MR3127
BSc (Hons) Dissertation Farriery Science
A pilot study into specific metacarpal measurement
variants causing asymmetry and there relationship to
coronary band width between right and left equine fore
limbs in fifteen matched pairs of morbid specimens.
David A Hall Dip WCF (Hons) FdSc
Student number: 20118021458571
Word Count: 10,034
David Hall FdSc Dip,WCF Hons April 2013 1
Acknowledgements
I would like to thank the staff at Myerscough College for their tuition through out
the five years of this course. I would like to take this opportunity to also thank
Mark Caldwell for his friendship and guidance, and Loraine Allan for stepping in at
the last minute with her excellent style of teaching. I would like to acknowledge
my fellow students on this course for all pulling together and helping each other
when it got to hard, without the camaraderie it would not have been possible to
complete the course. For those that helped with computer skills and literacy along
the way and my family for there help and patience.
David Hall FdSc Dip,WCF Hons April 2013 2
Abstract
Introduction
There is a lot of anecdotal evidence that links asymmetric limb length and miss
matched feet with performance and future pathology, little is known about the
individual elements that go to make up the asymmetry in the fore limb.
Study design
A quantitative experimental pilot study.
Hypothesis
Is there asymmetry in bone measurements taken from the third metacarpal between
right and left fore limbs of the same horse and is there a relationship with miss
matched feet.
Aim
Too test the hypothesis that there is a relationship between metacarpal length, width
and circumference with coronary band width.
Objective
To test the length and other measurements of the third metacarpal to see if there is
asymmetry in the bone, to measure coronary band width and see if there is a
relationship.
Materials and Method
In a pilot study of 15 matched pairs of fore limbs freshly amputated below the carpus
3 measurements of the third metacarpal were taken, the overall length of the bone,
the width of the bone at mid shaft and the circumference of the bone at mid shaft, to
determine if asymmetry existed in theses measurements. The coronary band width
was also measured to determine if the feet were mismatched. The bone
David Hall FdSc Dip,WCF Hons April 2013 3
measurements were then compared to the coronary band width using computer
software (Microsoft Excel ® and Minitab 16®) to see if there was a correlation
between the two measurements.
Results
Asymmetry was found in the Mid shaft circumference of the third metacarpal in 14
out of 15 of the matched pairs of bones, 13 of the circumferences measured were
larger in the left limb than the right limb, and one pair was larger in the right limb than
the left limb. There was a strong correlation between coronary band width
differences in the miss matched feet and the circumference differences in the third
metacarpal. No significant difference was found in metacarpal length.
Conclusion
Horses with a wider coronary band will have an increase in circumference in the mid
shaft of the third metacarpal.
Significance
The study gives further weight to the theory that miss matched feet are linked to bio
mechanical function and in some cases handedness and any alteration of this
condition should take the horse as a whole into consideration.
David Hall FdSc Dip,WCF Hons April 2013 4
Contents Page
Title page
Page 1
Acknowledgements
Page 2
Abstract
Page 3
Table of contents
Page 5
Chapter 1 – Rationale and introduction
Page 8
1.1 Rationale
Page 8
1.2 Introduction
Page 8
1.3 Anatomy of the lower limb
Page 10
Chapter 2 – Literature review
Page 13
2.1 Introduction
Page 13
2.2 Review
Page 13
2.3 Asymmetry in the long bones
Page 13
2.4 Asymmetry in the equine third metacarpal
Page 14
2.5 The hoof capsule
Page 16
2.6 Bio mechanics
Page 18
2.7 Handedness
Page 19
David Hall FdSc Dip,WCF Hons April 2013 5
Chapter 3 – Methodology
Page 21
3.1 Introduction to methodology
Page 21
3.2 Aims of the study
Page 21
3.3 Hypothesis
Page 21
3.4 Experimental design
Page 22
3.5 Ethical consent
Page 22
3.6 Objectives of the research
Page 22
3.7 Experimental procedure
Page 25
3.8 Data collection
Page 26
3.9 Data analysis
Page 27
3.10 Procedural check list
Page 27
Chapter 4 – Results
Page 29
4.1 Group demography
Page 29
4.2 Environmental standardisation
Page 29
4.3 Discussion of results on raw data
Page 30
4.4 Statistical analysis
Page 31
4.5 Metacarpal Length
Page 31
Chapter 5 – Discussion
5.1 Metacarpal Asymmetry
Page 36
Page 36
David Hall FdSc Dip,WCF Hons April 2013 6
5.2 Coronary Band Width
Page 36
5.3 Relationship between coronary band width and third metacarpal length Page 36
5.4 Limitation of Study
Page 38
Chapter 6 – Conclusion and recommendations
Page 38
Chapter 7 – Clinical relevance
Page 39
7.1 Clinical relevance of the asymmetry
Page 39
7.2 Asymmetry in the hoof shape
Page 39
Reference List
Page 40
Bibliography
Page 43
Appendices
Page 44
David Hall FdSc Dip,WCF Hons April 2013 7
Chapter 1
Introduction and rationale
Rationale
A study by Watson (2003), the third metacarpal was measured by x-ray in the right
and left fore limb in thoroughbred race horses. The study showed differences in left
and right metacarpal length of between 5-9 mm in 50% of the horses measured.
Studies have indicated that a high frequency of asymmetry occurs in a random
population of horses, most notably in the height of the shoulder on the right limb
Wilson et al (2009), whilst Dollar (1898) has previously stated that the conformation
of the limbs depends on the varying lengths of the individual bones and upon the
angles they make with each other. This led the researcher to conduct this study into
bone asymmetry in morbid specimens. A proper understanding of asymmetry and its
causes will help clinicians develop a rational for treatment and an increase in the well
being of the horse.
Introduction 1.1
Much work has been done identifying the existence of asymmetry in equine front
limbs and feet. Studies have indicated that a high frequency of asymmetry occurs in
a random population of horses, most notably in the height of the shoulder on the
right limb (Wilson et al 2009), whilst Dollar (1898) has previously stated that the
conformation of the limbs depends on the varying lengths of the individual bones and
upon the angles they make with each other. In a study in Australia by Watson (2003)
the third metacarpal was measured by x-ray in the right and left fore limb in
David Hall FdSc Dip,WCF Hons April 2013 8
thoroughbred race horses. The study showed differences in metacarpal length of
between 5-9 mm in 50% of the horses measured, with 80 % of the horses exhibiting
a greater or lesser difference than this. 20% of the horses had an equal length in the
metacarpals. 76% of the horses had a longer right metacarpal. In a study on race
horses in Australia by Decurnex (2009) the proximal hoof circumference was
measured on horses during training and rest periods. A decrease in circumference
was recorded during training and the circumference of the proximal border increased
whilst the horses were out of work and in the paddock, the largest increase being in
the right fore.
