The skin is the largest organ of the human body and has many essential functions. It creates a protective barrier against pathogens, indoor and outdoor environment. It acts as a water-resistant barrier so essential nutrients are not removed from the body. It provides a dry and semi-permeable barrier to fluid loss. Langerhan cells in the skin are part of the adaptive immune system. The skin contains a number of nerve endings that respond to heat, cold, vibration, pressure, touch, and pain as they play an important role in sensation. Thermoregulation is another essential function of the skin and, finally, the skin also plays a vital role in vitamin D synthesis. For all the reasons stated, it is imperative to protect the skin covering in humans.
Skin grafts are taken from the donor area and transferred to a remote recipient area (bed) without carrying their own blood supply. The graft rests on new blood vessels from the recipient zone bed to be created (angiogenesis). Full thickness skin grafts consist of the entire epidermis and dermis. These grafts are a simple and reliable method of covering skin imperfections in cases where primary closure or secondary intention healing is not possible. Full-thickness skin grafts are often used to reveal smaller imperfections because of their limited size. They are invaluable for reconstructing imperfections where good cosmetic results or a durable skin cover are required. Common areas include defects on the face, scalp, and hand, usually following excision of skin lesions. A suitable well-vascular bed is required for full thickness skin graft harvesting. ‘Pick up’ is the process that results in reattachment and revascularization of the skin graft.
Skin Grafting Mechanisms
There are 3 predictable stages of skin graft harvesting:
Initially, skin grafts passively absorb nutrients from the wound bed by diffusion. The imbibition prevents the graft from drying out and keeps the graft vessels open. This allows the graft to survive the post-graft ischemic period, which is an indefinite period that varies according to the wound bed. This can be up to 24 hours for a graft placed in an already proliferative bed, and up to 48 hours for a graft covering a new wound.
When a graft is placed in a poorly vascularized bed, it can tolerate an ischemic interval. Thick full thickness skin grafts can tolerate ischemia for up to 3 days, while thin full thickness skin grafts survive for up to 5 days. Split-thickness grafts receive well even after 4 days of ischemia. Grafts can add up to 40% to their pre-graft weight through the movement of fluid from the recipient bed to the graft and therefore appear fuller during this time.
Vaccination and capillary growth
On day 3, a thin vascular network is established in the fibrin layer between the recipient bed capillary buds coming from the graft and the recipient bed, and the graft veins on the underside of the dermis are aligned to create open channels. Blood flow is achieved and the skin graft turns pink. The proliferation of fibroblasts and the accumulation of collagen to replace fibrin allows the skin graft to adhere to its bed. The bond strength increases rapidly and anchorage can be achieved within 4 days.
On day 5, new blood vessels grow in the graft and the graft is vascularized. As the graft is revascularized, the connection between the graft and host vessels becomes more developed. The newly formed vascular connections continue to differentiate into afferent and efferent vessels. On the fifth or sixth day after the graft notes the presence of lymphatic drainage. The weight of the graft decreases until it reaches its pre-graft weight on the ninth day.
Full Thickness Skin Graft Harvest
Different parts of the body differ greatly in the appearance, color, texture, thickness and vascularity of the skin. All these factors are taken into account when choosing a suitable donor site for a particular defect.
Full thickness skin grafts can be taken from a number of areas of the body with excess skin. While the face is being grafted, the posterior surface of the ear that extends over the neighboring mastoid skin behind the ear provides a perfect donor area in terms of skin color and texture. Another useful area for facial lesions is the preauricular area. The upper eyelid skin is particularly useful when the defect is in another eyelid Supraclavicular skin excised from the lower posterior triangle of the neck gives reasonable color and texture to resurface facial defects. However, this is cosmetically inferior to the skin around the auricle.
Including bending cutaneous-cubital fossa, groin and distal wrist fold are also used as donor sites. The main use of the groin skin is where a long, narrow piece of skin is required, such as managing flexion contractures in the hand. A noticeable scar formation is a realistic possibility when closing the ante-cubital fossa donor sites, but usually causes wound hypertrophy when closed under excessive tension. It is good at providing skin cover for thighs and abdomen, palms. The dermis, which is thicker than these areas, provides a good pad to withstand pressure when used on the sole of the foot. Full thickness skin grafts undergo significant primary contraction after harvest and it is useful to create a template for recipient defect. This shape is then transferred to the donor area and stretched to form an ellipse. The resulting scar extends in the direction of natural skin fold lines (Langer’s lines). The graft is usually collected with a 15 inch blade scalpel between the dermis and subcutaneous fat. Generally, the graft is easier to cut if fluid leaks into the area (1: 200000 adrenaline). Full thickness skin graft does not leave behind any epidermal element in the donor area where resurfacing can be made. Therefore, primary closure of the donor site is required. This is usually achieved using an absorbable suture in a single layer subcuticular suture. Sometimes a double thickness skin graft can be used to cover the donor area.
Graft fat can be removed further as the fat is poorly vascularized and will prevent tight adhesion between the graft dermis and the recipient bed. All yellow oils are cut using a pair of sharp scissors until only the bright white lower surface of the dermis is visible.
A good graft attachment is required to keep the graft still in its bed and to prevent hematoma formation. The graft is fixed to the donor site with stitches with the dermis side down and cut to fit. A non-adhesive layer such as a gelonet wrap is also required to facilitate easy separation of the wrap.
A range of techniques can be used, including bonded wraps, foam backings and quilted stitches. The full thickness skin graft is sewn circumferentially around the wound edges with long cut independent stitches. A laced dressing is applied using a piece of gauze or wool soaked in proflavine and the suture ends are tied to secure the dressing. This helps stabilize the graft and reduces cutting forces. Alternatively, additional pressure and immobilization can be provided by using a foam pad secured with stitches or staples. Quilted stitches applied between the graft and the bed provide immobility and good contact between the graft and the wound bed.
Author: Ozlem Guvenc Agaoglu