Skin
Grafts
The skin consists of two layers; the uppermost layer is
the epidermis and the deeper layer is the dermis. Beneath
the dermis is a layer of fat.
Free skin grafts are of two types;
1. Full Thickness
Skin Grafts consist of the epidermis and the whole thickness
of the dermis.
2. Split -
Skin Grafts consist of the epidermis and a variable quantity
of dermis. Split skin grafts are variously described as
thin, medium or thick depending on the amount of dermis
they contain. The division of split thickness skin grafts
into these sub divisions is somewhat arbitrary and the most
significant differences in skin grafts depends upon whether
the graft is of full thickness or split thickness type.
Differences Between Split Thickness Skin Graft And
Full Thickness Skin Grafts
The surgeon, using a scalpel, cuts full thickness skin grafts.
Simple stitching usually closes the wound from where a full
thickness skin graft is taken from. The wound created when
a whole thickness graft is taken heals in the same way as
a simple incision in the skin and leaves a straight-line
scar.
In contrast, a split thickness skin graft is harvested using
a special instrument (dermatome); the wound created in this
process is allowed to heal under dressings. The wound created
when a split thickness skin graft is taken is like a large
graze. This grazed area heals by re-growth of the epidermal
layer of the skin from epidermal remnants, which are left
behind when the graft was taken. The wounds created when
grafts are harvested are known as the donor sites.
Split thickness skin grafts are used when large wounds need
to be covered. In most situations large potential donor
sites exist for the harvesting of a split thickness skin
grafts. Split thickness skin grafts are typically harvested
from the thighs, buttocks and occasionally the upper limb,
abdomen and back. Full thickness skin grafts are of limited
availability. The ability to harvest full thickness skin
grafts is restricted by the necessity of stitching up the
donor site from which they were taken. Typical full thickness
skin graft donor sites include in front of and behind the
ear, the upper eyelid, the neck and the abdomen.
Split thickness skin grafts heal readily to most wounds
to which they are applied. In contrast full thickness skin
grafts are more "particular" about the wound bed
to which they are applied. The process of a skin graft sticking
to the wound bed to which it is applied is known as "take".
Wounds covered with split thickness skin grafts tend to
shrink as the wound heals. This often produces an irregular
appearance to the skin graft. In contrast, full thickness
skin grafts remain flat over time and there is little wound
shrinkage.
Split thickness skin grafts tend to be a poor cosmetic match
for most wounds. Following their use there is often a residual
contour deformity and permanent differences in the coloration
of the graft compared to the surrounding skin. With time
this mismatch of coloration tends to change and may darken
or lighten compared to the surrounding skin. Full thickness
skin grafts however, tend to blend well with the surrounding
skin; this is particularly good when skin from near by areas
is used to mend a particular wound.
Whilst any type of skin graft is taking the graft needs
to be carefully immobilised. Movement between the graft
and the wound bed prevents the in-growth of new blood vessels,
which are essential for graft healing.
Indications
Skin grafts are indicated to close any wound were there
has been loss of skin and sometimes fat and occasionally
muscle or other tissues. For a skin graft to take to the
wound to which it is applied it must have a good blood supply.
Skin grafts will not take on bare bone, bare cartilage or
foreign materials such as metal or joint implants. Split
thickness skin grafts are usually used when large wounds
need to be covered, due to the plentiful nature of their
donor sites in most situations. Full thickness skin grafts
are ideal for repairing small defects, particularly on the
face, where good cosmetic matching is important.
Anaesthetic
General anaesthesia or local anaesthesia may be used. General
anaesthesia is necessary when large areas of split thickness
skin graft need to be harvested but small moderate size
grafts can be harvested under local anaesthesia. In most
cases full thickness skin grafts can be harvested under
local anaesthesia.
Technique
Split thickness skin grafts are harvested with a special
instrument known as a dermatome. The dermatome may be power
driven or may be specialised hand held knife. A thin slither
of skin is shaved from the donor site using the dermatome.
The donor site is then dressed and the wound heals under
these dressings. The harvested split thickness skin is transferred
to the wound for which it is needed. The transferred split
skin graft is held in place using dressing, stitches, staples
or glue until the graft has taken. The process of skin graft
take takes about five days.
Harvested split skin is sometimes perforated using a special
machine, known as a mesher, prior to its application. A
mesher cuts hundreds of small holes in the graft so that
the graft can be expanded. A meshed skin graft looks rather
like a string vest. As the graft settles the spaces between
the "string" heal over.
Full thickness skin grafts are cut from their donor site
using a standard surgical scalpel. After the graft has been
cut the donor site is stitched up using simple stitches
to leave a straight-line scar. The harvested full thickness
skin is then stitched into the wound where it is needed.
Dressings are applied and again these are left in place
for approximately five days whilst the skin graft heals.
Length of Operation
This is extremely variable and is mainly dependant upon
the wound that needs to grafted rather than the skin graft
itself.
Time in Hospital
Again this is variable, many grafts are applied as local
anaesthetic outpatient procedures but some grafts are used
in very major surgery lasting many hours requiring several
days stay in hospital.
Post Operative Discomfort/Limitations
Some pain following the harvesting of split thickness skin
grafts are typical. Patients commonly say that the donor
site from where the graft has been taken is more uncomfortable
than the wound to which it was applied. These donor sites
are like bad grazes and the burning sensation typical of
a graze is often associated with these donor sites. This
pain is controlled with the use of local anaesthetics at
the time of surgery and postoperative pain relieving medication
as needed. The dressing is left in place on split thickness
skin graft donor sites for between ten and fourteen days.
At this stage the dressing is removed and the donor site
should have healed. The donor site of a split thickness
skin graft is typically very red or purple when the dressing
is first removed. This redness takes several months to fade
but in the majority of cases this fades to a barely noticeable
mark.
The donor sites created when full thickness skin grafts
are harvested and the wounds to which these grafts are applied
are not particularly painful. Local anaesthetic is injected
at the time of surgery and this helps minimise postoperative
pain. Should pain relief be needed then this can be taken
as required. Full thickness skin graft donor sites are usually
stitched.
Following skin graft procedures neither the wounds grafted
nor the donor sites ever return completely to normal. Grafted
wounds commonly have some colour mismatch with the surrounding
skin and there may also be a contour deformity. The degree
of contour deformity mainly depends upon the amount of tissue
that the skin graft is replacing and the type of skin graft
used. Skin grafts typically feel numb and this is usually
a permanent feature. Permanent scars are left whenever skin
grafts are used. These scars usually settle to a flat patch,
but when split thickness skin grafts are used these scars
may remain unsatisfactory.
Time Off Work
This is typically more related to the reason for the skin
graft rather than the skin graft itself.
Risks And Complications
Donor site - for both types of skin grafts the donor sites
may fail to heal and may require a skin graft procedure
themselves to allow the donor wounds to heal up. Occasionally
skin grafts fail to take. This is usually delayed wound
healing rather than complete failure of wound healing. Some
bleeding from split thickness skin graft donor sites is
typical but this controls itself. Bleeding, bruising, swelling
and infection may complicate any donor site.
Unsatisfactory scaring - Skin graft donor sites typically
heal well (see above). Split thickness skin grafts may occasionally
lose the normal skin pigmentation and occasionally become
darker than the surrounding skin. This is more common in
individuals with dark skin.
