Skin Grafting for Burns and Trauma

The initial history of skin grafting goes back thousands of years, but most recent scientific evaluation has been done as of the 1800s. A skin graft basically consists of a epidermis and variable amounts of dermis or all of the dermis. This can be then harvested, fully devascularized, and placed on a recipient wound bed, where it will take as new skin. The fact that this tissue is completely devascularized makes it a true graft. True grafts require revascularization within the bed where they are placed.^[1,2]

There are different types of skin grafts. Split-thickness skin grafts can be very thin, between 6 and 10 microns, medium thickness (10 to 16 microns), or thick (greater than 16 microns). This thickness can be modified based on the dermatome that is used to harvest the split-thickness skin graft. When the entire dermis is used, this is considered a full-thickness skin graft, and the donor site will require primary closure.^[2,3]

Skin graft “take” happens over well-defined stages. Initially, the skin graft survives by plasmatic imbibition where the skin receives its fluid and nutrients from the serum of the underlying wound bed. Capillaries then line up; this is a process called inosculation. This is then followed by revascularization.^[1]

The most important consideration for skin graft “take” is that the wound bed of the recipient site has to be vascularized enough to support this revascularization process. Skin grafts often will not take on bone or exposed devascularized tendon. Preparation of the wound bed after an acute situation with open wounds is paramount to the success of the skin graft. Skin grafts will not take if the recipient wound bed is not vascularized enough, as in bones and tendon, if there is excessive bleeding or hematoma between the wound bed surface and the graft, or if there is a high degree of bacterial contamination.^[4]

Therefore, appropriate debridement and hemostasis is paramount to getting the skin graft to work well. Thinner skin grafts will take better on a contaminated wound bed than thick skin grafts. However, there will be more secondary contraction. If the goal is to get wound closure, thinner skin grafts are more functional. If the goal is better aesthetic outcome and less secondary contracture, then thicker skin grafts are recommended.

Different types of dermatomes can be used for harvesting the skin. The most commonly used dermatome is the Zimmer dermatome, which can be electric or air-driven. These dermatomes can get skin grafts of various thicknesses very well calibrated.^[1] The dermatome requires a large blade that needs to be replaced. Calibration of different dermatomes can be accomplished with the assistance of a scalpel blade. At 10 microns, the shiny part of a fresh 10 blade will disappear but without the blade falling through the shim. Different widths can also be calibrated, anywhere between 1 to 4 inches in width. The donor sites are often injected with clysis in order to make harvesting more even and easier.

The skin that is harvested can then be meshed in a fishnet-type pattern of different thicknesses so that the skin graft can be placed over a larger wound area. This also helps with better drainage, preventing a hematoma from forming. However this leads to more secondary contraction and a less favorable aesthetic appearance.

The area of the skin graft then needs to be immobilized on the wound bed. This is often done with a stent or bolster. This prevents shear forces from disrupting the revascularization process. Usually, the stent is sewn into place with cotton and a nonstick dressing. The area should have edema control, such as extremity elevation or vacuum-assisted closure (VAC) wound dressing. The VAC can act as a stent, the key being keeping a nonstick dressing between the graft and the sponge of the VAC.

Not getting appropriate hemostasis will lead to graft loss. Not doing enough debridement with high bacterial counts over 10 to the fifth will lead to graft loss as well.^[5] Any type of shear force, especially in the situation of edema, will disrupt the neovascularization process and lead to skin graft loss. The stent can be left on in the setting of a contaminated wound for as much as seven days but often requires topical antimicrobials, such as Sulfamylon slurry or silver nitrate and potentially systemic antibiotics.

The donor site of a split-thickness skin graft is very painful and may require different management of care. If it is a large donor site (larger than 100cm²), we recommend using Xeroform dressings and allowing it to dry out. Smaller donor sites can be dressed with an occlusive dressing, which will be much less painful and has the potential to re-epithelialize faster. The vast majority of the time for anything over 1% TBSA donor site, we will use just the Xeroform and allow it to dry out and heal secondarily. The donor site heals faster for thinner grafts, as fast as seven days for a harvesting of a 10 micron thickness skin graft. These areas that are taken very thin can be reharvested as early as seven days later but this usually takes longer in most clinical scenarios, up to a month. If the donor site is very deep, there is a higher chance for hypertrophic scar formation and the inability to harvest that site again.

If donor sites get significantly contaminated, a partial-thickness injury can become full-thickness injury. If the donor site is more likely to be contaminated, using topical antimicrobials such as Sulfamylon or silver nitrate may be required to avoid secondary infection.

There are special situations that require certain treatment. The calvarium of exposed skull may require burring of the calvarium to get good granulation tissue. This can be used in conjunction with VAC dressing management to try to get the wound bed to granulate faster in order for it to accept a skin graft. If the exposed bone is already too thin (such as an electrical burn) or the diploe is too hard to get to, it may require a scalp flap as opposed to a skin graft. If the scalp flap is rotated, the donor area can be grafted on the pericranium. Be careful not to tie down the stent too tight as it could cause ischemia to the pericranium.

Secondary management of scar contractures found in large burns may require releases to the scar and then placement of the skin graft.^[6,7] Deep facial burns may be associated with corneal exposure. This situation requires release of the surrounding constricting scar and a placement of a thick skin graft to preserve eyelid function and preserve vision and globe moisture. Deep neck burns may require release in order to make repeat surgery safer for intubation. In general, wait on nonurgent secondary scar management release and grafting to allow the scar to mature first. The releases are much more effective on mature scars and avoid grafting onto fascia and causing deformities that would be difficult to correct.

Old, large, nonexcised wounds with significant debris require staged debridements followed by topical antimicrobials in order to get the wound to have a lower bacterial count and then survive the grafting. Grafting is most often accomplished with the assistance of a topical antimicrobial such as Sulfamylon slurry. In the pediatric age group, the skin is much thinner, and thinner skin grafts have to be considered. This is also the case in older-age patients with also very thin, fragile skin. In the older age groups, occasionally the skin graft is meshed, and excess part of that skin graft after meshing is placed back on the donor site in order to allow that to heal faster.

There are certain situations where xenografts or allografts can be used, especially in larger burns. Allografts allow the function of the skin to return, hopefully dropping the bacterial count and preparing the area for eventual autografting. This requires a skin bank. In the event that a skin bank is not available, xenografts are used, but these are usually rejected within a week. This, however, can allow for dropping the bacterial count and assisting in stabilizing the patient during the acute process of excisional debridements, preparing the wounds for eventual autografting. In wounds with small areas of exposed tendon when a flap is not necessarily available, skin substitutes such as Integra® or NovoSorb® BTM (Biodegradable Temporizing Matrix) can be considered.^[8]

This can occasionally bridge over small areas of exposed tendon and bone. This then requires secondary grafting with a thin split-thickness skin graft taken at approximately 6 microns in thickness. Large areas of exposed bone or tendon will not take skin graft or integra or other skin substitutes and will require flap surgery.