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This is to certify that the
thesis entitled

THE APPLICATION OF THREE-DIMENSIONAL
KINEMATIC METHODOLOGY TO THE EQUINE KNEE
AND ANKLE JOINTS

presented by

Camie Renee Heleski

has been accepted towards fulfillment
of the requirements for

Master of Science degree in Animal Science

    

Major professor

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THE APPLICATION OF THREE-DIMENSIONAL
KINEMATIC METHODOLOGY TO THE EQUINE KNEE
AND ANKLE JOINTS

By

Camie Renee Heleski

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Animal Science

1991

(5145/0

ABSTRACT
THE APPLICATION OF THREE-DIMENSIONAL

KINEMATIC METHODOLOGY TO THE EQUINE KNEE
AND ANKLE JOINTS

BY

Camie Renee Heleski

Three-dimensional videography and computer modelling were
used to analyze flexion/extension, abduction/adduction, and
internal/external rotation of the equine knee and ankle. The
left knee and ankle of two "normal" (non-pathological) Arabian
fillies were analyzed and evaluated during standing, walking,
and trotting. Methodology similar to that used in human
studies was applied. The forearm, cannon, and pastern were
modelled as rigid bodies. Three, non-collinear targets were
positioned on each rigid body. Four video cameras were set up
in an arc around the level treadmill upon which the subjects
were filmed. A previously written motion analysis computer
package was used to analyze the data. Joint coordinate
analysis programs were adapted from human research. After the
data were plotted, curve shapes were compared and found to be
similar from trial to trial within each horse. Basic curve
shapes were similar, but differed in magnitude, between the
subjects.

ACKNOWLEDGEMENTS

First, I would like to thank my graduate committee: Dr.
Duane Ullrey, Dr. Robert Soutas-Little, and Dr. Ted Ferris,
for their patience, support, and assistance in completing this
project. They believed in me and gave me very helpful advice.

A special thank you to my major professor, Dr. John
Shelle. His friendship, support, and willingness to tread new
ground were greatly appreciated, as were the hours he spent
shaping my thinking and reasoning skills.

I am eternally grateful to Dr. Soutas-Little, Dr. Charlie
DeCamp, and the entire staff of the Human and Veterinary
Biomechanics Evaluation Laboratories. These people all went
above and beyond the call of duty to assist me with my project
and to share their technology.

I am also indebted to Dr. John Stick for allowing me to
use the treadmill at the Equine Performance Center and
providing one of his technicians, Troy Trumbul, for the test
date. In addition, Paula Fulkerson and her staff at the Horse
Teaching and Research Center were instrumental in assisting me
with the horses.

A blanket thanks goes to my office-mates and all the

other graduate students, faculty, and staff who helped inspire

iii

me, teach me, and provide friendship during my master's
program.

Finally, I would like to extend grateful acknowledgement
to my husband, Ernie, my family, and God for giving me the
moral stamina to complete this endeavor. I would not be at

this point without them.

iv

TABLE OF CONTENTS

ListofTables.............................................vi
ListofFigures...........................................vii
Introduction................................................1
ReviewofLiterature........................................2
MaterialsandMethods......................................20
ResultsandDiscussion.....................................40
Conclusion.................................................69
Appendix...................................................71

ListOfReferenceSOOOOOOOOO0.00.00.00.00.0.0.0.00000000000077

TABLE 1.

Environment

LIST OF TABLES

29

LIST OF FIGURES

FIGURE 1. Lateral view of the left, lower leg showing
targeting scheme and coordinate systems. 22

FIGURE 2. Calibration structure, showing calibrated
volume and the sixteen coordinate points. 25

FIGURE 3. Overhead view of the calibrated space in
relation to the treadmill, and the position of the
cameras. 27

FIGURE 4. Sample mergers in the data which were deleted
using the "Mask" program within the EV3D program. 30

FIGURE 5. The "Track" program within EV3D showing the
50th frame of data as seen from each camera view. 31

FIGURE 6. "Track Edit" program within EV3D, demonstrating
changes in the x, y, and z trajectories of target 1. 33

FIGURE 7. Stick diagram of one complete gait cycle.

Arrows indicate direction of the gait cycle; the area

between hoof strike and toe off represents stance phase:

the remainder of the cycle comprises swing phase. 34

FIGURE 8. Changes in the angle created by targets 7, 8,
and 9. The changes appeared to be based on calculated
centroid changes. 36

FIGURE 9. Joint coordinate system for motions of the knee.
Motions are of the distal segment relative to the proximal
segment (lateral view of left leg). 37

FIGURE 10. Joint coordinate system for motions of the
ankle. Motions are of the distal segment relative to the
proximal segment (lateral view of left leg). 38

FIGURE 11. EV3D generated flexion/extension curve of
subject BS's knee while trotting. Peak areas represent
maximum flexion. Low areas represent stance phase. 41

FIGURE 12. EV3D generated flexion/extension curve of

subject BS's ankle while trotting. Peak areas represent
maximum flexion. Low areas represent stance phase. 42

vii

FIGURE 13. A sample walking trial examined with stick

figures in one gait cycle, and then broken down by time.

These types of figures helped identify hoof strike and

toe off. 44

FIGURE 14. Kinematics for the knee joint. "Abd+" means
abduction occurs in the positive direction; "Add-" means
adduction occurs in the negative direction. "Flex+" means
flexion occurs in the positive direction; "Ext-" means
extension occurs in the negative direction. "IntR+" means
internal rotation occurs in the positive direction; "ExtR—"
means external rotation occurs in the negative direction. 46

FIGURE 15. Kinematics for the ankle joint. Slight
deviations in the standing data are due to the subject
shifting weight. 47

FIGURE 16. Kinematics for the knee joint. The legend is

the same as that described in Figure 14 with the addition of
hoof strike (labelled heel strike) and toe off being marked in
the first gait cycle. Also, "F/E - Standing" gives the
average standing value for flexion/extension. 48

FIGURE 17. Kinematics for the ankle joint. The legend is
further described in Figures 14 and 16. The first peak of
flexion is referred to as "a". The second peak of flexion is
referred to as "b". 49

FIGURE 18. Kinematics of the knee joint. The legend is
further described in Figures 14 and 16. Each trial
represented was chosen as being exemplary of the three

trials filmed for each particular condition. 51

FIGURE 19. Descriptive drawings of the motions being
described. 52

FIGURE 20. Kinematics of the ankle joint. The legend is
further described in Figures 14 and 17. 53

FIGURE 21. Kinematics for the knee joint. See Figure 14
for further explanation of the legend. 57

FIGURE 22. Kinematics for the ankle joint. See Figure 14
for further explanation of the legend. 58

FIGURE 23. Kinematics for the knee joint. The legend is
further described in Figures 14 and 16. 59

FIGURE 24. Kinematics for the ankle joint. See Figures 14 ,
and 17 for further explanation of the legend. 60

FIGURE 25. Kinematics for the knee joint. See Figures 14
and 16 for further explanation of the legend. 61

viii

FIGURE 26. Kinematics for the ankle joint. See Figures
14 and 17 for further explanation of the legend.

