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
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.