Asymmetry in the hoof capsule is easily observable but difficult to quantify although
work has been done using external reference points Duckett (1990). Hoof capsule
shape and size where left differs from right constitutes asymmetry. Redden (2003)
studied asymmetry in miss matched feet, the study graded hoof angles between 1-4,
where 1 is where the hoof angle is between 3°-5° greater than the opposing foot
which would be clearly observable as an asymmetry and grade 4 being the coronary
band being further forward of the bearing border at the toe. In a recent paper on hoof
volume by Caldwell et al (2012) it was established that in a displacement test
between right and left amputated morbid hoof capsules that the hoof with the lowest
volume had the narrowest coronary band width.
Gray (2007) reported handedness in horses could contribute to limb asymmetry, this
would be difficult to prove but it is possible to cross reference other aspects of
handedness reported in humans with the observable conditions in the equine, such
as hoof capsule such size and shape differences and limb length differences. In Cuk
(2001) a paper on long bone asymmetry it stated that humerus length is reflected in
handedness in humans. If there is any form of handedness in the equine then it
should be reflected in the third metacarpal.
In a recent pilot study Caldwell et al (2012), the existence of limb length disparity
was identified using external markers on given reference points of the horse. The
study showed that in this small study that 75% of the horses demonstrated fore limb
asymmetry.
David Hall FdSc Dip,WCF Hons April 2013 9
1.2 Anatomy of the distal limb and the foot
The Third Metacarpal Bone
The third metacarpal bone is a typical long bone and is vertically orientated between
the carpus and the proximal phalanx, and is one of the strongest bones in the
skeleton. The dorsal surface is smooth, rounded from side to side and nearly straight
in length.
The palmer surface is flat from side to side. On either side is a roughened area for
the attachment of the second and fourth metacarpal bones. With the second and
fourth metacarpal bones the palmer surface of the third metacarpal forms a channel
for the passage of the suspensory ligament. The proximal extremity has an articular
surface for the distal row of carpal bones. On the dorso medial aspect is a
roughened projection, the metacarpal tuberosity, for the insertion of the tendon of the
extensor carpi radialis muscle. The distal extremity articulates with the proximal
phalanx and the proximal sesamoid bones. A sagittal ridge divides it into two
condyles, the medial being slightly larger. On either side there is a small depression
for the attachment of the collateral ligaments. . Hickman (1988)
During development of the bone in the embryo the bones are composed of Hyerline
cartilage, but by birth most of the cartilage forming the shaft of these bones has
ossified. After birth the extremities rapidly ossify to form the bony epiphyses. The
bony epiphyses are separated from the shaft by a layer of cartilage called epiphyseal
cartilage or growth plate. The bone grows in length by the proliferation of the
cartilage cells forming the growth plate and their replacement by bone. Uneven
growth of the growth plates results in angular limb deformity of the leg. . Hickman
(1988)
When bone reaches its maximum length proliferation of the cartilage cells stops and
the growth plates become completely ossified. The shaft of the bone and the
epiphyses are fused and the bone ceases to grow in length. The conformation of the
horse is established and cannot be altered. A long bone grows in overall thickness
by the deposition of the bone on the surface from the inner cellular layer of the
periosteum. At the same time the marrow cavity is enlarged by the reabsorption of
David Hall FdSc Dip,WCF Hons April 2013 10
bone. Closure of the growth plates of the third metacarpal occur at one year with the
rapid growth of the bone occurring at 0-3 months. Hickman (1988)
Coronary Band Width
The coronary band is the area at the proximal aspect of the hoof capsule and
combines the production of the hoof wall from the coronary corium with a flexible
union between the dermis or horse’s skin and the hoof wall Stashak (1996). The
width of the coronary band will be affected by the distal phalanx and the attached
lateral cartilages and the angle they occupy within the hoof capsule. This will also be
affected by the structures above the capsule composed of bones, ligaments, tendons
and muscles. The flexible lateral cartilages are attached to the distal phalanx
medially and laterally extending palmarly past the last point of the wing of the distal
phalanx they give shape and form to the posterior of the capsule. They extend
proximally and are situated half in the capsule and half out. They can be palpated
just above the coronary band and situated between them between them is the digital
cushion which gives shape to the bulbs of the heels.
The hoof is designed to with stand the incredible static and dynamic forces to which
it is subjected. In Lungwitz (1908) he used closed electrical circuits to establish the
order of the capsule deformation, he established in a bare foot model that the heels
expand on ground impact as the caudal parts of the foot are loaded shown in fig 1.1.
The distal phalanx rotates caudally ventrally thus transmitting weight to the laminar
interface. The coronary band descends as the dorsal wall becomes concave and the
sole flattens. This is also reported by Roepstorff (2001).
David Hall FdSc Dip,WCF Hons April 2013 11
Fig 1.1 A diagram of the hoof function under load, according to Lungwitz (1908)
Fig 1.2 shows a transverse section through the hoof capsule at the level of the
coronary band. It illustrates the structures present in the hoof which gives it shape
and is subjected static and dynamic forces placed on it.
David Hall FdSc Dip,WCF Hons April 2013 12
Chapter 2
Literature Review
2.1 Introduction
The majority of available research into bone length asymmetry has been completed
in the human medical field necessitating the extrapolation of this into farriery and
equine context. The research methods used for this study included the internet,
veterinary publications such as Equine Vet Journal and university library. The
internet research utilised scientific paper specific search engines, science direct
Wiley on-line and Google scholar.
Key search words were limb disparity, asymmetry in equine and long bones.
Coronary band width, miss matched feet in the equine and handedness.
2.2 Literature review;
Human long bones, third metacarpals, hoof capsules, bio mechanics
handedness.
2.3 Asymmetry in human long bones
Studies of the degree of asymmetry in human long bones began on the 19th century.
The most frequently used the dimensions were total length and weight measured
both in skeletons, in living people, and in archaeological collections. Although data
was gathered in different groups of people living in different circumstances all results
agree and demonstrate that bilateral asymmetry is more marked in arm bones than
the leg bones and that on average, right arm bones are longer by 1% - 3% and
heavier by 2% - 4% than the left arm bones Steele (2000).
Cuk (2001) carried out a study of the lateral asymmetry of the human long bones
based on anthropometric data of long bones of 26 female and 16 male medieval
skeletons. The results confirm the presence of orientated asymmetry more
prominent in the arms and legs. The average lateral asymmetry in the arms was
found in the right arm, and in the legs to the left leg. By far the most asymmetric
bone though was the humorous and almost all the parameters were highly significant
but particularly the circumference of the shaft, the width and the maximum length.
David Hall FdSc Dip,WCF Hons April 2013 13
These findings reflected other studies on handedness. The dominant leg is
expressed by the stronger tibia usually on the opposite side of the dominant arm.
The stronger development of the left tibia as a supportive limb is characteristic of
both right and left handedness.
