Variation of skin thickness over the equine body and the correlation
between skin fold measurement and actual skin thickness
Drs M.E. Volkering
Student number: 0353051
December 2009
Project tutors:
J.M. Wilmink (Woumarec, Wageningen)
M. Moleman (Faculty of veterinary medicine, University Utrecht)
1. Contents
Contents
2
Samenvatting
3
Abstract
4
Introduction
5
Materials and Methods
6
Results
8
Discussion
11
Materials used
13
References
14
Dankwoord
15
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1. Samenvatting
Dat de huiddikte bij paarden over het lichaam varieert is bekend, maar de mate van variatie
is niet exact bekend. Tijdens dit onderzoek zijn er bij 9 verschillende warmbloedpaarden, op
28 verschillende plaatsen in het totaal 490 biopten genomen. Van deze biopten is vervolgens
met behulp van een digitale schuifmaat onder een vergrootglas de dikte bepaald. Ook is er
wanneer dit mogelijk was voorafgaand aan de bioptie de dikte van de huidplooi bepaald met
behulp van een micrometer. Er kon geen significante correlatie worden aangetoond tussen de
dikte van de plooi en de dikte van het biopt.
De huiddikte varieerde van 1.47mm ter hoogte van het lieskanaal, tot 4.57 mm aan de
dorsale zijde van het achterbeen 1.5cm boven de hoef. Verder is de huid op de rug het dikst en
de huid op het hoofd, nek en het ventrale abdomen het dunst. De huid op de benen is met
2.86mm niet erg dun, terwijl er soms wel gedacht wordt dat de huid op de benen dun is. Naar
distaal wordt de huid op de benen dikker, verder is er geen significant verschil in de huiddikte
van de voor- en achterbenen.
De informatie over de huiddikte is van belang bij het uitvoeren van huidtransplantaties
kan daardoor bijdragen aan een optimaal wondmanagment.
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2. Abstract
It is known that there is variation in the thickness of the skin between between the different
bodyparts, but the exact variation is not known. During this study we performed 490 biopsies,
on nine horses and 28 different places on the equine body. Of these biopsies the thickness is
measured with a digital sliding under a magnifying glass. If there was a possibility we first
measured the thickness of a skinfold with a micrometer. There was no significant correlation
between the thickness of the fold and the biopsy.
The tickness of the skin varies from 1.47mm on the external inguinal canal to 4.57 on
the dorsal side of the hindlimbs 1.5cm above the hoof. The skin on the back is the tickest and
the skin on the head, neck and ventral abdomen is the thinnest. The skin on the legs is 2.86mm
and it is not thin, in contrast which is thought in many cases. The skin of the limbs becomes
thinner the more distal on the legs. There is no significant difference in the thickness of the
skin of the front- and hindlimbs.
Knowledge about the skin thickness is important in harvesting skingrafts and can
contribute to an optimal woundmanagment.
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3. Introduction
The thickness of horse skin varies1, as many equine veterinarians already experience in
practice during surgery. It varies not only between horses, but also between different parts of
the body of the individual horse. Knowledge about the thickness of skin is important during
skin grafting.
Skin grafting in horses plays an important role during the management of large fullthickness limb wounds, and aims for faster healing and better functional and cosmetic results4.
However, the results of skin grafting depend on the technique used and the recipient site. The
results are additionally influenced by the thickness of the grafts. Thin partial thickness grafts
are more readily accepted but more vulnerable and less cosmetic. Thick partial thickness
grafts or full thickness grafts are less readily accepted but when accepted they are more
durable and provide a better cosmetic result. The most successful technique used for skin
grafting in horses is the Meek micrograft technique2, during which partial thickness
micrografts are used that are easily accepted even when thick partial thickness grafts are used.
Therefore it is aimed for harvesting the donor skin as thick as possible because this results in a
stronger and a cosmetic nicer scar with more adnexa.
The thickness of the donor skin is difficult to be estimated because of the variation between
individual horses and thus the dermatome appears not always to be adjusted for optimal
cutting depth. When it is set too thin, the graft is thinner which means that the graft will be
more vulnerable and contains less or no hair follicles. When it is set too thick, the dermatome
will cut through the subcutaneous tissue instead of the dermis and create a full thickness graft
which is not desirable for the Meek micrograft technique. If a correlation would exist
between skin thickness and the thickness of a skin fold measurement at the same location, this
may provide an easy method to acquire information about skin thickness and successively the
adjustment of the dermatome for an individual patient.
There is no scientific information about skin thickness in horses nor about practical methods
to estimate this thickness for grafting procedures. Therefore the aim of this study is to map
skin thickness over the body of 9 Warmblood horses and to determine the correlation between
skin fold and skin thickness. There is scientific information about the skin thickness in
humans, it is known that knowledge about the skin thickness may be useful by harvesting fullor split-thickness skin grafts3.
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4. Material & Methods
Horses
For this study, nine Dutch Warmblood horses, that were humanely euthanized for reasons
unrelated to the skin, were used. The mean age of the horses was 8,06 (±5,15) years and the
mean weight was 567(± 61) kg.