FIGURE 27. Cross plot of knee against ankle flexion/
extension. The direction of motion is counter-clockwise.
This plot is for Subject 88 while walking.

FIGURE 28. Cross plot of knee against ankle flexion/
extension. The direction of motion is counter-clockwise.
This plot is for Subject BS while trotting.

FIGURE 29. Cross plot of knee against ankle flexion/
extension. The direction of motion is counter-clockwise.
This plot is for Subject EC while walking.

FIGURE 30. Cross plot of knee against ankle flexion/

extension. The direction of motion is counter-clockwise.
This plot is for Subject EC while trotting.

ix

62

65

66

67

68

INTRODUCTION

Despite a historic interest in analyzing equine
locomotion, studies of which date back to the 1600's (Leach
and Dagg, 1983a), there is a paucity of scientific literature
to substantiate hypotheses concerning equine gait. In view of
the potential applications for biomechanics in the growing
horse industry, this lack of documented research is
disturbing. Potential applications range from more accurate
lameness diagnosis, to more appropriate corrective shoeing
methods, from selecting athletes of the highest potential, to
optimizing racetrack conditions (Leach and Dagg, 1983b).

Three-dimensional analyses have rapidly expanded the
study of human biomechanics (Ulibarri et al., 1987). In light
of this expansion, there is much potential for the impact
three-dimensional analyses may have on explicating equine
gait.

Due to the perceived need for more accurate information
about equine gait analysis, this pilot study was undertaken to
develop the methodology for three-dimensional kinematic data
collection and analysis of the knee and ankle. This study was
concerned with examining the flexion/extension,
abduction/adduction, and internal/external rotation patterns
which occur in the horse's knee and ankle. Three-dimensional

data derived from high speed video films and analyzed using

2
joint coordinate analysis provided more complete information
than have previous two-dimensional analyses, which have
typically examined only the sagittal plane of motion.

The primary purpose of this study was not to establish a
statistically significant base of knowledge of what "normal”
knee and ankle kinematics are, but, rather, to develop a
workable three-dimensional methodology to lay the foundation
for future equine kinematic studies. It is hoped that after
more work is done in identifying "normal" kinematic patterns
in the knee and ankle, that work will proceed on more clearly
identifying elusive lamenesses. JHopefully, studies will also
commence on evaluating the effects of corrective trimming and
shoeing. Similar methodology to that used in this study
should also be applicable to other joints of the horse's body,
such as the hock and stifle.

REVIEW OF LITERATURE

The study of biomechanics has appealed to researchers for
centuries. .Aristotle made general observations of locomotion
patterns in quadrupeds during the Fourth Century B.C. (Smith
and Ross, 1910). The first documented research of mechanics
being applied to a living system was performed by Borelli
(1608 - 1679) , who worked on determining the center-of gravity
(Leach and Dagg, 1983b). Other research on quadruped
locomotion by researchers such as Barclay (1953), Gray (1944,
1968) and.uanter (1938) established the foundation upon which

many equine studies were based.

3

One of the first documented studies of equine gait was
performed by Newcastle in 1657 (Leach and Dagg, 1983a) .
Newcastle made detailed, though crude, descriptions of various
equine gait patterns by listening to the sounds of hoof
strike. During the 1700's, Goiffon and Vincent made careful
records of equine locomotion patterns by attaching bells of
different tones to horses' legs (Leach and Dagg, 1983a). In
the 1800's, Lenoble du Teil (1877a and b, 1893), Goubaux and
Barrier (1884) all made important contributions to the study
of equine gait. They established the following understanding
of“ horse gait: successive strides were quite similar:
locomotion occurred in a cyclical manner: gait could be broken
into stance/support and swing phases: and there were both
symmetrical and asymmetrical gaits performed, such as the trot
and the canter, respectively (Leach and Dagg, 1983a).

Professor E. Marey of, France was one of the major
contributors to early equine locomotion research. In the
1870's he developed a pneumatic automatic recorder, which was
an india rubber ball filled with.horsehairu He attached it to
horses' hooves, and as they landed, changes in the balls'
shapes would be registered. Secondly, he invented an india
rubber box which fastened to the leg just above the ankle
joint. As the leg moved, pressure was exerted on the box,
which then moved a lever to record the movement on paper. His
third invention was a set of two collapsible drums to which
levers were attached to record vertical movements. These

drums were fastened to the horses' croup and withers. For

4
faster gaits, he developed a device which the rider could hold
between his teeth. Through these devices, Harey was able to
determine precise sequences of hoof contacts. His
calculations for the length of stance phase, however, were
excessive (Leach and Dagg, 1983a).

The most important early contributor to the study of
equine gait, as well as the "father of cinematography," was
Eadweard (sic) Muybridge of the United States. In his primary
work Was”) , there are nearly 800 plates of
animals, primarily horses, performing a multitude of gaits and
maneuvers. Rumors abound regarding Huybridge's colorful
entrance into the field of cinematography (Leach and Dagg,
1983a; Muybridge, 1899; Ulibarri, 1984). Supposedly, he was
hired in the mid-1800's to settle an expensive bet ($25,000)
made by Leland Stanford, financial founder of Stanford
University. Stanford wanted to prove that all of a horse's
hooves are simultaneously off the ground during a run. He
also wanted his theory proven using his favorite race horse
Occident. To perform the task, Huybridge first devised a
camera with an exposure rate of 1/500 second. Unfortunately,
the film of that era was not up to the task, and the first
photos of Occident appeared as mere silhouettes. This led
many people to question their authenticity. In 1877,
Huybridge developed a camera with an exposure rate of 1/1000
second. These photos, though, were retouched, as was typical
of that era, and again their authenticity was questioned.

