Keywords
Skin surgery - Skin - Photomicrography - Cadaver - Histology
INTRODUCTION
Split-skin grafts can be harvested from any part of the body using a hand-held or
power-driven dermatome. A split-skin graft provides a simple method of wound closure
when primary closure is not possible or healing by secondary intention is undesired
or prolonged. Common donor sites include the lumbar region, buttock, thigh, and arm.
The ideal donor site characteristics are highlighted in [Table 1]. In clinical practice, when the defect size is small to moderate, the thigh is frequently
chosen as the donor site of choice because: 1) it has the largest surface area of
any limb, 2) its location provides easy access and setup for graft harvesting when
the patient is in a supine position, 3) its firm underlying structures provide a stable
platform for the dermatome, and 4) the resultant scar is usually minimal and can be
easily hidden under clothing.
Table 1.
Characteristics of the ideal donor site for split-thickness skin grafts
|
Characteristics
|
|
Ease of access during surgery
|
|
Ease of preparation
|
|
Ease of harvesting
|
|
Minimal bleeding
|
|
Minimal pain
|
|
Uncomplicated postoperative care
|
|
Low risk of infection
|
|
Rapid healing
|
|
Minimal scarring or pigmentation changes
|
|
Minimal disturbance with rehabilitation
|
However, delayed donor site healing is a frequently encountered complication. Cosmetically
unacceptable hypertrophic scarring and pigmentation changes have also been described
[1]
[2]. Consequently, numerous studies have attempted to determine which dressing is optimal
to expedite donor site healing. Although some studies have recommended specific dressings
[3]
[4], others have reported no difference in healing times [5]
[6]. Interestingly, Giele et al. [7] observed no difference between the commonly used calcium alginate dressings and
adhesive retention dressings [8]. Grafting the donor site to accelerate healing has been recommended [9], while some advocate the scalp as the donor site of choice [10]
[11]. The scalp has been shown to heal more quickly than other areas but the head must
be shaved [10]. However, complications such as folliculitis, alopecia, and blood loss can occur
on the scalp [10]
[12]. Nevertheless, it has been suggested that the rich blood supply and thick dermis
of the scalp lead to rapid healing, independent of the type of dressings used.
The dermis does not regenerate once it is harvested. The epidermal layer, however,
reepithelizes through the migration of epidermal cells originating from hair follicles
and adnexal structures within the dermis [13]. Hence, donor site healing is primarily influenced by the depth of the graft harvest,
which consequently determines the thickness of the residual dermis available for reepithelization.
For this reason, it would be intuitive to opt for a donor site with the thickest dermis
whenever possible to prevent visible scarring and preserve as much of the remaining
dermal layer as possible.
Since the thigh is routinely used as the preferred donor site, we aimed to establish
the optimal region of the thigh for harvesting split-thickness skin grafts. Anecdotal
evidence suggests that the anterolateral aspect of the thigh has thicker skin than
that in the anteromedial aspect. To our knowledge, no published literature has confirmed
this assumption. We hypothesized that the anterolateral thigh region is the optimal
donor site based on thickness measurements. Therefore, we aimed to assess variations
in skin thickness from the anteromedial, anterior, and anterolateral regions of the
thigh and their corresponding epidermal thickness in a cadaveric study. To measure
true skin thickness, we designed a novel precision equipment for sectioning skin specimens
and applied an unbiased stereological method to determine skin thickness.
METHODS
Full thickness skin specimens were sampled from the anteromedial, anterior, and anterolateral
regions of the thigh of formaldehyde-fixed human cadavers (n=6) from the Department
of Anatomy. Unsystematically sectioning the skin specimens introduces inaccuracy in
the measured thickness of the specimen. However, slicing the skin specimens accurately
at right angles avoids overestimating the thickness during sampling ([Fig. 1]). To ensure that the true epidermal and dermal thicknesses were sampled, a custom-made
precision apparatus was designed and used in this study.
Fig. 1
Micrograph of stained skin specimensMicrograph demonstrating that unsystematically
sectioning the skin specimens at various angles (yellow arrows) introduces inaccuracy
into the thickness measurement. Slicing the skin specimens accurately at right angles
(red arrows) avoids overestimating the thickness during sampling.