Sampling and measuring techniques
Sample taking took place within 4,5 (±3.2) hours after euthanasia.
Anatomical sampling sites were standardised and symmetrical on left and right side of the
body (Figure 1). The sampling sites were shaved1 before measurement. The skin was lifted at
the sampling site with rat-toothed forceps and the thickness of this fold was measured with a
micrometer2. After this measurement a punch biopsy3 of ø 8 mm was taken 5 mm next to the
place were the thickness of the fold was measured, since fold measurement caused a slight
compression of the tissue. After taking the biopsy, the thickness of the biopsy was defined
under a magnifying glass with a digital caliper4, the total thickness of epidermis and dermis
was measured.
Statistics
The results of this survey were analysed in SPSS. We used a mixed model to prove if there
are significant differences between the skin thickness over the body, and if there is a
relationship between the thickness of the fold and the thickness of the skin. Significance was
set at 0.05.
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Figure 1. The places where the thickness is measured.
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5. Results
Skin thickness varied from 1.47 to 4.57 mm. (Table 1 and Fig 2**met kleurtjes) depending on
anatomical location. The location with the thinnest skin is the external inguinal canal (1.47 ±
0.29 mm) whereas the thickest skin is the dorsal side of the coffin joints of both front- and
hind limb (4.54 ± 0.38 mm) being 3 times thicker. The skin thickness tapers off from the back
to side to the ventral abdomen (Table 1, Fig 2). The skin on the limbs increase in thickness
more distally on the limbs. Additionally, the skin on the lateral side of the limb is thicker than
the skin on the medial side (Table 1, Fig 2).
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1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Head
Between medial corner of the eye and
median, 3 cm out median
Centre of the masseter muscle
Neck
Lateral to 2nd cervical vertebra
Lateral to 5nd cervical vertebra
Back
Lateral to the withers, dorsal of the
scapular cartilage
Lateral to L6 5 cm out of the median
Halfway between wings of the ileum-and
the base of the tail
Halfway between tuber coxae and tuber
ischiadicum
Side
Midway the caudal margin of the scapula
Midway the 15th rib
10 cm behind the costal arch
Ventral abdomen
In the centre of the pectoral muscle
Between the frontlimbs 5cm out of the
median
On the costal arch 15 cm out of the
median
15 cm cranial to umbilicus, 5cm out of the
median
At the umbilical scar, 5 cm out of the
median
Over external inguinal canal
Frontlimbs
Lateral midway radius
Medial midway radius
Dorsal side of the carpus
Midway dorsal metacarpus
Dorsal coffin joint, ? cm proximal to
coronary band.
Hindlimbs
Between the semimembranosus and
semitendinosus muscle
Lateral midway tibia
Medial midway tibia
Dorsal side tarsus
Midway dorsal metatarsus
Dorsal coffin joint, ? cm proximal to
coronary band.
Table 1: Skin thickness per anatomic sampling site
Thickness of the biopsy SD (+/-)
in mm (+/- SD)
1.73
0.16
1.77
0.21
1.69
2.03
2.02
2.05
3.32
3.02
0.18
0.20
0.21
0.23
0.54
0.58
4.36
3.34
1.08
0.62
2.55
0.33
2.74
2.15
3.06
3.06
1.94
1.86
2.04
0.55
0.27
0.74
0.75
0.18
0.20
0.23
2.27
0.33
2.02
0.23
1.94
0.31
1.47
2.83
2.00
1.96
3.03
2.75
4.51
0.29
0.27
0.28
0.32
0.46
0.37
0.38
2.89
2.33
0.24
0.30
2.47
2.18
2.55
3.27
4.57
0.37
0.30
0.51
0.38
0.40
Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
Figure 2: Skin thickness over the body
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Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
There was no significant difference between the left and right side of the body, and no
significant difference in the thickness of the skin on the front and hind limbs in the same
anatomical location. On the back, the mean skin is the thickest 3.32 mm ± 0.54 and
significantly different from, the skin on the head, neck and abdomen (resp 1.73, 2.03,
1.94)(Fig 2, Table 1,2).
Head
Neck
Back
Side
Head
Neck
Back
Side
Abdomen Frontlimbs Hindlimbs
-
0.075
0*
0*
0.132
0*
0*
-
0*
0*
0.494
0*
0*
-
0*
0*
0*
0*
-
0*
0.519
0.268
-
0*
0*
-
0.61
Abdomen
Frontlimbs
Table 2. The P-values between the anatomical locations after testing in a mixed model test (SPSS),
* = The difference between those locations is significant.
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Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
In figure 3 it is seen that it looks like there is a relation between the tickness of the skin and
the skin fold. The correlation coefficient between the thickness of the skin fold and the
measured skin thickness in the biopsies is 0.385.The P-value of the correlation 0.012 which is
not significant (Fig 2). There was 174 times of the 490 (35,5%) times we took a biopsy, the
possibility to measure the fold.
Thickness biopsy
Correlation thickness skinfold- biopsy
4,5
4
3,5
3
2,5
2
1,5
1
0,5
0
0
1
2
3
4
5
Thickness skinfold
Figure 3: Correlation between thickness of skinfold and biopsy thickness.