Next, Huybridge set up a battery of 12 cameras alongside

5

a racetrack. Each camera was tripped when a horse ran by it.
In 1878, in California, a horse named Sallie Gardner raced by
the cameras. This set of photographs successfully showed the
horse to have four hooves simultaneously off the ground during
certain phases of the run. Huybridge was inspired and decided
to create an atlas of movement for use by artists, his work
W193. Soon after, he developed a projecting
device, his zoogyroscope, which projected his sequences of
photographs onto a screen. This was considered the forerunner
of today's cinecamera (Leach and Dagg, 1983a: Huybridge, 1899:
Ulibarri, 1984).

Today, though studies have not progressed as rapidly as
one might have expected, the technology available for studying
equine biomechanics has advanced tremendously. High-speed
cine cameras today are capable of filming up to 5,000,000
frames per second (as would be used in a ballistics study)
(Ulibarri, 1984) . Within the last decade, technology for
cinematography and videography in three dimensions has become
available, however its use in horses thus far has been limited
by cost and available facilities.

Other methods available for studying equine kinematics
include accelerometers and electrogoniometers. Accelerometers
are small, lightweight devices which attach to a body part to
measure its acceleration. They are relatively inexpensive and
both angular velocity and position values can be calculated "
(Leach, 1987) . Electrogoniometers, or elgons, are devices

positioned at the axis of rotation for a particular joint.

6
While they are relatively inexpensive and can be used for two-
dimensional, as well as three-dimensional data collection,
they have shown the following disadvantages in human studies:
they restrict normal movement, add weight, and are difficult
to secure precisely at the axis of rotation (Leach, 1987).

Force plates, force shoes, and pedobarographs are used to
analyze equine kinetics. Again, while the technology is now
available for three-dimensional analyses, its use has been
limited in equines. A typical force plate would be a
rectangular sheet of hardened aluminum with strain gauges or
piezoelectric quartz transducers placed at each corner. ‘When
a limb strikes the plate, an electric charge proportional to
the force applied is induced, amplified, filtered, and then
stored (Leach, 1987) . Force plates can measure a wide range of
magnitudes. They can measure forces as small as those
generated.by a standing animal's heartbeat, to forces greater
than a ton, which might be associated with a galloping horse
(Pratt and O'Connor, 1976) . Since sensitivity decreases
toward the edges and corners of force plates, many attempts to
achieve hoof strike in the center of the plate are often
needed (Steiss et al., 1982).

Bjérck (1958) used horseshoes with strain gauges built
into them to measure horizontal and vertical forces between
the hoof and ground. Frederick and Henderson (1970) also
developed a type of force horseshoe, but this device only
measured vertical forces. A problem with both of these shoes

was the additional weight they added to the hooves. In 1985

7
Ratzlaff et al. reported success with a lighter weight force
shoe that measured vertical forces at the walk, trot, and
canter. A ceramic piezoelectric disk was braced over the frog
by struts attached to a racing plate. A cable from the
transducer was attached to the leg and connected to a digital
integrator which converted the output to a voltage
proportional to the force. Force shoes may become preferable
to force plates since they can be used to measure successive
strides, and the problem normally encountered with subjects
trying to bypass the force plate is avoided (Ratzlaff, 1985).

A system utilized by the Scottish Farm Buildings
Investigation Unit is the pedobarograph. This system
simultaneously measures the distribution of pressure on the
limb and the three-dimensional force pattern of the limb
kinetics (Leach, 1987). Thus far, it has been used primarily
for cattle and pigs.

The following examples demonstrate how kinetic studies
might be useful. Bjérck (1958) found that when draft horses
pulled a load, the hind limbs contributed a larger horizontal
force than they did when the animals were unloaded. Dalin and
Fredricson (1972) showed that the maximum vertical force in
the forehoof of a trotter was about 8000N (Newtons) . Schryver
et al. (1978) found that peak vertical forces for the walk
were equivalent to 60% of bodyweight. Peak vertical forces at
the trot were found to be 90 - 100% of bodyweight (Quddus et
al., 1978: Schryver et al., 1978). While studying

Standardbreds and Thoroughbreds, Rooney et al . (1978) found

8

peak vertical forces at the gallop to be 175% of bodyweight.
Work by the aforementioned researchers, as well as Bartel et
al. (1978), Geary (1975), and Pratt and O'Connor (1976), has
shown that the limb (during stance phase) generates a
horizontal decelerating force and then after the peak vertical
force, generates an accelerating force. The decelerating or
restraint phase is slightly longer in the hind limbs than the
fore limbs, but in both sets lasts about 40 - 45% of the
stance phase. Also, horizontal force is minimal at toe off:
i.e. when the toe of the hoof leaves the ground.

Auer et.al. (1980) and.Gingerich et.al. (1979, 1981) used
force plates to evaluate improvement or regression in the
weightbearing ability of horses with osteoarthritis of the
knee. Rybicki et al. (1977) demonstrated that the forces
occurring in the tibia and. metacarpus while an animal
struggles to rise after being anaesthetized are greater than
those forces recorded during the trot.

A Japanese group headed by Yoko Niki has done several
studies using force plates. In 1982 they demonstrated a
difference between the walk and trot in that the walk shows
two vertical force peaks in both front and hind limbs, while
the trot shows only one peak. At the walk, they determined
peak vertical values in the front legs to be 56.2 - 68% of
bodyweight and in the hind legs to be 42.9 - 48.6% of
bodyweight. At the trot, peak vertical values registered as
105% of bodyweight in the front legs, and 92.8% of bodyweight

in the hind legs. These results lend support to the commonly

9
held theory that the fore legs provide the function of
support, and the hind legs provide the function of propulsion
(Ueda et al., 1981).

Nerkens and Schamhardt (1988) demonstrated that in
clinically sound horses the distribution of ground reaction
forces in concurrently loaded limbs was quite similar: i.e.
there was nearly complete symmetry between both the forelimbs
and the hindlimbs. Upon testing a lame horse, they found the
ground reaction forces to be significantly lowered in the lame
leg, but significantly greater in the other three limbs.
Their studies have used the Dutch warmblood horse as their
subject. They have recently developed the H(orse) INDEX to
quantify and classify horses based on ground reaction force
patterns. This standardized index combines limb and symmetry
indices. Force plate measurements from pathological horses
are compared to graphs of over 20 ”standard" Dutch Warmbloods,
which are on file. This has helped them classify locomotor
performance.

Preuschoft (1989) found that due to a horse's ability to
distribute load over all four limbs during take off and
landing for jumps, these stresses often did not exceed those
obtained during fast dressage gaits. However, he showed that
if the distal limb segments are not placed perfectly parallel
to the external force's direction, the torque may exceed the
tissue strength of bone, causing breakage.