2.4 Asymmetry in equine third metacarpal.
In a short communication on third metacarpal bone length and skeletal asymmetry of
the racehorse by Watson (2003) the study set out to investigate the differing lengths
between left and right third metacarpal in the same horse. The aim of the study was
to establish whether there was a consistent difference in third metacarpal length in
two independent groups of thoroughbred racehorses. The study was done using
radiographic views lateromedial of the left third metacarpal and the mediolateral
radiographic view of the right metacarpal. The radiographs were then measured for
each horse using a plastic ruler in mm between the most distal point of the proximal
joint surface and the most proximal point of the distal condyles.
The sample size of 46 racehorses in two yards seems to be an adequate number for
the study. There was no mention of any exclusion criteria in the experiment and no
mention of ethical consent.
They were aged between 2-6 years and had raced or were in training at racing
speed at the time the radiographs were taken. The measurement process used an
interesting validation method of using the x-ray machine to compare the contralateral measurements, as well as the lateral measurements and comparing the mean
of the two which should have taken into account any perspective inaccuracies. The
study used a paired t test adopting a significance level of P>0.05.
The study reported that 76% of the horses investigated had a longer right third
metacarpal with three of the right third metacarpals measuring more than 10 mm in
difference, and with 15 horses measuring between five and 9 mm difference with the
right being longer. These are indeed quite large differences, but this may be because
the differences are related to breed and usage, the horses being very young with soft
bones and being exposed to fast work on race courses that involve running on a
circular track. These results in figures reflect the humerus differences in the human
study of Cuk (2001)
David Hall FdSc Dip,WCF Hons April 2013 14
Both papers have slightly different theories as to what causes asymmetry. Cuk et al
(2001) believes that human asymmetry in the upper body (humerous) and the lower
body (femur and tibia) come down to the forces exerted onto the limbs as well as
usage. However (Watson et al 2003) believes that asymmetry of the third metacarpal
is a result of growth process within an individual horse’s skeleton. Cuk et al (2001)
high lights that a factor of asymmetry may also be due to availability of minerals and
vitamins, as well as hormonal regulation, however their experiment concentrates on
forces applied to the limbs along with the usage of the limbs.
Other theories have a part to play in these papers. Steel & Mays (1995) and Cuk et
al (2001) acknowledge that asymmetry can be a result of growth and developing with
age, however in the sense that the older the human becomes, the more usage and
force applied to the limbs. Whereas the Watson et al (2003) paper included theories
that back up asymmetry forming through growth, Kandel et al (1991) reported that
there is asymmetry within the brain, which was proven in great apes, monkeys, cats,
rats and birds. Watson et al (2003) can then refer these results to the horse and
further relate them to the horse’s sidedness, which causes skeletal asymmetry. All of
this occurs without acknowledging extreme usage and forces exerted onto the
different limbs as also reported by Plato et al (1980). These theories are very
different, however both very possible. Cuk et al (2001) and Ruff & Jones (1981)
highlight that they believe that humans develop transverse asymmetry. This is
developed within humans and means that right handed people have a more
developed right arm and left leg, and the reverse in left handed people. Also within
the paper information is given about what Singh (1970); Plato et al (1985) ; Macho
(1991) have all agreed on, which is that the left leg is used as the supportive leg,
without any link too right or left handedness, which then means the right leg is used
for other uses such as kicking.
Cuk et al (2001) do not go into direct detail about how the human is affected by
asymmetry. However, Watson et al (2003) explains that asymmetry between the two
sides of the body may cause trouble with the horses coordination and balance, and
also could be the cause of unilateral injuries. Big asymmetric differences may affect
movement ability along with soundness within the racehorses and turning around the
track.
David Hall FdSc Dip,WCF Hons April 2013 15
Both papers provide results which varied as well as highlighting areas of similarity.
Cuk et al (2001) found that within humans greater asymmetry is found in the upper
body than the lower body, because they found that the arms have a lot more uses.
Humans are also proven in the experiment to be transverse asymmetric, so they
found that right handed people are stronger in the upper half of the body in the right,
and stronger in the left leg for the lower half of the body, then the reverse for left
handed people, which agreed with other studies/theories carried out. However,
regardless to the human’s handedness, the left leg is considered the supportive leg
because it is heavier in the majority of humans and the right leg is used to other
functions. Watson et al (2003) found that the majority of horses (76%) had a longer
right third metacarpal, which was similar to the Meij & Meij (1980) study which
proved 25 out of 30 horses had a stronger hind left limb, which would indicate that
horses with a longer right third metacarpal would also be left hind limb dominant,
showing a connection between humans and horse asymmetry, that being transverse
asymmetry.
2.5 The hoof capsule
In a study by Wilson (2009) into skeletal forelimb measurements and hoof spread in
relation to asymmetry in the bilateral forelimbs of horses. The sample size of 34
leisure horses is an adequate size. No exclusion criteria were mentioned, and no
ethical consent criteria are listed in the paper. There objective was to investigate the
relationship between the morphometry of forelimb segments and hoof spread and
the incidence of asymmetry. 10 bilateral Morphometric measurements of the front
limb were taken four hoof traits and six limb traits were measured. The hoof
measurements were hoof width at the bottom, hoof width at the top, toe height and
heel height. The problem the researcher (Hall) decided with the measurements in
this paper of the hoof width at the bottom, the heel and toe height was it will be
affected by possible outside influences such as inaccurate farriery trimming or
uneven wear. In a pilot study by Caldwell (2012) these measurements were
discounted and the natural coronary band width (CBW) was selected as any
variance in CBW is likely to be bio mechanical influence similar to that of bone
morphology. Wilson’s paper reported no significant difference in the top hoof
measurement between left and right hoof capsules with a mean of 112.1 plus or
minus 11.5 mm in the left capsule and 112.5 plus or minus 11.2 in the right capsule,
David Hall FdSc Dip,WCF Hons April 2013 16
although the range suggests some significant differences at the plus or minus range
between left and right. The limb measurements showed the largest difference with
the measurement at the point of shoulder showing an asymmetry index mean of
12.12mm a range of 0.67-38mm. The statistical test was chi-squared test (X²).
In a pilot study by Caldwell (2012) into hoof volume in the front feet of the horse
amputated at the coronary band, he established a formula for predicting hoof volume
by using the coronary band width. The sample size was 10 pairs of matched feet, so
more of a pilot study. The feet were trimmed to a protocol Caldwell (2010) and
various measurements of a freshly amputated hoof were recorded. The hoof was
then submersed into a displacement tank and the correct volume recorded. The
measurements from the hoof and the known volume calculations were then
processed in mini tab using stepwise regression and a formula that predicted the
volume of the feet was produced. The computer programme picked coronary band
width as the measurement to be multiplied by a constant and divided by a coefficient.