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6
Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
6. Discussion
The most of the results where as we expected, the skin on the back is thick, on the head and
the ventral abdomen thin. It was unexpected that the skin on the limbs was that thick, the skin
dorsal on the coffin joint (1.5 cm above the coronary band) is the thickest skin found. A
possible explanation might be that the skin has to protect the legs. Underneath the skin on the
legs there is little soft tissue so the skin needs to be strong and give resistance to daily stress.
Another remarkable point during this research is that there was much difference in the
thickness of the skin lateral to the withers (SD ± 0.58) between the horses. This could be due
to the fit and use of a saddle, as one horse with an old saddle sore (marked by white hairs
lateral on the withers) had thick skin lateral on the withers, 3.86 mm, 0.84 mm over the
average.
The skin in the lumbal region is the thickest skin on the back and has a large standard
deviation as well (4.36 mm ± 1.08) .The reason for this and other individual variation between
the horses is unknown, but the body condition and gender of the horse and it’s genetical
background might be of influence. In humans it is known that there is a difference between
males and females3. Further research is needed to shed light on this matter.
There were two cases the results of one frontlimb are missing, this is because this limb was
removed of the horse for pathology. In that case only the results of the other frontlimb are
used.
During this study there were sometimes difficulties, especially with the measuring of the skin
fold. Many times it was impossible to lift the skin and make a fold. We were only 174 times
able to pull a fold wich could be measured, this is 35,5%. A reason why we could not measure
the fold was that the skin is too tight attached with the underlying tissue, specific on the back
of the horse and on the front of the head. Also the post mortem production of gas is a reason
there is much pressure on the abdominal wall, which makes it sometimes impossible to pull a
fold. Sometimes the thickness of the fold is thicker than expected. This is possibly because
there is some subcutaneous tissue involved in the fold. Because of these reasons there are a
great number of places where the thickness of the fold could not be measured, there are not
that many results and this might be one of the reasons that there could not be proved a relation
between the thickness of the skin fold and the biopsy. Measuring the thickness of the skin by
ultrasound might be a better way to get an idea of the skin thickness in a non-invasive way. In
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Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
humans a 20 Hz ultrasound is used for a reliable measurement of the skin thickness5,6.
Furthermore it would be of great value to know more about the ratio of epidermis/dermis.
The knowledge of skin thickness at the donor site is essential to achieve the optimal result in
skin grafting
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Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
7. Materials used:
1
= Gilette razor, with disposable blades
2
= Suhl, micrometer.
3
= Stiefel, punch biopsy ø 8 mm.
4
= Gedore, digital calliper No. 711 150 mm.
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Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
8. References:
1) Auer JA and Stick JA. Equine surgery, 3th edition(2006), Page 274
2) Wilmink JM, Van Den Boom R, Van Weeren PR, et al: The modified Meek technique as a
novel method for skin grafting in horses: evaluation of acceptance, wound contraction and
closure in chronic wounds. Equine Veterinary Journal 2006;38:324
3) Lee Y, Hwang K. Skin thickness of Korean adults. Surg Radiol Anat (2002) 24: 183-189
4) Stashak TH, et al: Equine wound management, 2nd edition (2009), Chapter 11
5) Kong L, Caspal J, Duckworth M, Sprigle S. Assessment of an ultrasonic dermal scanner
for skin thickness measurements. Medical Engineering & Physics 30 (2008) 804-807
6) Moore TL, Lunt M, McManus B, Anderson ME, Herrick AL. Seventeen-point dermal
ultrasound scoring system- a reliable measure of skin thickness in patients with systemic
sclerosis. Rheumatology 2003;42:1559-1563
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Variation of skin thickness over the equine body and the correlation between skin fold
measurement and actual skin thickness
9. Dankwoord
Allereerst wil ik Jacintha bedanken, zij is de initiatiefneemster van deze onderzoeksstage. Ik
heb veel van haar geleerd, van haar positieve instelling en al haar kennis op het gebied van
huid, wondgenezing en alles wat hier mee te maken heeft. Dan de begeleider vanuit de UU
Maarten, ook jij stond altijd voor mij klaar met allerlei praktische tips en bemoedigende
woorden (zoals de wetmatigheid dat je al je gegevens vanuit excel altijd weer moet
veranderen voordat ze in SPSS geanalyseerd kunnen worden). Verder heb jij geregeld dat ik
bij de Lingehoeve terecht kon voor de monstername. Daar werd ik altijd gastvrij ontvangen en
aan de koffietafel was het erg gezellig, dus ook de Lingehoeve en dan Peter Wiemer in het
bijzonder bedankt! Verder heb ik statistiek gedaan, dit was nooit gelukt zonder de hulp van
Jan van de Broek.
Tijdens dit onderzoek heb ik de gelegenheid gehad om het gehele traject van
onderzoeksvoorstel tot het schrijven van het verslag, wat als basis van een artikel dient, te
doen. Dit was ontzettend leerzaam en niet altijd even makkelijk (in de kou en het donker op
de kadaverplaats). Maarten en Jacintha ontzettend bedankt, ik vond de samenwerking heel erg
plezierig!!
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