This apparatus consists of a plastic base component and a metal top component that
can be secured together ([Fig. 2A]). The skin specimen is placed between the two components and securely locked. The
metal component is designed to incorporate parallel slits where scalpel blades can
pass at right angles to section the specimen ([Fig. 2B]). These slits were set at widths of 1 mm, 2 mm, or 3 mm.
Fig. 2
Custom made skin-sectioning apparatus(A) A skin specimen is placed between the plastic
base component and the metal top component of a custom-made precision instrument that
has predetermined slit thicknesses to allow skin sectioning at a right angle with
a scalpel. (B) A 1-mm thick piece of cadaveric skin sectioned at a right angle was
obtained.
The combined epidermal and dermal thicknesses were measured using a standard digital
calliper. Sectioned skin samples were stained with a dilute solution of haematoxylin
and toluidine blue ([Fig. 3A]). Microscopic images were captured with a digital camera at 10× magnification (Leica
Camera AG, Wetzlar, Germany) ([Fig. 3B]). Subsequently, the epidermal thickness was determined by employing a stereological
method as described by Jensen et al. [14] to overcome observer and measurement bias.
Fig. 3
Sections stained with haematoxylin and toluidine blue(A) Images of stained skin sections
were captured using a microscope mounted with a digital camera at 10× magnification.
(B) Note the variable position of the basement membrane, which results in a variable
epidermal thickness.
Briefly, a standard grid of 21×11 points was transposed onto each digital image of
the skin section ([Fig. 4A]) using image analysis software (ImageJ version 1.43, National Institutes of Health,
Bethesda, MD, USA). All points where the grid points coincided with the basement membrane
on the image were noted. Since the epidermal thickness is variable across the section
of skin, the grid provided random points on the image where epidermal thickness can
be measured. The epidermal thickness was measured perpendicular to the surface of
the epidermis at these pre-determined random points ([Fig. 4B]). At least six images were taken from each skin section and at least five sections
were obtained from each region of each cadaver.
Fig. 4
Stereology method to overcome observer bias(A) A uniform grid was transposed on the
image (red crosses) and any points that coincided with the basement membrane (highlighted
with white crosses) were noted for measurements. (B) The epidermal thicknesses were
measured perpendicular to the surface of the epidermis using image analysis software
(highlighted with white arrows).
The measurements were entered into a Microsoft Excel spread sheet (Microsoft Co.,
Redmond, WA, USA) and statistical analyses were performed using GraphPad InStat version
3 for Macintosh (GraphPad Software Inc., San Diego, CA, USA). We utilized one-way
analysis of variance to test the differences in thickness measurements among the regions
and subjects. Statistical significance was set at P<0.05.
RESULTS
Epidermal thickness
We found a statistically significant difference in epidermal thickness measurements
between subjects (P<0.05). Epidermal thickness represented 2.5% to 9.9% of the overall
skin thickness.
In addition, when different regions of the thigh were compared, there was a significant
difference in epidermal thickness between regions (P<0.05). The anterolateral thigh
region had the highest mean epidermal thickness and the most consistent epidermal
thickness (60±3.2 µm) between subjects ([Table 2]).
Table 2.
Comparison of skin thicknesses for each region
|
Characteristic
|
Overall skin thickness (epidermal and dermal)
|
Epidermal thickness
|
Comparison of epidermal thickness
|
|
Values are presented as mean (μm)±standard deviation.
|
|
Anteromedial
|
1,032 ± 435
|
55 ± 12.5
|
P < 0.05
|
|
Anterior
|
1,063 ± 301
|
57 ± 9.4
|
P < 0.05
|
|
Anterolateral
|
1,220 ± 257
|
60 ± 3.2
|
Not significant
|
Overall skin thickness
Similarly, there was a statistically significant difference in overall skin thickness
between subjects (P<0.05). The overall skin thickness was measured as 1,032±435 µm
in the anteromedial region compared to 1,220±257 µm in the anterolateral region ([Table 2]).
In five of the six subjects, there were statistically significant differences in skin
thickness measurements (P<0.05) when different regions of the thigh were compared.
Overall skin thickness increased as we moved laterally from the anteromedial region
of the thigh to the anterior and anterolateral regions ([Fig. 5]).
Fig. 5
Overall skin thickness (combined epidermal and dermal)In the majority of cases (except
C6), there were statistically significant
differences in skin thickness measurements (mean±standard deviation) when different
regions of the thigh (anteromedial [AM], anterior [ANT] and anterolateral [AL]) were
compared (P<0.05).