In a study by Decurnex (2009) into different exercise regimes on the proximal hoof
circumference in young thoroughbred horses the author records the decrease in the
circumference of the coronary band as the horse is in training and an increase in
circumference while at rest. The author sites as do many the reason for performing
the study most lameness in horses relates to foot problems and may be associated
with changes in hoof shape, but a lack of information on the influence of normal
exercise on hoof shape. The study was on thirty seven young thoroughbred race
horses, the study lasted sixteen months, thirty two horses managed two consecutive
training periods at the stable separated by a period of rest in a paddock. Five horses
did not complete the second training period. The foot circumference was measured
just below the coronary band weekly with a measuring tape. The study was designed
to test whether proximal hoof circumference was influenced by the type of exercise
accomplished by the horse (gallop training versus rest in the paddock). A one
sample t test was used to evaluate if the mean change per week (during the training
periods as well as during the rest periods) differed from zero. Paired t tests were
used to compare the changes in circumference between the first training period and
the resting period and the change in circumference between first and second training
periods. Most horses showed a similar pattern of change. Decurnex doesn’t really
have an explanation for his findings but does record that the circumference was
David Hall FdSc Dip,WCF Hons April 2013 17
often bigger on the right, the conclusions the researcher draws from this is there is
an inherent asymmetry in these measurements.
2.6 Bio mechanics
In a study by Van Heel (2006) into uneven feet within foals, this may develop as a
consequence of lateral grazing behaviour induced by conformational traits while
foraging. The author of the study questions whether the associated asymmetry will
be linked in the future to loss of performance, injury and future pathology. The study
was on twenty four Warmblood foals born and raised at the same location. There is
no exclusion criteria mentioned in the study and no ethical consent was mentioned.
The foals were visited once a week for an eight hour period by two persons, the
group of twenty four were divided into two groups of twelve and assigned to each
student. The foals were recorded for ten minutes in the hour by scanning the group
and the stance preference if any recorded.
A single tailed t test and regression analysis was used to find that 46% of the foals
developed a significant preference to protract the same limb while grazing which
resulted in uneven feet and subsequently uneven load patterns, with the foot placed
in front having the lowest angle. Foals with long legs and small heads were
predisposed to develop laterality and therefore indirectly cause uneven feet.
In a paper by Scott (2004) Asymmetric limb loading with true or simulated leg length
differences on humans. It is interesting to compare the research on the human leg
length asymmetry with that of the equine, although the research may be different for
the human biped as opposed to the equine which is a quadruped. The paper states
that unequal leg length results in asymmetric limb loading. There is strong evidence
that suggests that musculoskeletal problems of the lower limb and back are
associated with leg length discrepancy. It states that equalising leg lengths to reduce
the incidence of musculoskeletal damage may be warranted, but there are different
opinions regarding the amount of discrepancy that induces abnormal loading and
there is conflicting evidence as to whether the long or the short limb sustains the
greater load, this question of which leg sustains the largest load is present in
debates between clinicians about horses.
David Hall FdSc Dip,WCF Hons April 2013 18
The paper classifies leg length discrepancies as mild (3cm) moderate as (3-6cm)
and severe as more than (6cm), this is indeed extreme compared to the equine
quadruped. The experiment was to calculate symmetry indices from forces seen
during walking on a treadmill between subjects with mild limb length discrepancies
(true leg length discrepancy) and those with a raised shoe, (simulated leg length
discrepancy). There were 8 subjects in the true leg length group and 12 subjects in
the simulated group. All participants signed an ethical consent form that had been
approved by a human subjects institutional review board. Participants were screened
via questionnaire and excluded from the study if they had a history of orthopaedic or
neuromuscular problems other than a leg length discrepancy that might alter their
gait. The results for both the true and simulated leg length achieved by walking on a
treadmill with force plates imbedded showed that all four symmetry indices were
negative denoting higher values for the shorter limb. It states that mechanically
greater loading of the shorter limb would be expected. In transition from stance on
the longer to the shorter limb, the step down distance would be greater than from the
shorter to the longer limb. The peak push off force was greater for the longer leg as
to be expected as it carry the greater lever arm.
2.7 Handedness
In a study by McManus (2009) about the history of human handedness, he states
that about 90% of people are right-handed and 10% are left handed. And that
handedness is associated with functional lateralization for cerebral dominance, and
may also be associated with various types of psychopathology. Broadly speaking,
the vast majority of humans seem to have been right-handed since the emergence of
the genus Homo, some three to four million years ago. Likewise, in all societies
studied, there is a large excess of right-handedness. However, there have been few
studies exploring the detailed history of handedness, not least because adequate
pre-twentieth-century historical data are difficult to find, and very large sample sizes
with consistent measurement methods are required for studies. It is probable that
about 8% to 10% of the population has been left-handed for at least the past
200,000 years or more. Detailed data only began to become available for those born
in the nineteenth century, McManus (2009).
David Hall FdSc Dip,WCF Hons April 2013 19
In a study by Gray (1989) he describes handedness in the equine and compares it to
the humans, outwardly, humans as well as horses tend to appear symmetrical with
respect to left and right, but function is not always symmetrical, especially during
certain phases of movement Steele (2000). This is the result of handedness, an
asymmetrical phenomenon of the brain. The most striking and most fundamental
manifestation of external asymmetry, handedness, is directly linked to brain
lateralization and is described as the "physical manifestation of brain laterality."
He states that the "split" or "dual hemisphere" type of brain is a characteristic
common to vertebrates. The left and right hemispheres interact and work together to
handle the complex tasks of analyzing and organizing thought processes and
directing physical activities and body functions. Laterality or Lateralization is the
neuropsychological term used to describe the division of labour between the two
brain halves of what is commonly referred to as the "split brain."Diagonal orientation
and handedness in the case of horse’s sidedness, resulting in lateralisation help to
understand the asymmetrical behaviour of horses. The study observed over five
hundred horses and his preliminary findings were that approximately 75% of the
animals studied displayed a preference for the left lead, which would indicate a
dominant diagonal consisting of the right hind/left fore (right sided). The number of
animals that displayed extreme ambidextrous tendencies was 3, less than 1%. The
number of animals showing sided tendencies, to such a degree, that one or more
limbs were showing obvious but tolerable signs of stress from weight bearing
imbalances was over 60%. Methods used to bring about improved locomotive and
weight-bearing balance included shoeing techniques which considered natural
asymmetrical tendencies, balanced riding techniques and therapeutic exercise.
These observations were not presented in a scientific format but were in accordance
with other authors and a pilot study by Caldwell (2012). Gray subscribes to the
theory that horses are inherently asymmetric and this wasn’t acquired, the horse was
actually born with theses tendencies.
