Skin grafts

Skin grafts are harvested from a donor site and transferred to a recipient site on which they must survive, a process known as take. All skin grafts initially adhere to the recipient bed by the formation of fibrin. Oxygen and nutrients diffuse through by a process known as plasmatic imbibition to keep the graft alive. New blood vessels then grow from the recipient site and link up with dermal capillaries to re-establish a blood supply, a process known as inosculation. Thin skin grafts are more likely to survive by imbibition and will revascularise readily and are therefore more likely to take than thicker grafts. Thicker grafts, however, will have more dermis, more sebaceous glands, greater structural integrity and a lesser tendency to contract.

Partial-thickness skin grafts

Partial-thickness skin grafts consist of epidermis and a variable thickness of dermis. There remains some dermis on the donor site that heals by epithelialisation from the cut ends of hair follicles and sweat glands in a manner similar to the healing of a graze or a superficial burn. The thigh, is most frequently used as a donor site, but almost anywhere else can be used. Grafts are harvested using a skin graft knife or a power dermatome. These consist of a blade and a guard that can be adjusted to determine the thickness of the graft. Hand knives require practice to use and the graft obtained remains dependent on the tension in the donor site skin, the pressure that the surgeon applies, the speed and length of the strokes used and the angle of application of the blade (Fig. 13.1). With air- or electric-powered dermatomes these factors become less important and more consistent results can be obtained. Partial-thickness grafts are used to resurface relatively large areas of skin defect and are particularly useful in burns (Fig. 13.2a and b).

Full-thickness grafts

Full-thickness grafts consist of epidermis and all of the der­mis; the donor site will not epithelialise and must be closed, usually directly. Suitable donor sites are postauricular, supra­clavicular and groin. Full-thickness grafts are most commonly used in repairing defects on the face (Fig. 13.3a—c). Grafts taken from above the clavicles retain the ability to blush and can provide a very good colour match for facial skin, whereas grafts from below the clavicles will tend to look pale. Full-thickness grafts are harvested using a scalpel and forceps, dissecting at a level just below the dermis. As they are thick special care is needed to ensure good apposition to a well-vascularised bed to ensure good take.

Composite grafts

Composite grafts consist of skin and some underlying tissue such as fat and cartilage. Again, donor sites must be closed directly. Composite grafts carry the highest risk of failure yet potentially can repair complex defects. These grafts ‘have to be carefully designed to be as thin as possible and have a large area of inset in order to survive. Their maximum thickness can only be a few millimetres; it is futile to replace larger portions of composite tissues — for larger defects flap repairs are needed. Portions of ear, skin and cartilage can be used to reconstruct nasal defects. Amputated fingertip pulp in children will sometimes survive if carefully replaced as a composite graft.

Other tissues

Other tissues can also be transferred as grafts. Cartilage grafts are commonly used in nasal and ear reconstruction. Cartilage is an avascular tissue; survival of transplanted chondrocytes depends entirely on diffusion of nutrients. Bone grafts are widely used for skeletal reconstruction. Nerve, tendon, vein, fascia and cornea are also all in common use.

Technical aspects

Graft take is only possible at well-vascularised recipient sites. Grafts will not take on bare bone, bare tendon or cartilage, but can survive on periosteum, paratenon and perichondrium. The graft must remain adherent to the bed until it revascularises; shearing forces must be eliminated. Meti­culous care with suturing and dressings is essential. Where grafts are applied over mobile areas appropriate splintage must be used. Limbs that have been grafted should be elevated to reduce venous pressure during the process of revascularisation. Haemostasis at the recipient site must be good to prevent bleeding beneath the graft resulting in its elevation by clot and failure of take. Skin grafts can be stored in a refrigerator at 40C for 2 weeks for delayed application. Grafts take well on granulation tissue, but excessive conta­mination with bacteria will prevent take. Streptococci at levels above 105 microorganisms per gram of tissue will result in graft loss. Preparation of the bed with dressings may help; it may be necessary to excise the granulation tissue.