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.
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 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.
Contents Page
Title pagePage 1
AcknowledgementsPage 2
AbstractPage 3
Table of contentsPage 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
Chapter 3 – Methodology Page 21
3.1Introduction 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 Page 36
5.1 Metacarpal Asymmetry Page 36
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 ListPage 40
Bibliography Page 43
Appendices Page 44
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 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 ashoof 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.
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 carpiradialis 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 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 impactas 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).
Fig1.1 A diagram of the hoof function underload, 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.
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. 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 contra-lateral 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)
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) highlights 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.