David Hall FdSc Dip,WCF Hons April 2013 20
Chapter 3 methodology
3.1 Introduction
This chapter sets out to describe the research methodology and design. Research
methodology is defined in simple terms as being a system of models, procedures
and techniques, which are used to find the results of a particular research problem
Panneerselvam (2004). Research techniques can be categorised into two sections
quantitative and qualitative or both can be used in mixed research methods Gray
(2010).
It has been described that quantitative research deals with quantity or numbers
whereas qualitative research, with quality and description of the subject being
researched, this summary however, is simplistic and distinguishing between the
paradigms can be problematic Parahoo (2006).
3.2 Aims of the study
The aim of this pilot study of a group of freshly amputated limbs was to record the
physical measurements of the length of the third metacarpal from the proximal
extremity at the point where the facet in the joint for the 4 th and 5th carpal bones sit
and at the distal extremity of the sagittal ridge at the lowest point of its radius.
Measurements of the mid shaft circumference and the mid shaft width were also
taken and recorded. The coronary band width was measured to see if there is a
correlation between the third metacarpal dimensions and coronary band width.
.
3.3 Hypothesis
There is a considerable volume of anecdotal evidence to suggest that miss matched
feet are linked to differential leg length syndrome (DLLS) and that DDSL is common
in domesticated horses, other terms for this condition are limb length disparity, odd
or uneven limb length.
There are differences between left and right coronary band widths, but there is no
difference in right and left metacarpal length, width or circumference. Therefore
differential leg length syndrome (DLLS) can not be linked to mismatched feet.
David Hall FdSc Dip,WCF Hons April 2013 21
3.4 Experimental design
To establish if differences between left and right coronary band widths exist and if
there is a correlation between coronary band width differences and differences in
either length or circumference or width of the third metacarpal
We hypothesise that differences between left and right coronary band width exists,
but that there is no difference in right and left metacarpal length or circumference
therefore DLLS can not be linked to mismatched feet.
The experiment on 15 pairs of freshly amputated front limbs from 15 horses
euthanized for other reasons at a hunt kennels. The limbs were removed at the
carpus soon after death and stored in a cooler at two degrees centigrade until
sufficient limbs for the experiment had been gathered. The legs were examined to
make sure that they were free of damage from the euthanasia process, in all the
horses used in this experiment shooting was the method used to destroy the animal,
and not damaged in the amputation process. If any damage was encountered that
would affect the measurement process then they were excluded from the study. The
experiment was conducted on the hunt premises as moving the limbs would require
a licence.
3.5 Ethical consideration
Ethical consent was sought and granted from Myerscough college ethics committee
to conduct the experiment. The experiment met the strict guidelines set out by the
licensing laws for the movement and control of fallen stock, the amputated limbs fell
into this criteria. The experiment was to be carried out on a licensed premises with
written consent from the senior huntsman at the kennels and the limbs to be
disposed of immediately afterwards through the hunts disposal methods. Client
confidentiality was a major consideration, as the destruction of someone’s horse is a
sensitive matter. All data was stored on a computer hard drive with password
security.
3.6 objectives of the research
The objective of this research is to provide quantitative measurements that show the
possible components that make up the asymmetry or limb length disparity in the fore
David Hall FdSc Dip,WCF Hons April 2013 22
limbs of the front legs of the horse. The other objective is to see if there is a link with
the observable asymmetry in the fore feet where the coronary band is narrower in
one foot compared to the contra lateral foot. The foot is a complex shape and
doesn’t fit any particular geometric shape. The nearest shape it comes to is an
incomplete cone.
There are many areas that one hoof can be directly compared to another and
measurements of all areas could be considered as comparative.
Establishing measurements that are not effected by outside influences will be
desirable Turner (1992). Influences that may effect will be farriery, the removal of
horn through trimming or burning. Farrier protocols have an inherent inaccuracy. For
example if the heel height differences were to be considered, one heel being higher
in one foot than the other, is this a result of inaccurate farriery or a morphology of the
capsule. In a study by Caldwell (2010) a trimming protocol was designed, but when
measuring for differences between feet the farrier will have an influence on these.
When visually assessing feet, the appearance of a difference in width at the proximal
aspect of the hoof can be observed. This observable capsule distortion is usually in
conjunction with other easily observable other factors within the limb this includes
high and low heels Van Heel (2006), Ridgway (2010), difference in distal radius
height Caldwell et al (2010) and position differences in the scapular position Buff et
al (2008)
In a pilot study by Caldwell et al (2012), the distal radius height was measured using
a laser level and a comparison done between left and right fore limb. While
performing this study the coronary band width was recorded. In 75% of those
measured there was a difference in radial height, where the distal radius was higher
the coronary band width was narrower. Where the distal radius was lower then the
coronary band was wider.
The coronary band was measured using an Invictor calliper in this experiment at the
widest part of the proximal capsule 10mm below the hairline on both fore feet.
The differences in measurement between the coronary band widths were not great.
The shape however of the proximal border was elongated and made easier to
observe.
David Hall FdSc Dip,WCF Hons April 2013 23
Fig 3.1 Distal radius height is pin pointed by a laser level, by highlighting this
anatomical feature, limb length asymmetry is then easily observed.
Fig 3.2 This photo shows the experiment being under taken using the laser level.
By conducting this experiment it established that the position of the distal radius was
often at a different height in left and right.
The factors that could cause this would be a longer limb, a more obtuse angle in the
scapular humerous joint Buff et al (2008), an increased palmer angle Clayton (1990)
and shortening of the deep digital flexor tendon Redden (2003) or a longer third
metacarpal Watson (2003), or a combination of all three and other yet unexplored
factors. This was the reason for measuring the length of the third metacarpal.
David Hall FdSc Dip,WCF Hons April 2013 24
To measure the third metacarpal it was decided to measure from the dorso proximal
point between the joint facet of the 4th and 5th carpal bones to the most distal point of
the median ridge. This will effectively be the longest measurement of the long bone.
3.7 Experimental procedure
The amputated limbs were examined for damage sustained in the euthanasia or
amputation, fifteen pairs were accepted and eight pairs were rejected because of
joint surface damage during the amputation or dissection process. The coronary
band width was measured using an Invictor calliper at the widest part of the hoof
10mms below the coronary band. This measurement was alternated between left
and right feet and repeated three times. Each of the measurements was verified by
operator and an assistant and recorded in a note book for transference to a table
later.
The limb was then dissected removing the third metacarpal in its entirety including
the second and fourth metacarpals still attached. Any parts of the limb below the
meta-carpo phalangeal joint, that included the proximal and the middle phalanx and
the hoof capsule which were discarded at this point. Owing to ossification of the
interosseous ligament between the second and fourth metacarpals to the large
metacarpal separation of these bones was very difficult without damaging the bones;
this is common in mature horses. It was decided to measure the shaft region with
them still attached.
The third metacarpal was measured using an Invictor calliper from the dorso
proximal point between the joint facet of the 4 th and 5th carpal bones as in fig3.3 to
the most distal point of the median ridge.