Before equine kinetics, which is the study of forces, can

be completely understood, knowledge of the center of gravity

10

and moments of inertia of body segments must be obtained
(Sprigings and leach, 1986) . Frontal plane center of gravity
for the whole body of standing horses has been found by Benke
(1934), Kruger (1940, 1941), Rettenmaier (1950), and Bjérck
(1958) . Though the computation of changing centers of gravity
during movement had been attempted,(Hayes, 1893: Chieffi and
de Hello, 1939: Hekimian, 1970), until recently such
computations were incomplete and inaccurate.

In 1986 Sprigings and leach used Thoroughbred-type horses
to: 1) establish a standard method for disarticulating equine
cadavers for the purpose of determining centers of gravity, 2)
demonstrate a technique for locating centers of gravity in two
dimensions, and 3) present the algorithm required to use
segmental data to determine whole body center of gravity from
cine film analysis.

Using kinematic methods (those methods which evaluate
motion), researchers have discovered that horses will make
preferential use of certain limbs during exercise: i.e.
"handedness" can be observed (Bayer, 1973: Drevemo et al. ,
1980a: Drevemo et al., 1980b: and Howell, 1944). Drevemo's
group determined that racing trotters often showed a
preference for using particular limbs or a particular diagonal
pair. Using high-speed cinematography, Deuel and Lawrence
(1985b) observed bilateral asymmetry in the gallop of Quarter
Horse fillies. Given equal opportunity for choosing each
lead, these horses chose the left lead nearly twice as often

as the right, and often switched to the left lead even if they

11

started on the right lead. The researchers theorized that the
right. trailing limb ‘would. be able to ‘withstand greater
stresses. This laterality may actually play a part in
influencing athletic performances, particularly’ when one
examines data that show some horses race more successfully in
the United States than in Europe and vice versa. (Races are
run counter-clockwise in the United States and, typically,
clockwise in Europe.) Since human subjects tend to be
stronger, faster, and.more accurate on the same side of their
body as the hand they write with (Borod et al., 1984), these
findings on "horse handedness" are not unexpected.

Numerous studies have been performed researching the
relationships between speed, stride length, and stride
frequency (Dalin and Jeffcott, 1985: Drevemo et al., 1980a:
Leach et al., 1987: Rooney, 1984: and Schryver et al., 1978).
Many performance events, such as dressage, are based on a
qualitative evaluation of these relationships as they relate
to a particular judge's opinion of the ideal “way of going."

Stride length multiplied by stride frequency’ gives
velocity. Deuel and Lawrence (1985a) showed that both stride
length and stride frequency increased with increasing
velocity, at least at the gallop. Dusek et al. (1970) showed
that when speeds were greater than 12 m/sec, velocity
increases were due mainly to increased stride frequency.
Using Standardbred trotters, Drevemo et al. (1980a) showed:
that the mean stride length was 545 cm and the mean stride

duration was 455 milliseconds. The hind limbs had a longer

12

restraint period than the front limbs, resulting in slightly
shorter swing phases in the hind limbs. In a separate study,
Drevemo et al. (1980c) demonstrated that the variations in a
particular horse for stride length, stride duration, stance
time, swing time and propulsion time were very small. There
was somewhat more variation in the restraint stage. Due to
the close correlation Drevemo's group found between stride and
swing phase duration, it appeared that swing phase was the
main contributor to stride-time variation among horses
trotting. Their findings led them to believe that an analysis
of 3 to 5 strides should be adequate to gain an understanding
of a particular horse's stride. Drevemo et al. (1980a, 1980b)
and Fredricson et al. (1972) have shown very stable patterns
of repeatability when analyzing ten or more strides from
Standardbred trotters.

Schryver et al. (1978) found that.motion for the digit is
very similar at the walk and the trot. Angular velocities,
however, increased as the speed of the horse increased and the
support time decreased. The minimum value for the pastern
angle was also found to be less at the trot than at the walk:
i.e., the ankle joint sinks lower during the trot.

Rooney (1984) compiled a table showing various
researchers' results on stride frequencies, lengths, and
velocities for several gaits. Data for the walk showed
frequencies of 0.84 and 1.05 strides/sec, velocities of 1.26
and 2.26 m/sec, and stride lengths of 1.5 and 2.15 meters

(Huybridge, 1899). Huybridge found the trot to have a stride

13

frequency of 1.54 strides/sec, the velocity to be 6.34 m/sec,
and the length to be 4.12 meters. Rooney found the racing
trot to have a frequency of 2.27 strides/sec, a velocity of
13.42 m/sec, and a length of 5.9 meters. Values for the
canter/gallop ranged from a frequency of 1.33 to 2.32
strides/sec, velocities of 4.59 to 17.12 m/sec, and stride
lengths of 3.45 to 7338 meters (d'Enrédy, 1967: Pratt and
O'Connor, 1978). When Rooney made curve fittings of these
data, he found that ‘velocity to stride length. had a
correlation coefficient of 0.95. Velocity to stride frequency
had a correlation coefficient of 0.84, and stride length to
stride frequency had a correlation coefficient of 0.64.

In one of the few kinematic studies large enoughto use
multivariate statistics, Leach et al. (1987) analyzed 17
stride-timing measurements of 22 racing Thoroughbreds. The
horses were filmed at the beginning of races, while performing
right-lead transverse gallops: i.e., the diagonal pairs were
working together. Mean stride duration was found to be 0.405
sec and mean stride frequency was 2.47 strides/sec. From
their research, they predicted.that diagonal limbs should act
more synchronously and that the overlap between the lead hind
limb and nonlead forelimb would decrease as velocity
increased. It appeared that at faster velocities, these
subjects would tend to ”rabbit-hop” by using their hind limbs
more in synchrony and by dissociating the action of these
limbs from the action of the forelimbs. This type of

locomotion would appear to rely more heavily on back

14
flexibility.

Deuel and Lawrence (1988) studied neck and shoulder
motion of the gallop stride. Many differences were noted
between the body's leading and trailing sides: e.g. the
minimum and maximum heights of the scapula, which differed
from side to side. The work needed to vertically displace the
center of mass while galloping was estimated to be 98,500
J/km, which approximates 6% of the total energy expenditure
for 1 km.

