determined by timely wound debridement and treatment, often at specialized centers, if the wounds are large enough. It is essential that all teams work together, so that wound debridement and grafting occur in a timely manner so that patients have optimal outcomes. Patients with extensive injuries or burns that do not have sufficient skin available for grafting may be appropriate candidates for skin substitutes. Reestablishing skin continuity is essential to preventing infections and reduce insensible fluid losses, as well as provide patients with an increased quality of life.

Enhancing Healthcare Team Outcomes

Communication between the wound care specialist, the surgeon, and the care team is necessary to ensure that a proper wound bed is prepared and that no infection exists in the wound bed. The care team is essential to this process because they change bandages daily and see the wounds. They are also responsible for the care of the patient after the graft when it is most fragile and must be protected.