David Hall FdSc Dip,WCF Hons April 2013 25
Fig 3.3
These measurements were verified by the operator and assistant, collected and
recorded in a note book for transference to a table at a later date.
The third metacarpal mid shaft width was calculated by dividing the overall length in
half and a mark placed on the bone with a permanent marker equidistant from the
proximal and distal extremities. This width measurement was taken from the medial
to the lateral extremities at this mid point using an Invictor calliper. Each
measurement was taken three times by the operator and verified by an assistant and
entered into a note book.
The third metacarpal mid shaft circumference was measured using a tailors tape at
the mark defined as the middle of the shaft equidistant from either extremity. Again
all measurements were recorded three times and verified by an assistant.
3.8 Data collection
Forty five figures were recorded for each measurement (15 pairs of limbs each
measurement measured three times) for both the left and right third metacarpals and
left and right coronary band widths. In order to standardise the measurements the
mean for the three measurements was calculated and entered into a Microsoft excel
spread sheet. The table consisted of 15 measurements for left metacarpal length
and fifteen for the right, fifteen measurements for the left metacarpal width and
David Hall FdSc Dip,WCF Hons April 2013 26
fifteen for the right and fifteen measurements for the metacarpal mid shaft
circumference left and right. The left and right coronary band measurements fifteen
of each were also entered into the excel chart.
3.9 Data analysis
Statistical analysis is required to standardise the raw data, for this a student’s paired
t test is used, for this the number of points in each data set must be the same, and
they must be organized in pairs, in which there is a definite relationship between
each pair of data points. The coloration between the data set is calculated using a
Pearson's correlation coefficient. If it is believed that there is a linear relationship
between two quantitative variables with a change in one variable being associated
with a change in the other then Pearson’s correlation is used. The degree of
association is calculated Pearson’s product moment correlation coefficient can take
any value between -1 and +1 and expressed as r. It is said that there is a perfect
correlation if all the points lie on the line (XY) the value of the coefficient takes one of
its extreme values, either +1or-1. In order to establish a relationship we have a
positive correlation if the sign of the correlation is positive; then there is a direct
relationship between two variables so that as one variable increases in value so
does the other variable. If r has a negative correlation if the sign is of the correlation
is negative; then there is an inverse relationship between the two variables so that as
one variable increases in value, the value of the other decreases. To relate this to
our experiment if the probability value is p> 0.05 and r= 0.8 or above then it would
suggest there is a positive correlation between the two sets of data.
3.10 Procedural check list
1) The freshly amputated limbs will be skinned using a boning knife and the third
metacarpal removed in both left and right front limbs.
2) Using a sliding calliper the third metacarpal is measured in length from the
point on the most proximal dorsal facet as in fig 9 to the longest point on the
Median Ridge as in fig 10. Further measurements will be taken from the same
David Hall FdSc Dip,WCF Hons April 2013 27
point on the Carpus to the extremity of the medial condoyle and then to the
same point on the lateral condoyle.
3) The mid shaft position is determined by dividing the length in half and a
permanent marker used to mark this point.
4) The width of the M3 will be measured medially-laterally at the mid shaft also
using a sliding calliper at the point marked.
5) The circumference of the third metacarpal is measured using a tailors tape at
mid shaft.
6) The measurements will be recorded in table form for later analysis and left
compared to right for differences.
7) The hoof capsule will be measured using a sliding calliper 10mm below the
hair line at the widest part of the hoof fig 11.
8) The hoof capsule measurements will be recorded in table form and left
compared to right.
9) Using data analysis the incidence of asymmetry in the right and left third
metacarpal will be ascertained and then compared by statistical analysis to
the asymmetry between left and right fore feet coronary band width to see if
there is a relationship.
Ethical consent
Ethical permission was sort to conduct this experiment. It was required
because the handling and moving of the morbid specimens is a licensed
operation.
The study did not identify the components that contribute to the asymmetry but
identified that it existed. As previously stated in Dollar (1898) that bone length and
the angles that they make with each other that a new study where matched bones
from morbid specimens could be measured this theory could be checked.
David Hall FdSc Dip,WCF Hons April 2013 28
Chapter 4 - Results
4.1 group demography
The study sample consisted of 15 pairs of limbs amputated below the carpus joint.
The horses were of a mature but mixed age, size and type. No descriptive data was
recorded for the horses prior to being euthanized.
4.2Table of results of raw data
Key: CBW- Coronary Band Width; MCL- Metacarpal Length; MCW- Metacarpal Width;
MMSC- Metacarpal Mid-Shaft Circumference
Horse
s 115
Horse
1
Horse
2
Horse
3
Horse
4
Horse
5
Horse
6
Horse
7
Horse
8
Horse
9
Horse
10
Horse
11
Horse
12
Horse
13
Horse
14
Horse
15
CBW
(mm)
(Left)
CBW
(mm)
(Right)
MCL
(mm)
(Left)
MCL
(mm)
(Right)
MCW
(mm)
(Left)
MCW
(mm)
(Right)
MMSC
(mm)
(Left)
MMSC
(mm)
(Right)
116
115
272
272
43
43
127
125.5
115
115
258
258
39
39
118
112.7
129
129
259.3
260
44
44.7
126.3
126.3
115
114
286.3
286.7
41
40
125
123.7
114
115
280
278
40
39
120.3
119
108
104
281
279
37
37.17
105
107
111
105
279.3
279
42.17
41
118.3
116
117
121
281
279.7
40.83
40
118
116.7
107
102
278
277
41.3
39.7
117.7
115
112
110
281.3
280
41
40
117.7
116.7
110
108
287.3
286.3
39
39
114.3
113
112
113
253.7
253
40.3
38.3
117
112.7
135
136
280
277.7
46.3
46.7
134.7
134.3
111
113
274
275
38
39
120
117.3
106
105
256.7
255.3
36
35
111.7
110.3
Table 4.1 – Full results of all the horses studied.
David Hall FdSc Dip,WCF Hons April 2013 29
CBW
(mm)
MCL (mm)
MCW
(mm)
MMSC
(mm)
MEAN
LEFT
(mm)
MEAN
RIGHT
(MM)
PAIRED
value
114 ± 7.9
274 ± 11.3
114 ± 9.
273 ± 11
p>0.05
p>0.05
41 ± 2.7
40 ± 2.9
p>0.05
119 ± 7
118 ± 7
p>0.05
"T"
P
Table 4.2 research descriptive statistics. There are no significant
differences between left and right limb variables p>0.05
4.3 discussion of results on raw data
Metacarpal length was longer in left limb in 10 (67%) of the limbs
measured, 3 (20%) in the right and equal in 2 (13%). The differences were
very small and deemed not significant when viewed as a percentage of the
whole length. Metacarpal width was wider in the left limb in 8 (53%) of the
limbs measured, 4 (27%) in the right and equal in 3 (20%).