Work performed by Deuel and Park ( 1989) at the 1988
Olympics provided the first quantitative documentation of
temporal patterns in Grand Prix-level dressage horses. These
researchers found positive correlations among forelimb impact
intervals, swing phase durations and the judges' scores.
Another study done on performance horses examined cutting
horses (Clayton, 1988). Clayton found that. the. highly
successful performers had faster reaction times and positioned
their body more closely, and more nearly head-on to the cow.
One study which looked into the rider's effect on horse
performance examined the effects of urging by jockeys (Deuel
and Lawrence, 1988). Their cinematographic study showed that
whipping the horse on the shoulder once per stride (typical
urging) did not increase the average velocity of 12.6 m/sec,
although it did increase stride frequency while decreasing
stride length.

One of the greatest potential applications of applied

biomechanics lies in diagnosing lamenesses. Estimates

15
indicate that over 500 million dollars are lost to lameness
annually in the U.S. Thoroughbred industry alone (Mackay-
Smith, 1977). Losses consist of lost racing days, reduced
performance, salvage costs associated with lameness, reduction
in value of lame horses, and decreased betting due to small
fields (Leach and Crawford, 1983).

In one study of lameness, May and Wyn-Jones (1987) placed
markers on each tuber coxae to help identify relative movement
of the hindlimbs at the trot. During hindleg lamenesses, the
tuber coxae on the lame side showed an increase in vertical
displacement compared to the other limb. Ratzlaff et al.
(1982) used kinematic methods to define the movements of the
carpal joints and attempted to correlate these with
lamenesses. One example of what this group found was that a
horse with a swinging leg lameness (i.e., lameness observed
while the leg is in flight) of'the right limb showedrdecreased
flexion, increased support time, and decreased angular
velocities compared to sound horses.

Using ferceplates, Gingerich and Newcomb (1979) found
that after inducing arthritis via a small intercarpal chip
fracture, horses still carried nearly 60% of their weight on
the forequarters, but dramatically shifted the weight off the
arthritic limb to the limbs on the opposite side. When
Ratzlaff et al. (1982) used electrogoniometers to evaluate
carpal lamenesses, they found the lame horses had decreased
flexions and irregular extension phases. Horses with swinging

leg lamenesses showed decreased flexion and decreased angular

16

velocities during flexion. Horses with supporting leg
lamenesses (lamenesses observed during stance phase) showed
shortened periods of maximum extension during support and
decreased angular velocities during the extension phase.

Leach (1987) stated that, "Many of the locomotion
analysis techniques generate data which may be difficult to
relate to a mental image of a moving horse. Decisions based on
these data will, therefore, have to rely on results of
statistical analysis. To refine such procedures, an adequate
data base of sound horses and horses with known lamenesses
must be available for comparison.” He feels an integration of
three-dimensional kinematic and kinetic data might ultimately
provide an effective lameness evaluation system for horses.

To date, there have been few studies performed in which
the effects of trimming and shoeing have been quantitatively
monitored. If quantitative analyses were made of the kinetic
and kinematic changes occurring after farrier modifications,
and this information was combined with any observed
pathologies or improvements, a clearer relationship could be
made to approach a more objective type of farrier science.

Rooney (1984a) devised mathematical theories to prove
that decreasing the hoof angle, i.e. , to make it steeper with
the ground causes elevation of the pastern, an increased
palmar angle of the coffin joint and increased dorsal angle of
the fetlock joint, an increased tension and strain of the deep
flexor tendon, and a decreased tension and strain of the

interosseous medius muscle with little or no change of the

17
superficial flexor tendon.

After studying the flight of the hoof via high-speed
cinematography and computer-aided analysis, researchers at the
University of Florida and the Western College of Veterinary
Medicine (Kilby, 1988) have discovered that many commonly held
theories about hoof flight do not hold true. The analyzed
hoof flights were not as smooth nor as high in amplitude as
the theoretical models. These researchers also found that
most horses' hoof angles are steeper than commonly believed -
averaging 53.5° in the front and 54.8° in the back, versus the
theoretical 45° and 50° for the front and back, respectively.
Since a wide range of angles was identified in sound horses,
it was felt that any angle which corresponded to the horse's
pastern angle was probably appropriate for that individual.
Interestingly, the common practice of changing hoof angles to
affect pastern angles was found to be an undesirable practice.
Turner's group from the University of Florida found it took
10°iof change in hoof angle to change the fetlock, or ankle,
angle 1°. This change did, however, add significant stress to
the pastern and coffin joints.

.Along these same lines, Dr. Ric Redden, who operates the
International Equine Podiatry Center in Kentucky, has also
seen more joint problems in young horses with over-corrected
limbs than with those trimmed in a balanced fashion: i.e.,
when the hooves are allowed to be of equal length on each side-
(Herbert, 1988).

When a foal is born with deviated (less than straight)

18

conformation, and is consequently correctively trimmed, Dr.
Redden expressed a concern that the foal may place undesirable
compressive loads on his unclosed joints. He says, "One
reason excessive corrective trimming has gained.popularity is
due to the optical illusion that it gives to the limb." He
has started collecting radiographs of the feet and ankles of
foals he has seen. Thus far, he has found the degree of limb
deviation has much less correlation with deformed ankles than
the correlation between this problem and highly corrected
legs. Redden does feel some correction can be beneficial if
done in moderation. He defines correction as follows: "to
take an individual with an angular limb deformity and correct
him in such a manner that the correction improves his dynamic
stability." He feels harsh corrections made on young horses
primarily for cosmetic reasons often impairs the ability of
the horse to carry his weight as an exercising adult. He
explains that while splay legged horses (i.e., the entire leg
is rotated outward) may never win a conformation class, when
considering the stress alignment of the joints, these horses
may have a minimal problem.

Unfortunately, there have been ‘very few scientific
studies done on shoeing and trimming. A great deal of open-
minded empirical evidence supports the following: leave
horses barefoot as long as possible, do minimal corrective
trimming, do not use toe grabs on shoes, and do not trim for
long toes and low heels - which is the common practice for

trimming Thoroughbred race horses (Ivers, 1985).