DISCUSSION
The choice of a split-thickness skin graft donor site can be influenced by the surgeon's
preference or the patient's choice ([Table 1]). In addition, the defect size, technical limitations, potential morbidity, patient
position, and ease of access to the donor site can also be relevant. While these considerations
may be less important when resurfacing large surface areas, small- to moderate-sized
wounds deserve a balanced debate about which donor site will optimize healing.
In this study, we compared the skin thickness in the anteromedial, anterior, and anterolateral
aspects of the thigh, as they are the most common donor sites in clinical practice.
The skin of the ventral, outer, and dorsal aspects of the thigh has been described
as of intermediate thickness for the purposes of skin grafting [15]. The anterior and anterolateral aspects of the thigh are usually favoured because
of their flat surfaces, while the anteromedial aspect may be preferred because of
its relatively concealed location.
To optimize measurement accuracy, we developed a method to prepare skin sections using
a custom-made apparatus. Random point selection using a grid was employed to eliminate
observer bias when measuring epidermal thickness. Following these protocols to overcome
potential sampling inaccuracy and observer bias, we found that the anterolateral thigh
region was the optimal donor site. Despite subject-to-subject variation, the anterolateral
thigh exhibited highest epidermal and overall skin thickness; moreover, the epidermal
thickness measurements were relatively consistent across subjects.
We recognize that the number of cadavers used in this study was small and the use
of fixed cadaveric skin specimens has the theoretical drawback of being susceptible
to potential shrinkage. Although some controversy exists regarding the extent of shrinkage,
previous published work dealing with tissue fixation can give an indication of the
expected degree of tissue shrinkage. Using liver tissue, Fox et al. showed that a
mere 3% of shrinkage occurred when tissue samples were fixed at room temperature,
but that shrinkage was negligible when fixed at 37℃ [16]. Cutts [17] reported no significant loss in muscle length when muscle tissues were fixed in
situ on the skeleton, compared with a small loss (2%) in length when fixed in isolation.
Data on the shrinkage of cutaneous tissue following tissue fixation are less conclusive.
Hudson-Peacock et al. [18] demonstrated that skin specimens shrank by 31% after fixation, with most of the
shrinkage (22%) occurring during the post-excision/pre-fixation phase. However, Golomb
et al. [19] showed that 94% of shrinkage occurred after excision and before formalin fixation.
Contrastingly, Gregory et al. [20] reported a 22% shrinkage of skin specimens with equal contributions from both post-excisional/pre-fixation
shrinkage and post-fixation shrinkage, but their study size was small. Interestingly,
Kerns et al. [21] reported that skin excision specimens shrunk immediately after excision due to their
intrinsic contractile properties but re-expanded slightly when immersed in formalin.
Another recent report by Dauendorffer et al. [22] similarly showed that shrinkage of skin specimens occurred immediately after excision
but the specimens did not show significant changes following fixation. Thus, extrapolating
from these reports, we could infer that the fixation-related shrinkage of skin specimens
varies between 0% to a maximum of 10%. We believe that if this study were to be repeated
in a clinical setting, the majority of shrinkage would occur immediately following
excision, due to primary skin contraction, and before specimen preparation. Therefore,
we believe that our present findings would not be markedly different from that of
a study using fresh tissue.
Interestingly, a recent survey of the general female population showed a preference
for posterior donor sites in the buttock, lower back, and thigh [23]. A previous study also found that the buttock was the donor site of choice amongst
surgeons if they were to undergo skin grafting themselves [24]. In paediatric patients with burns, although there were no differences one year
after grafting, posterior donor sites had a better cosmetic appearance compared to
thigh donor sites at one year after grafting or earlier [25]. Future studies including the buttock, lower back, and the posterior thigh should
be carried out to evaluate skin thickness at these sites. Furthermore, measurements
of freshly frozen cadaveric tissues or clinical specimens could be performed to confirm
our observations.
Our cadaveric study confirms that the anterolateral thigh is the optimal site for
harvesting split-thickness skin grafts. Based on skin thickness measurements, the
anterolateral thigh has the thickest epidermal and dermal layers. We suggest that
the anterolateral thigh region should be the donor site of choice for split-skin graft
harvests from the thigh.