Metacarpal mid shaft circumference was greater in the left limb measured
in 13 (86%) of the limbs measured, 1 (7%) in the right and equal in 1 (7%).
As mentioned before the result’s shows a small difference in metacarpal
length this would be in accordance with the researcher’s previous studies.
The mean of the left third metacarpal length being 274mm+/-11.3mm and
the mean of the right third metacarpal being 273mm+/-11mm p>0.05.The
asymmetry in the third metacarpal length does exist but in small
proportions. There is a greater degree of asymmetry in the width and
circumference of the third metacarpal although still small. The third
metacarpal width at the mid shaft of the long bone on the left had a mean
of 41mm +/-2.7mm and on the right 40mm +/- 2.9mm p> 0.05. The mean
for the mid shaft circumference on the left 119mm +/-7mm and on the right
David Hall FdSc Dip,WCF Hons April 2013 30
118 mm +/- 7mm.
The coronary band for the left hoof capsule was wider in 8 (53%) of the
limbs measured, 5 (33%) in the right and equal 2 (13%). The coronary
band width had a mean of 114 mm +/- 7.9 mm on the left and 114 mm +/- 9
mm 0n the left.
4.4 statistical analysis of data
All the measurements coronary band width, metacarpal length metacarpal
width and metacarpal circumference were transferred to Microsoft excel
2010® for statistical analysis. Descriptive data were generated using
analysis tool pack Visual Basis for Application VBA. Pictorial analysis of
correlations was performed using scatter graphs generated within excel
graphs manager® with trends and standard error and or deviations added
using layout tools within the data analysis software. Relationships were
tested using fielders “F” test for equal variance followed by two sided
student t test with either equal or unequal variances as appropriate and at
confidence intervals of 0.95. The researcher then used paired t test, and
Correlations were calculated using Pearson’s correlation and tables of
critical values at N-2 DF (degrees of freedom) to determine if there was a
relationship between any of the three bone measurements with the
coronary band width.
4.5 metacarpal length
There was no difference in the length of the third metacarpal, statistically
no difference using the paired t test. Using the Pearson correlation test
there was no correlation found with coronary band width and metacarpal
length. R=0.717 p>-0.102 for the right limb and a minus p value for the left
R =0.876 p-0.044.
4.6 metacarpal width
In the paired t test there was no significant difference between third
metacarpal width in left or right fore limbs.
David Hall FdSc Dip,WCF Hons April 2013 31
n
Mean(mm)
St Dev
SE Mean
CBW(Left)
15
114.53
7.87
2.03
CBW(Right)
15
113.67
9.33
2.41
difference
15
0.867
2.669
0.689
Table 4.3 shows the mean, standard deviation and standard error for
CBW.
There is a 95% confidence interval for a mean difference: (-0.611,2.345)
T-test of mean difference= 0 (vs not = 0) : T-value = 1.26 P value = 0.229
There was a strong relationship with third metacarpal width and coronary
band width when compared in a Pearson correlation test. R=0.819 p>0.05
for the left and R=0.784 p>0.05 for the right.
4.7 metacarpal mid shaft circumference
There was more significant difference between third metacarpal mid shaft
circumference in a paired t test between left and right forelimbs.
N
Mean (MM)
St Dev (MM) SE
Mean
(MM)
MMSC (Left)
15
119.40
6.98
1.80
MMSC
15
117.75
7.08
1.83
15
1.653
1.723
0.445
(Right)
Difference
Table 4.4 shows the mean, standard deviation and standard error for
Metacarpal Mid-Shaft Circumference.
There is a 95% confidence interval for the mean difference: (0.669, 2.608)
David Hall FdSc Dip,WCF Hons April 2013 32
T-test of mean difference = 0 (vs not =0) : T-value = 3.72 P-value = 0.02.
There was a strong relationship with third metacarpal mid shaft
circumference with coronary band width in a Pearson correlation test.
R=0.089 p>0.05 with the left limb and R=0.811 p0.05 for the right.
There is a strong statistical relationship between coronary band width, and
metacarpal mid shaft circumference and third metacarpal width. This would
be expected as when the width increases it would be expected to show an
increase in circumference.
When the means between the four measurements (metacarpal length,
metacarpal width, metacarpal mid centre circumference and coronary band
width) are compared they all show a larger mean for the left fore limb than
the right. This is comparative with other studies performed.
We have already shown a significant linear relationship between
metacarpal mid shaft circumference and coronary band width r = 0.81 p =
0.044. Metacarpal mid shaft circumference was greater in the left limb
measured in 13 (86%) of our sample pairs. We could not find evidence of
sufficient strength to suggest correlations between any of the variables in
our sample.
Accordingly at this time we must reject the null hypothesis of a significant
difference existing between key measures of left and right metacarpal. We
find we are also unable to accept the hypothesis of no difference of key left
/ right variables at this time without speculating as to the causes, further
work is needed.
A power calculation subsequently run in Minitab 16® suggests that an
increase in sample size in the magnitude of 50 would give a CI in the
region of 0.95.
David Hall FdSc Dip,WCF Hons April 2013 33
LEFT RIGHT MEASUREMENT (MM)
300.00
250.00
200.00
150.00
100.00
50.00
0.00
CBW (Left)
CBW (Right)
MCL (Left)
MCL (Right)
MCW (Left)
MCW (Right)
MMSC (Left)
MMSC (Right)
Figure 4.1 highlights the difference between left and right variables, including the
error bars and the standard deviation bar. There are no significant differences
p>0.05.
140
135
130
R² = 0.6589
MMSC (mm)
125
120
115
110
CBW
105
100
95
fig 2
90
100
105
110
115
120
125
130
135
140
CBW (mm)
Figure 4.2 this scatter graph illustrates the strong correlation found between the
coronary band width and metacarpal circumference r=0.812 p=0.044. R has been
squared to normalise the distribution.
David Hall FdSc Dip,WCF Hons April 2013 34
MMSC Line Fit Plot
140
135
130
125
CBW
120
115
CBW
110
Predicted CBW
105
100
fig 3
95
90
100
110
120
130
140
MMSC (mm)
Figure 4.3 fitted line plot highlights the correlation between MMSC and CBW. The
data shows a strong linear relationship p<0.05
R=0.812
P=0.044
coronary band width & metacarple
circumferance Left - Right difference
8
6
4
2
0
0
2
4
6
8
10
12
14
16
-2
-4
-6
MMSC L - R
CBW L - R
limb pairs ranked bt difference L-R.
Figure 4.4 this scatter graph demonstrates a strong relationship between coronary
band width and Metacarpal circumference.
