Some wounds are too large to close with stitches alone. In those cases a vet may cover the gap with skin moved from nearby (a flap) or with a piece of skin taken from somewhere else on the body (a graft). Vets use both in dogs and cats, for wounds left after a lump is removed as well as for wounds from injuries [1][3].
If your pet has had a flap or graft, follow your vet’s instructions exactly and go back for every recheck. If you are worried about the wound, call your vet.
What a skin flap is
A flap is a section of skin that the surgeon shifts over a wound while one part of it stays connected to the body, so it keeps a blood supply. In a large study of dogs, removing a lump was by far the most common reason for this kind of surgery [1]. Surgeons try to close the skin without pulling it too tight, because tension, infection, bleeding under the skin and swelling can all cut off blood flow to the flap [1].
There are two main kinds. Some flaps include a named skin artery and vein, which gives them a strong and predictable blood supply. These are called axial pattern flaps. Others rely only on the fine network of small vessels under the skin, called the subdermal plexus [1]. Axial pattern flaps are usually seen as the more reliable choice, but in that study of 85 flaps in 78 dogs the two kinds healed about equally well [1].
What a skin graft is
A free skin graft is a piece of skin cut loose from one place and laid over a wound somewhere else, so it has to pick up a new blood supply from the wound bed. Vets use grafts for large wounds where there is not enough loose skin nearby, for example on the lower legs [2][4]. Degloving is when skin is torn away from the tissue under it. For more on these wounds, see degloving injuries in dogs and cats.
Why the wound bed matters
A graft or flap needs a healthy base to grow onto. Before grafting, vets usually clean the wound, remove dead tissue and wait until a layer of healthy red granulation tissue has formed and there are no signs of infection [2][3]. Granulation tissue is the new, moist tissue that fills a healing wound. Infection at the graft site and movement of the graft are the main things that make a graft fail [2]. Cats build granulation tissue more slowly and in smaller amounts than dogs [2], so their wounds may need longer before surgery. This is one reason your vet may treat a wound for a while before a flap or graft.
Vacuum wound therapy
Negative pressure wound therapy, often called vacuum therapy, uses a sealed dressing and gentle suction on the wound. In dogs and cats it is one of the methods used to help large wounds on the lower legs heal, and it can help skin grafts take there. It needs special equipment, and the aftercare is more demanding [4]. Your vet will decide whether this suits your pet’s wound.
After surgery
Some swelling, bruising and discharge can show up after flap surgery. In the dog study, the most common problem was the wound edges opening partly, and dead skin (necrosis) on the flap was the problem most closely tied to that. Swelling and discharge were linked to it too [1]. Lack of blood supply is the usual cause of dead skin on a flap or graft [3]. Most of these breakdowns were partial, and only a few needed another operation to remove dead tissue [1]. Wounds on the lower legs broke down most often [1]. Only your vet can judge whether a flap or graft is healing well.
At home, as directed by a vet
- do not touch, remove or change a bandage or dressing unless your vet says so;
- follow your vet’s instructions for the wound exactly, including any limits on movement;
- do not give your pet human or leftover medicines unless your vet says so;
- go back for every recheck your vet books.
When to see your vet
See your vet if your pet has:
- skin on a flap or graft that turns dark or black [1][3];
- swelling, discharge or wound edges that start to come apart [1];
- anything about the wound, flap, graft or dressing that you are unsure about.
The bottom line
Skin flaps and grafts are ways a vet can cover a large wound with skin, and vacuum wound therapy is one way to help a wound close. They need a clean, healthy wound bed, and your vet decides which, if any, suits your pet.
This article is for general information only and does not replace advice from your veterinarian. If you have any question about your pet’s wound, flap or graft, ask your vet.
Sources
- Boonwittaya N, Noonoi P, Prawadwin S, Thengchaisri N. Retrospective comparison of axial pattern and subdermal plexus flaps in canine reconstructive surgery: Surgical outcomes, complications, and factors associated with wound dehiscence. Veterinary World. 2026;19(6):2393-2405. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC13392620/
- Oros NV, Repciuc C, Ober C, Mihai M, Oana LI. Combined Oxygen-Ozone Therapy for Mesh Skin Graft in a Cat with a Hindlimb Extensive Wound. Animals (Basel). 2023;13(3):513. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC9913348/
- Oros NV, Repciuc CC, Bel LV, Melega I, Pertea AN, Oana LI. Preoperative and Postoperative Ozone Therapy in Cats Presenting Extensive Wounds Treated by Reconstructive Surgery Methods: A Short Case Series. Veterinary Sciences. 2025;12(8):786. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12390682/
- Makar JG, Baltzer WI, et al. Autologous, free omentum grafts for large, open, distal limb wounds in dogs: Technique and outcome in 10 dogs. Veterinary Surgery. Published online July 9, 2025. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12907535/