Split-Thickness Skin Grafts

Excerpt

Skin grafting is the transfer of cutaneous tissue from one portion of the body to another, often used to cover large wounds. The rationale of skin grafts is to take skin from a donor site that will heal and transfer the skin to an area of need. After incorporation, skin grafts provide wounds with protection from the environment, pathogens, temperature, and excessive water loss like normal skin.

A split-thickness skin graft (STSG), by definition, refers to a graft that contains the epidermis and a portion of the dermis, which is in contrast to a full-thickness skin graft (FTSG) which consists of the epidermis and entire dermis. Unlike flaps, skin grafts do not have their own blood supply, so they must rely on a well-vascularized wound bed for graft in-growth. Split-thickness skin grafts are obtainable from multiple sources (autograft, homograft, allograft, or xenograft), multiple anatomical locations, and in various thicknesses. Most commonly, STSG autografts are taken from the lateral thigh, as well as trunk, as these sites are both aesthetically hidden, as well as easy to harvest from due to their broad surfaces. Split-thickness skin grafts classify according to their thickness into thin STSGs (0.15 to 0.3mm), intermediate STSGs (0.3 to 0.45mm), and thick STSGs (0.45 to 0.6mm). Because split-thickness skin graft donor sites retain portions of the dermis, including dermal appendages, the donor site can regrow new skin in 2 to 3 weeks. Thus, donor sites can be used more than once after appropriate healing has taken place, which makes STSGs versatile in burn surgery and large wounds where there are limited donor sites.

The advantages and disadvantages of STSGs are best highlighted by comparison with FTSGs. Considerations of proper skin graft selection should include graft take, contracture of skin graft, donor site morbidity, aesthetic match, and durability.

1. Graft Take: The thicker a skin graft, the more metabolically active it is, and the worse is it's nutrient diffusion. FTSGs and thick STSG's require more robust recipient wound beds than thin STSGs. Thick grafts should be avoided in unhealthy wound beds such as chronic ulcers.

2. Contracture: All skin grafts undergo primary and secondary contractures. Primary contracture is the immediate reduction in the size of skin graft after it has been harvested, caused by passive recoil of elastin fibers in the dermis. As FTSGs have a greater amount of dermis, primary contracture is more significant in FTSG than STSG. Secondary contracture is the shrinkage of the skin graft in the wound bed over time, caused by myofibroblasts. Secondary contracture is greater for STSGs than FTSGs, as the additional dermis in FTSGs is resistant to the pull of myofibroblasts. Clinically, STSG placement should not be in aesthetically sensitive areas that could become deformed with contractures such as around the eyelids, face, and mouth.

3. Donor Site Morbidity: The multipotent stem cells responsible for STSG donor site reepithelialization primarily reside in the hair follicles. By preserving portions of the dermis and thereby hair follicles, STSG donor sites regrow new skin and are reusable. Thin STSGs have the least donor site morbidity and regrow new skin the fastest. Full-thickness skin grafts involve excision of the entire thickness of skin, and thus adnexal structures, necessitating primary closure.

4. Aesthetic Match: Skin grafts should ideally match the recipient bed in color, texture, and overall appearance. Full-thickness skin grafts commonly provide an appropriate color match, whereas STSGs are more likely to be hypo/hyperpigmented. Additionally, the meshing of STSGs significantly alters the aesthetics of STSGs.

5. Durability: As the dermis provides strength and viscoelastic properties to the skin, the consideration of dermal thickness is essential for each specific wound. For example, thick STSGs or FTSG are common choices to cover mechanically demanding areas of the body, including the palms, soles, and joints, whereas thin STSGs do not withstand such forces as well.

Disadvantages of STSGs compared to other reconstructive techniques include at times poor resemblance to surrounding recipient site skin (color match and texture if meshed), high susceptibility to trauma, poor sensation of the recipient site, need for anesthesia/surgery (compared to secondary intention healing), and prolonged need for wound care of both the donor and recipient sites (compared to flap closure).