Skin graft
A skin transplant is a transplantation of skin to cover skin defects such as burn accidents , chemical burns , chronic ulcers or wounds. The sampling point is typically a healthy area of skin on the thigh or another place normally covered by clothing; animals usually have enough mobile skin on the chest. An infection-free, granulating wound is a prerequisite for the success of the split-thickness skin graft .
to form
A distinction is made between the free skin grafting and the swiveling flap technique, as well as the pedicled remote grafting within the framework of flap surgery .
The fastest possible connection with the blood vessel system of the neighboring healthy tissue or the growth of new vessels into the transplant is critical for the growth of a free skin graft, since otherwise the piece of skin will die off ( necrosis ). The growth is safest if the blood vessel system of the transplant is vascular surgically connected directly to the vessels of the neighboring tissue. With the swivel flap technique, the existing blood supply is maintained and the piece of skin is swiveled over the wound.
In principle, either full skin or split skin can be transplanted with free skin grafting . With full skin, the entire epidermis (upper skin) and dermis (dermis) is transferred, it is important that the subcutaneous tissue is removed as far as possible. With the split skin technique, on the other hand, only parts of the dermis are transferred. With a dermatome (hand dermatome , compressed air dermatome or electrodermatome) or a scalpel , a 0.2 to 0.6 mm thick flap is removed and used to cover the defect. In the case of split flaps, the hair follicles are usually damaged, so that the transplanted piece of skin shows sparse or no hair growth at all, which is of cosmetic importance in veterinary medicine in particular.
Researchers at the University of Zurich have developed a method in which an artificial full thickness skin ( artificial skin can be produced) and transplanted. A piece of the patient's skin is divided into layers and broken down into individual cell types with the help of enzymes; on collagen , a new, complete skin grows out of it, which can be transplanted. This procedure is to be used in 2013 at the Children's Hospital Zurich , in Berlin and in Amsterdam on children with severe burns.
Mesh Transplant
If larger defects are covered, the graft recovered can with the technique of mesh transplantation ( mesh graft to the method for producing), similar expanded metal , are provided on a knife roll with a diamond-shaped pattern, and so by the possible extension of up to three times as large area cover. The incisions go through the entire thickness of the graft and can also be made with a scalpel. This procedure also has the advantage that wound exudate can drain through the openings in the graft.
Meek transplant
If even larger areas need to be covered (e.g. for severely burned people), the Meek transplant technique from 1958 (named after C. P. Meek, who first described it) is used. Here, the split skin that has been removed is stretched onto cork sheets and then cut into squares around 2 millimeters by 2 millimeters with the help of rotating blades. These are applied to special one-time stretchable textiles and then pulled apart up to a ratio of maximum 1: 6. These textile pads are then applied to the wound and anchored.
requirements
The receiving bed must consist of fresh, uninfected granulation tissue . Older granulation tissue needs to be refreshed. Bleeding should be stopped as completely as possible, since accumulations of fluid between the wound bed and the transplant prevent it from growing. Exposed bones, cartilage, tendons, and nerves prevent the graft from growing.
Healing processes
The first connection between the receiving bed and the skin graft is made by exuding fibrin . A bacterial infection leads to the dissolution of the fibrin and thus to the detachment of the transplant. Secondly, a more intimate connection is guaranteed within about ten days by newly formed connective tissue .
Rapid restoration of blood flow is necessary for the skin graft to survive. If the vascular network of the transplant is connected directly to the blood vessels of the neighboring tissue via microsurgery, this is guaranteed quickly. If this does not take place, the supply of the transplant is initially ensured by serum-like fluid, which penetrates into the vessels of the transplant via capillary forces (plasmatic imbibition ). The absorbed fluid initially leads to edema , which experiences its maximum for two to three days.
If a microsurgical connection of the vascular networks is not possible, there are two ways to connect the vascular networks. On the one hand, anastomoses can form spontaneously , through which the flow is initially in a disordered manner, and from about 7 days onwards show an orderly blood flow. On the other hand, new blood vessels can sprout after about 2 to 3 days ( angiogenesis ). New lymph vessels form after about 4 to 5 days. With these processes, the edema also recedes. The color of the transplant changes according to the quality of the vascular supply from originally pale to slightly reddish after 3 to 4 days, to red after about a week and reaches the normal skin color after 14 days. Hair regrowth begins around 2 to 3 weeks after the transplant.
In principle, the transplanted piece of skin should be immobilized for at least three weeks, as movements prevent it from growing and connecting to the blood vessel system.
Follow-up
After initially covering the extraction point with vaseline dressings or the like, the infection-free wound can be air-dried and treated like a deep abrasion. The complete cutting out of the removal points that are not too wide and the subsequent seam has also proven successful. As after other operations, the healed scar is narrow and mostly barely visible. In the case of large removal points, a transparent film can also be used, which is removed gradually over the regrown skin.
At the graft site, the bandages are often used to apply slight pressure in order to ensure that the granulation tissue can grow into the vessels. At the same time, the wound is immobilized for a few days to avoid disruptive movements between the graft and the wound bed. For a few years now, vacuum therapy has also been used to improve healing by pressing the transplant against the recipient site and promoting granulation.
Complications
If the transplant is rejected, infection is often the cause. Healing disorders also arise with poor local blood circulation and when the split-thickness skin graft is not applied tension-free and therefore does not lie sufficiently on the wound bed.
See also
literature
- Cheryl S. Hedlund: Surgery of the integumentary system . In: Theresa Welch Fossum (Ed.): Small Animal Surgery . 2nd Edition. Mosby, 2002, pp. 134-228.
Individual evidence
- ↑ New skin for children. In: UZH News. University of Zurich , March 8, 2013, accessed March 8, 2013 .
