Best Practices for Successful Skin Grafts in Horses
Ensuring grafts stay immobile during the critical first week and vascularize over healthy granulation tissue can help them grow successfully at the wound site, said Dean Hendrickson, DVM, MS, Dipl. ACVS, professor of equine surgery at Colorado State University’s College of Veterinary Medicine & Biological Sciences, in Fort Collins.
The faster the healing, the fewer dressing changes and overall expense, he explained during the 2021 American Association of Equine Practitioners’ convention, held Dec. 4-8, in Nashville, Tennessee.
Veterinarians can opt for various grafting techniques that involve removing healthy skin from the patient, usually on the neck under the mane or at the chest, and then carefully preparing it for graft at the wound site.
But regardless of the technique, veterinarians must always remember a graft needs an uninterrupted seven days to set and integrate into the new site.
“If you are someone who absolutely, positively needs to look at wounds on a regular basis, don’t do skin grafting,” he said, addressing his veterinary audience. “There is nothing you are going to do in the first seven days of a skin graft that is going to impact the likelihood of that graft working. But looking at it between the application of the graft and Day 7 just increases the chances of problems. So please leave the dressings on. And this is a real challenge, I think, for some of us.”
Veterinarians must also keep in mind that any movement could cause the graft to die.
For this reason, Hendrickson recommends thick bandaging and often even a splint or a full cast, depending on the graft’s location, to prevent movement.
A successful skin graft also requires optimal granulation tissue at the wound site, with no signs of infection and with the remaining surrounding skin adhering well to the deeper layers, he explained.
“You’re not going to put a skin graft on a dead piece of bone sequestrum of a cannon bone, right? That’s a total waste of time. You have to get good healthy granulation tissue to accomplish that.”
For a better cosmetic look, veterinarians should respect the hair color when choosing the donor site and place the grafts in the same direction of hair growth as the wound site, he added.
Although veterinarians have debated over the years about whether to use full- or partial-thickness donor skin, Hendrickson said he believes full-thickness is best. Some scientists have shown that using only the top half of the skin layer results in more successful vascularization—albeit less cosmetically appealing results. But for Hendrickson, getting good vascularization is entirely possible with full-thickness donor skin, provided veterinarians promote vascularization properly.
Regardless of the vascularization quality, the top part of the graft will die—which can be discouraging, he said. What matters, though, is that the lower part of the graft attaches, vascularizes, and starts growing.
“The surface of the skin graft always dies, because you’ve had too long without any type of nutrient supply,” Hendrickson said. “That’s going to happen on any type of skin graft you do.”
The deeper, healthy part of the skin graft takes about three weeks to begin filling in the wound, he said. With most of the current methods, an uptake of 60-75% of the original graft is considered a success.
In general, veterinarians can perform pinch or punch grafting—either pinching up the donor skin and cutting it out with a scalpel or punching out small circles of donor skin with a biopsy punch—in the field in standing, sedated horses using local anesthesia, said Hendrickson.
For the other techniques, which require more specialized equipment, horses have historically been hospitalized, he said. Those include tunnel grafting (burrowing long tunnels through the donor skin), sheet grafting (cutting out long, thin strips of donor skin), MEEK grafting (using a commercial machine called a MEEK that dices and spreads the donor skin on an adhesive mesh), and pedicle grafting (taking donor skin from just beside the wound site and rotating it around a piece that stays anchored in its original place).
Even so, Hendrickson said he has successfully performed all these procedures in the field after gaining considerable experience.
“Skin grafting isn’t magical, and it’s not something that has to be done in a sterile aseptic field of a tertiary referral center; they can easily be done in a practice setting,” with proper knowledge and experience, he said.
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