What is a failed or compromised skin graft?
Skin grafting, including skin substitutes, is a procedure to reconstruct a skin defect that cannot fill in on its own or in which primary closure cannot be done. This is important, as the skin offers protection from the elements and infectious organisms, as well as temperature control and other functions.
There are several layers of skin, the uppermost having the most keratin. The top layer, the epidermis, is made to experience the elements and designed for loss and regeneration.
- Split-thickness graft: is composed of the top layer of skin, the epidermis, and some of the next layer, the dermis. Because some dermis is left, the donor area can heal. This is preferred for large areas and has the advantage of allowing harvesting. The success “take” rate for split-thickness grafts is 95%.
- Full-thickness graft: has all skin layers. This also has a success rate of 95%.
Autograft refers to transfer of skin (split-thickness or full-thickness) from one site to another on the same person. This eliminates immunological rejection issues. Capillaries from the site upon which the autograft is grafted restore blood supply over the first 3 days and full circulation is expected in 4-7 days. A split thickness donation leaves dermis behind, allowing it to heal, but the transplanted skin is delicate and can contract (contracture). A full thickness donation leaves an additional defect at the site from which the graft was procured; this is closed by approximating the edges of the new defect. In spite of this, a full thickness donation offers a better result with its smoothness and flexibility and better protection because of its thickness, but fails more frequently due to fluid accumulation and impaired drainage.
Allografts are harvested from others, making the graft genetically different from the recipient. Included in the allograft category is human amniotic membrane which contains growth factors that promote healing. Allografts are used primarily in burn patients. The immune reaction to allografts is diminished by “decellularizing” the tissue of its epidermal and cellular components.
Xenografts use porcine tissue, which constitutes grafting from an unrelated species. It is used for temporary skin coverage of expansive areas, such as occurs in burns. They are always available, but they are not as successful as allografts.
When a wound is not well vascularized, a flap is used to improve the chances of success. A flap, a section of pivoted tissue from an well-vascularized adjacent area, enhances neovascularization and also allows the cosmetic advantage of healing with similar pigmentation.
Biosynthetic material can be temporarily used to protect clean wounds from drying (desiccation). They generally separate once reepithelialization has occurred.
The thinner the graft, the more likely it will contract. Choice of what type of graft is used must strike a balance between contracture of thin grafts vs. the increased vascularity a thicker graft requires.