19

Biomechanical analyses can also be used to evaluate the
horse's competitive environment. Swedish researchers have
looked at the effects of racetrack design on limb positioning
of Standardbreds (Dalin et al. , 1973: Fredricson et al. , 1972:
Fredricson and Nilsson, 1974: and Fredricson et al., 1975 a,
b). Their work showed that the conventionally-shaped track
with its constant turn radius is insufficiently banked to
maximize performance longevity. The relatively sharp turns
appear to contribute to excessive bone stress. Cheney et al.
(1973) examined racetrack surfaces as they related to
Thoroughbred lamenesses. Not surprisingly, they found that
tracks with pliant, loose surfaces dramatically decreased the
incidence of lamenesses. I

Most of the previously mentioned works have consisted of
two-dimensional studies. Published three-dimensional
biomechanical studies are still very limited in the equine
literature. Fredricson and Drevemo (1971) used a method,
which had previously been used on aircraft, to analyze yaw,
pitch, and roll (three dimensions) of the hoof via a glass-
fiber molded shoe with coordinate markers. Unfortunately,
this system was not functional for other joints and the weight
of the shoe may have influenced movement. It did, however,
emphasize the importance of analyzing all three dimensions of
motion for certain types of studies, such as elusive
lamenesses.

Recently, Peloso et al. (unpublished data, 1990)

discovered that the human eye's slowness has contributed to

20
another myth. Using three-dimensional videography, he
discovered that horses actually raise their heads when they
land on the sound fore leg, not the lame fore leg as has been
commonly believed.

Within the last decade there has been rapid expansion in
three-dimensional motion analysis in humans. Ever since Grood
and Suntay (1983) devised a method of applying rigid body
mechanics to the knee, progress has been rapid. Shortly
thereafter, a joint coordinate system was devised for the
ankle (Soutas-Little, et al., 1987). Similar concepts, using
different joint coordinate systems for various joints should

be applicable to the horse.

MATERIALS AND METHODS

Two subjects were selected for this pilot study of three-
dimensional kinematics in horses. The subjects were two-year-
old Arabian fillies from the Michigan State University Horse
Teaching and Research Center. Both fillies were considered
"normal" (i.e. not pathological) in.both conformational build
and movement. To prepare the horses for the trial, the
fillies were acclimated to the Horse Center's treadmill for
one month prior to the experiment. The fillies were walked
and trotted on the inclined treadmill three times per week.
By the trial date, they accepted the treadmill workouts
quietly.

One of the most important aspects of this trial was to
set up an appropriate targeting scheme to detect three-

21

dimensional motion of the horse's knee (carpal) and ankle
(metacarpo-phalangeal) joints. The targeting scheme which was
developed is represented in Figure 1. Three-dimensional
analysis requires that the biological system be modelled as
though it were composed of rigid bodies. For this protocol,
the forearm and cannon were the rigid bodies for the knee
joint, and the cannon and the pastern were the rigid bodies
for the ankle joint. Three, non-colinear points were
necessary on each ”rigid body" to facilitate later three-
dimensional analysis. Two of these points had to be in line
with an anatomical axis, and all three points had to lie in an
anatomical plane. For the forearm targeting scheme, targets
one and two were aligned with the radius of the left front
leg. Targets four and five were placed just off the surface
of the metacarpus, and targets seven and eight were aligned
with the proximal and middle phalanges.

Fastening the targets to the horse to minimize target
wobble and subject discomfort was difficult. There were
several reasons why targets could not be placed directly on
the horse's skin. At the forearm, there exists a fair
quantity of muscle. This muscle moves over the bone and
distorts the true joint motion. Another problem was that as
the horses started to sweat, the targets were likely to fall
off. Regarding the pastern, there was such a small amount of
space to evaluate that it would have been difficult to place
the targets directly on the pastern and have the cameras ”see"

them without distorting the target images into "mergers.”

22

 

 

FOREARM
’Z‘r
Radius
’x‘r
A
yr
Knee Joint, Carpus
CANNON
L—— Metacarpus
A
xc
Metacarpo-phalangeal.
4? Ankle
P
PASTERN Proximal Phalanx
’5'}:

Middle Phalanx
Distal Phalanx

Figure 1. Lateral View of the left, lower leg showing
targetting scheme and coordinate systems.

23
(Mergers occur when two targets are close enough to each other
that, at certain angles, the cameras "see" two targets as one
large target.) Targets were not placed on the hoof since
there appears to be a great deal of movement between the
middle and distal phalanges: consequently, this would not have
represented an appropriate rigid body.

The forearm targeting scheme was set up in the following
manner: first, a piece of thick leather was formed to the
curvature of the horse's forearm, then a block of wood was cut
to fit the curved leather and to raise a flat, triangular
piece of leather from the horse's leg. The raised piece was
parallel to the plane of the forearm. The three targets were
positioned on this planar piece of leather with double sided
carpet tape. Elasticized bandaging wrap was used to secure
the target scheme securely to the subject's leg.

A standard splint boot (typically used on young horses'
cannons to avoid injury) was securely tightened to the cannon.
This was then wrapped with elasticized bandaging wrap. The
targets were then stuck to the wrap with the carpet tape.
First aid tape was then slit.t0>go over the targets to further
secure them. The pastern targeting scheme was similar to the
forearm model, only smaller. A velcro band was used to secure
the targeting scheme tightly to the pastern.

Targets were made with strips of retroreflective tape
wrapped around spherical bases of different sizes. (It is the
reflection from these targets that the cameras record as

data.) Forearm targets were 2 cm in diameter: cannon targets

24

were 2.5 cm in diameter: and pastern targets were 1.5 cm in
diameter. Targets were glued with epoxy to flat spheres of
leatherette material. This flat base was then easier to stick
to a targeting scheme platform than the spherical target
itself. 1

Before the horses could be filmed, the volume of space in
which the horse's leg would move had to be calibrated. The
calibration structure consisted of 16 non-coplanar control
points with known coordinates. It defined a control volume of
105 cm x 90 cm x 170 cm (see Figure 2). The four points on
each of the four strings of the calibration jigs were located
15, 45, 75, and 105 cm above the treadmill. Great care was
taken to ensure that the calibrated volume was as precise as
possible. After all distances were carefully measured, the
calibration structure was filmed to see how closely the
measured volume compared to the filmed volume. After the
first calibration setup, the residuals (determined by Least
Squares technique- Walton, 1981) were as high as 0.7. It was
discovered that the treadmill flooring floated up and down
slightly. For the second attempt at calibration, the
treadmill flooring was not touched while measuring the
calibration points. The second set of residuals registered
0.55, 0.31, 0.40, and 0.57 for cameras one through four,
respectively. Since easily tracked data had previously been
collected with residuals of 0.6 and below, these values were
deemed acceptable.

Cameras were set up in a semi arc around the left side of

25

 

 

 

105 cm

75 cm

45 cm

15 on
Y z
cw x
170 cm

Figure 2. Calibration structure, showing calibrated volume
and the sixteen coordinate points.