David Hall FdSc Dip,WCF Hons April 2013 35
Chapter 5 discussion
Metacarpal asymmetry 5.1
The asymmetry that exists in the third metacarpal is less present in bone length and
more pronounced in mid shaft circumference and mid shaft width, although the width
as stated earlier will be related to an increase in circumference.
These findings match the anthropology studies Cuk (2001) of the femur of the
medieval skeletons. In that study the author finds that the largest asymmetry in
length of the long bone occurs in the right humerous of the human, it states that the
reason for that is the multi-directional function of the arm. The equine does not have
that range of movement in the fore leg that is present the upper arm of the human. It
is more in keeping with the femur of the human and as Cuk (2001) reports the same
increase in width and circumference and minimal difference in length as the
researcher has found in the third metacarpal.
Coronary band width 5.2
The differences in coronary band widths were smaller in this study than the
researcher has experienced in previous studies although still different. Previous
studies have been on live horses still weight bearing on the capsules being
measured. In the study performed in coronary band circumference on Australian
race horse horses Decurnex (2009) reported of the fluctuation in circumference
increasing while the horse is in training and decreasing while the horse is at grass. In
the time between euthanasia, amputation and measurement it may be while
unloaded the coronary band width contracts on the wider foot in the researcher’s
morbid specimens.
5.3 Relationship between coronary band width and third metacarpal length.
There is a strong statistical relationship between coronary band width, metacarpal
mid shaft circumference, third metacarpal width and metacarpal length. When the
David Hall FdSc Dip,WCF Hons April 2013 36
means between the four measurements are compared they all show a larger mean
for the left fore limb than the right. This is comparative with other studies performed.
These results are not confined to the equine only they are reflective of results in
humans as well Cuk (2001). The results are similar to handedness and preferred
lead studies carried out Van Heel (2006), Gray (1989). The increase in bone
measurements like that of the coronary band likely to be larger because of increased
pressure from descending body weight more pronounced on one side (the left). In a
previous study by Hall (2010) on distal radius height the distal radius height
measured higher on the right limb in 75% of the horses measured, this linked to this
study may suggest a step down effect reported in White (2004) This would cause
increase in pressure likely to cause an increase in coronary band width and increase
in bone density.
It can be suggested that the measurement differences are small as larger differences
would interfere with the bio-mechanical functions of the quadruped. The visible
differences reported Dollar (1898) in limb asymmetry is likely to be the angle the
bones make with each other rather than length.
The existence of front limb asymmetry in various forms is not in dispute. In a recent
pilot by Caldwell (2012) it was identified limb length disparity existed. Using external
markers on given reference points of the horse, Weller (2006) the horse was
photographed. Using computer analysis the distance between the markers and the
angles were recorded and compared between right and left side of the horse. The
study showed that in the small study that 75% of the horses demonstrated fore limb
asymmetry. The study did not identify the components that contribute to the
asymmetry but identified that it existed. As previously stated in Dollar (1898) that
bone length and the angles that they make with each other that a new study where
matched bones from morbid specimens could be measured this theory could be
checked.
David Hall FdSc Dip,WCF Hons April 2013 37
Fig 5.1 These images show external reference markers placed on a horse and
computer analysis to plot the distance and angles to demonstrate asymmetry.
5.4 Limitations of the study
The lack of available research prior to this study makes it difficult to compare the
findings or how the experiments were performed. The fact the data was recorded on
cadaver limbs makes it difficult to compare the findings against the live equine.
Although it could be suggested that radiographs of the third metacarpal would
provide a linear measurement of asymmetry providing there was suitable calibration
for measurement. Measurements which are taken using an invicta calliper leave the
results open to individual bias or interpretation, which is why it is vital that external
researchers sample the data to ensure accuracy. A possible suggestion to overcome
this would be to photograph the bones and hooves and measure the linear lengths
and widths using digital measurement software providing there is suitable calibration.
Chapter 6 Conclusion
There were small differences measured in the length of the third metacarpal between
right and left bones. In this sample size the differences were not deemed as
statistically significant. However in a larger sample size it may be the small
differences have more significance, so it is not possible to say there is a relationship
between coronary band width and metacarpal length.
There is however a strong statistical relationship between third metacarpal
circumference and coronary band width, this would suggest that the asymmetry is
David Hall FdSc Dip,WCF Hons April 2013 38
linked to bio mechanical forces on the limb similar to skeletal changes linked to
handedness.
Chapter 7 clinical relevance
7.1 Clinical relevance of the asymmetry
There has been much speculation on the existence of limb length disparity, unequal
leg length and differential leg syndrome and it is easily observed when viewing the
fore limbs in the equine. Much is spoken by the people involved in the performance
criteria of the horses and the consequences of an asymmetric horse as to whether it
is performance inhibiting and indeed if on pre purchase examinations from the
veterinary surgeons should the difference be treated as an unsoundness. Without full
knowledge of the constituents that go to make up the asymmetry and there links to
equine biomechanical lameness, Rooney (1968) then deciding if the condition is
linked with future pathology would be difficult.
With the discovery that the bone length of the third metacarpals, are not significantly
different then the asymmetry lies elsewhere, this may mean that different types of
asymmetry will be acquired or cured depending on environmental conditions
management and equine well being. This will explain that the appearance of some
types of asymmetry within the fore limb seeming to worsen or improve. Had it been
linked to unequal bone length then this fluctuation would be less likely to be
observed.
7.2 Asymmetry in the hoof shape
The researcher has concluded that the difference in hoof shape is reflective of
weight bearing pressure and handedness. The hoof, as stated before, on the
narrower coronary band width and elongated proximal shape has other
commonalities that lead the researcher to this conclusion. The measurements of the
coronary band width has a strong relationship with metacarpal circumference, in
studies previous to this pilot study the increase in long bone development is
suggestive of repetitive increase in load as would the deformation of the hoof
capsule, the increase in coronary band width being related to increase in metacarpal
circumference as in the Wilson (2009). The associated structures that would either
be related or the cause of the differing coronary band width would be the angle that
David Hall FdSc Dip,WCF Hons April 2013 39
P3 occupies within the hoof capsule, Redden (2003), Moleman (2005) and the
contracture of the flexor tendons and or contracture of the muscles involved in there
operation Redden (2010)
References:
Cuk, T,. Leben-Seljak, P,. Stefancic, M,. (2001) 'Lateral Asymmetry of Human Long
Bones' Variability and Evolution, Vol. 9, pp19-32
Caldwell, M,. Hall, D,. Jerram, M,. Young, A,. Reilly, J.D,.(2012) 'The relationship of
limb length disparity, preferred lead and stride length with hoof capsule Asymmetry
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David Hall FdSc Dip,WCF Hons April 2013 43
Appendices letter of consent from the hunt kennels for carrying out the experiment
on there premises.
David Hall FdSc Dip,WCF Hons April 2013 44
David Hall FdSc Dip,WCF Hons April 2013 45