You may recall that a skin graft involves taking a piece of skin from one area of the body and using that skin to cover the original wound (link to blog post Oct 4). The graft relies on the blood supply of the wound bed to get nutrition. During the first few days after the grafted skin is placed, the graft will “drink” from the wound bed, hence the term imbibition. By day 3 to 5, the graft has usually created adhesions to the wound bed. This adherence is critical to graft survival. Necessary blood supply is initiated by capillaries starting to grow into the graft (inosculation). Finally, larger blood vessel revascularize the graft.
A thick graft will have a lower chance of survival than a thin graft, since a greater amount of skin must be nourished in the former. For those reasons, thinner (split thickness) skin grafts are often used when there is concern over blood supply in the wound. This may be the case for lower extremity wounds or where there has been prior scarring. Unfortunately, those thinner (split thickness) skin grafts have worse cosmetic outcomes and less sensation than thicker (full thickness) skin grafts.
Why would anyone choose to perform a skin graft? Why not just close the original wound and avoid making another wound?
There are four common scenarios in which a graft is commonly used after tumor removal:
- Tension will distort the area and lead to poor aesthetic outcome. Placing these areas (also colled free margins) under tension will distort them. This might be the case on the lower nose of near the eyelid.
- The margins of a removed tumor (see blog post on Mohs and margins) are questionably clear or the tumor was very high risk. The worry here is recurrence and a graft will allow for easy surveillance of the wound area for tumor recurrence. Since even a full thickness graft is much thinner than a typical skin flap, a tumor recurrence might be caught earlier in a grfated wound than if a flap were used. A split thickness graft may be a good choice here, since it has a better survival rate and is thinner to facilitate tumor recurrence surveillance.
- The skin will not stretch enough to allow the skin edges to meet. This is classic for scalp and lower extremity areas such as shin. The skin in these areas often shows limited laxity. Intraoperative skin relaxation is a great option here to help avoid a graft. Using a SUTUREGARD ISR device for 30 minutes on the scalp results in wounds that are under 65% less tension. This often allows a linear closure instead of a graft. In the context of Mohs surgery (link to Mohs blog post), the patient is waiting for tissue processing, so it is a great time to get some skin relaxation during that waiting period.
- The tension needed to get the wound together is greater than the strength of the skin – leading to skin tearing. This is also a common occurrence on shin, where skin has limited laxity and strength. This skin rips easily when sutured under tension. In these cases, a graft can be avoided using the HEMIGARD adhesive retention device. This device helps prevent skin ripping when suturing, allowing would closure under tension in delicate or fragile skin.
- A combination of the above. For example, burned skin can exhibit both poor stretch due to scarring and is very fragile.
What happens after the graft? There are two major schools of thought on graft wound care. In one camp, a bolster is sewn over the grafted skin. This bolster can be made from a variety of dressing materials and serves to press the graft against the wound bed. Recall that a skin graft relies on blood supply from the wound bed. If the grafted skin were to be separated from the wound bed by a collection of blood (hematoma) or other fluid (seroma), then the graft will die. The bolster is done with the hope of helping to prevent a separation and also help prevent accidental damage of the graft during the initial healing.
Others choose not to bolster the grafts. This option saves intraoperative time and leads to easier wound care of the graft. Many surgeons will make the decision to bolster on a case-by-case basis.