26

the treadmill in the MSU Equine Performance Center of the
Veterinary Clinical Center. The video cameras were set at 60
Hz, meaning that they took 60 frames of data per second.
Since each trial consisted of three seconds, 180 frames of
data were collected per trial. Camera one was approximately
12 m from the calibrated space and positioned anterio-
sagittally. Cameras two and three were located approximately
11 m from the calibrated volume and filmed sagittally. Camera
four was approximately 12 m away and filmed posterio-
sagittally (see Figure 3). If the residuals are acceptable,
and all targets can be viewed by the cameras, precisely
measured camera distances are not necessary. After the
calibration structure was removed, the horses were acclimated
to the treadmill. Since this treadmill was quieter and more
open than the treadmill the fillies had been trained on, this
was accomplished relatively easily. The horses were filmed at
a standstill (to provide offset angles for later analysis), at
the walk, and at the trot. Three trials of each gait for each
subject were filmed and sent to the video processor (Motion
Analysis VP320) . The treadmill speeds selected were 1.6 m/sec
and 3.5 m/sec for the walk and the trot, respectively.

After data collection was completed, data analysis could
begin. A program known as EV3D (Expert Vision - Motion
Analysis Corporation) was used to analyze the data. (Access
to this program was generously provided by the Human and
Veterinary Biomechanics Evaluation Laboratories). First, all

data were copied to the SUN SPARC Station 1 (Sun Workstation -

27

Calibrated Space

Treadmill

 

 

 

 

 

 

 

 

 

h Direction of Horse Movement

   

Camera 4
Camera 1

   

Camera 2 Camera 3

Figure 3. Overhead view of the calibrated Space in
relation to the treadmill, and the position of-the
cameras.

28

Sun Microsystems, Inc.) from the original data collection
disks. The calibration files from each camera were entered
and "tracked." The tracking procedure involved initializing
the computer to the target numbers seen in each camera view.
Each point was then "track edited" to ensure there were no
obvious errors in the data. Environmental variables were
entered into the program (see Table 1). Some of these values
came from the calibrated space measurements: other values were
selected based on the experiences of the MSU Human and
Veterinary Biomechanic Laboratories. After this, the horse
trials could be analyzed.

Each of the four cameras' files was first viewed to check
for merger (see Figure 4). When this happened, the camera was
interpreting two targets "merging" together; This.phenomenon
greatly reduces the accuracy of the analysis. Since mergers
were not observed in the data from cameras two and three, but
were frequently observed in cameras one and four, the latter
two camera files were "masked." In the masking program, any
observed mergers could be deleted from the data files. (This
was a plausible alternative since only two cameras needed to
"see" a target at a given time to allow three-dimensional
interpretation.) Most typically, targets eight and nine would
merge in camera views one and four, but, occasionally, other
mergers were observed.

Next the masked files were tracked using the same
procedure as for the calibration structure (see Figure 5).

Targets were identified in a frame and then the program would,

29

TABLE 1
Enzirenment

1 Segmentation Neighborhood Width (pixels) 2.00
2 Segmentation Neighborhood Height (pixels) 2.00
3 Minimum number pixels in image of single target 4.00
4 Maximum number of pixels in image of single target 25.00
5 Maximum norm of residuals (pixels) .900
6 Min. x coordinate delimiting object space (cm) -160.0
7 Max. X coordinate delimiting object space (cm) 160.0
8 Min. Y coordinate delimiting object space (cm) -90.0
9 Max. Y coordinate delimiting object space (cm) 90.0
10 Min. 2 coordinate delimiting object space (cm) -20.0
11 Max. 2 coordinate delimiting object space (cm) HHLO
12 Min. Average Speed (cm/frame) OJ)
13 Max. Instantaneous Speed (cm/frame) 200A)
14 Max. Size Change of Inelastic Linkages (%) 154)
15 Min. duration 2.0
Allowable size change in width or height of a video image 3
True frame rate - 60

Target 1 s proxl

Target 2 = distl

Target 3 - ant1

Target 4 - prox2

Target 5 = dist2

Target 6 s post2

Target 7 s prox3

Target 8 = dist3

Target 9 8 post3

Inelastic linkages:

2-3, 4-5,

5-6, 7-8, 8-9

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32

theoretically, track the data forward or backward through the
remaining 179 frames of’datam Though.these data tracked quite
cleanly (compared to other human and canine data tracked with
this program), there were still occasional problems. The
tracking had to be closely monitored to ensure accuracy. The
most commonly encountered problem was with targets seven,
eight, and nine. Due to their close proximity, the program
would sometimes switch their numbering pattern.

After tracking, the data were ”track edited" (see Figure
6). This program showed the trajectory of each of the nine
targets in the x, y, and.z directions. If there were any gaps
in the data or inexplicable deviations, small pieces of data
could be removed. However, after masking and carefully
tracking, very little track editing was required. Before
saving the track edited file, each target path was smoothed
through. a Tukey Window routine, which is part of EVBD. To
double check the track edited file, it was then run through
"exam." This program checked to make sure no extraneous data
existed and that all target path lengths were equal. A
program called "stick" was then run (see Figure 7). This
showed the paths of the forearm, cannon, and pastern triads
through the gait cycles. Note that while the horse is
travelling forward, the leg is travelling through a complete
cycle of first backward motion, then forward motion.

Another check was to run the "angle" program. This
program calculated the change in angle of a given triad.

Since the triads were fixed, the changes were hoped to be

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35

minimal. However, due to the changing of the number of pixels
observed in a target as registered in a camera view, it could
be expected the calculation would vary a few degrees by
calculating different target centroids (see Figure 8). When
a tracking mistake was made, though, the difference was
sometimes greater than 10°. (Pixels are the tiny square areas
which compose any type of television or computer screen.)

Once the files were track edited, they were run through
a joint coordinate analysis program. These programs, which
were separate from EV3D, were written specifically for the
horse's knee and the horse's ankle (MSU Biomechanics
Department). These programs were based upon a theory
developed. by Grood and Suntay (1983) to analyze three-
dimensional kinematics of the knee. The theory uses Euler
angles (yaw, pitch, and roll as used in engineering theory) to
interpret three-dimensional .motion of biological systems.
Soutas-Little et al. (1987) later used the system to develop
a joint coordinate system for the ankle. To our knowledge,
this study was the first time a joint coordinate system had
been applied to knee and ankle motion of the horse.

The joint coordinates were non-orthogonal (non-
perpendicular) systems which allowed non-sequence dependent
rotations. Local segment coordinates for the forearm were
established in the following manner (see Figures 9 and 10 for
coordinate labelling):

’2. - (F. - Fania - F2:

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36

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Xf
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A ‘
yr I:
" {b/Abduction
A
e1 A
’ Adduction
A
Zc
QC Flexion Extension

'7

J
a I .2

I

Figure 9. Joint coordinate system for motions of the knee.
Motions are of the distal segment relative to the proximal
segmentClateral view of left, front leg.)

38

Internal

,/fiotation

 

 

External
Rotation
abduction
Adduction
Flexion Extension

 

AI
e2

Figure 10. Joint coordinate system for motions of the ankle.
Motions are of the distal segment relative to the proximal
segment (lateral view of left, front leg.)

39

A A A

Local segment coordinates for the cannon:

at = (E.'-E§)/:Ek"2%:

A~ _ .. _. ._
Y; ' [/21 3‘ (F5 ‘ F5) ]/:/2\¢ X (F5 ' F5):
A A

Xe 3 ye X 9c

Local segment coordinates for the pastern:

A - — — -

zp ‘ (P7 ' I’d/:97 ' Pa:

A — — — —
y, = [’2‘9 x (P. — I’m/:9, x (P. - P,):
A _I\ A

xp - yp x 2"

Joint angles for the knee joint were designed with the
flexion/extension axis being ?, and internal/external rotation
being defined about ’21. The joint coordinates were:

a ll}; Flexion and extension

as ’2: Internal and external rotation

do) a?) ”0)

= (’e‘z x ’é‘g/Ve‘z x ’33} Abduction and adduction

The joint Euler angles were:,

1 A

Flexion/extension s -sin' (31 - 2,) Flexion is positive.

Abduction/adduction = sin.1 (1% - fig) Abduction is
positive.

Internal/external rotation =- sin" (’e‘.| - lyl) Internal
rotation is positive. These angles were of the cannon
relative to the forearm, or the distal segment relative to the
proximal segment.

Joint angles for the ankle joint were designed with the
flexion/extension axis being [Y2 and internal/external rotation

A
Z 0

being defined about 9

Pastern coordinates were rotated in

the program so as to be perpendicular to the cannon

4O
coordinates. The joint coordinates were:
1%' ==§i Flexion and extension

GQ' = 2; Internal and external rotation

’e‘,‘ a (32' x 33')/:@2' x 33'} Abduction and adduction
The joint Euler angles were:

Flexion/extension - -sin'1 (63' " £1) Flexion is
positive.

Abduction/adduction = --sin'1 (32' - ’e‘s') Abduction is

positive.

Internal/external rotation - sin.1 (31' - 2,) Internal

rotation is positive.

These equations were written into a computer program to
facilitate faster analysis of the otherwise cumbersome matrix
algebra (see Appendix 1 for an ,example of the hand
calculations for one frame of data). After the data were run
through the joint coordinate analyses programs, they were

plotted to allow visual examination of flexion/extension,

abduction/adduction, and internal/external rotation.

RESULES AND DISCUSSION
Since the joint coordinate analysis (JCA) computer
programs were newly written for the horse, a method was needed
to check the accuracy of the curves generated. The EVBD
program allowed for angle calculation between rigid bodies.
Flexion/extension graphs were thus generated by this method
(Figures 11 and 12). Figure 11 shows flexion/extension

between the forearm and the cannon, which corresponds to

41

 

 

 

 

 

 

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BS's knee while trotting. Peak areas represent maximum flexion,

Low areas represent stance phase.

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Figure 12. EV3D generated flexion/extension curve of
subject BS's ankle while trotting. Peak areas represent
maximum flexion. Low areas represent stance phase.

43

flexion/extension of the knee. Figure 12 shows
flexion/extension between the cannon and the pastern, which
corresponds to flexion/extension of the ankle. When these
graphs were compared to the flexion/extension curves generated
by the JCA programs (e.g. Figures 18 and 19), the results were
nearly identical, both in ranges of motion and shapes of
curves. Since the calculated JCA flexion/extension curves
matched the EV3D generated curves for flexion/extension, this
was a good indication that the calculated abduction/adduction
and internal/external rotation would also be correct.

Because the MSU Veterinary Clinical Center facilities do
not have a force plate at this time, identifying hoof strike
(when the hoof first comes in contact with the ground) and toe
off (when the hoof first loses contact with the ground) was
less precise than would have been ideal. Consequently, stance
phase (when the hoof is in contact with the ground) was more
estimated than exact. Stick figures of the gait cycles were
generated and compared to standing position data. These,
along with watching the stick figures during gait cycles,
helped clarify where hoof strike and toe off occurred (Figure
13). I

Upon examining the flexion/extension curves (Figures 11,
12, 16, 17, 18, 20, 23, 24, 25, and 26), stance phase can be
described as the low areas between the peaks. Since more
hyperextension occurred in the ankle than in the knee (as
could be observed visually), this coincided with the finding
that extension went lower after hoof strike in the ankle than

44

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45
in the knee.

When evaluating the standing data (Figures 14, 15, 21,
and 22) , it should be noted that subtle deviations in the
kinematic patterns occur due to the subjects shifting weight
from side to side and fidgeting. Also, in the graph legends,
several abbreviations are used: Abd+ means abduction occurs
in the positive direction, or upwards: Add- means adduction
occurs in the negative direction, or downwards: Flex+ means
flexion occurs in the positive direction: Ext- means extension
occurs in the negative direction: IntR+ means internal
rotation occurs in the positive direction: Exth means
external rotation occurs in the negative direction.

Upon examining the graphs of movement (Figures 16, 17,
18, 20, and 23-26), it is:noteworthy that stride repeatability
was very high, not only within each trial, but from trial to
trial. This can be checked by examining the curve shapes for
each gait cycle and comparing the peaks of the gait cycles.
This was particularly noticeable with the flexion/extension
graphs.. Internal and external rotation appeared to be the
least repeatable graphs, although definite patterns existed.
This apparent lowered repeatability could be artificial,
however, due to the fact that there is a comparatively small
range of motion (" 10°) taking place in this plane. The
overall repeatability that was observed helped document that
the methodology chosen for this study was effective for
analyzing flexion/extension, abduction/adduction, and
internal/external rotation of the knee and. ankle joints. Had

46

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50

there been a tremendous variation between gait cycles, it
might have indicated that there was too much wobble in the
targeting scheme or' that the calibration. area. had been
improperly selected. In addition, the treadmill proved to be
a good tool for gait analysis since more than one gait cycle
could be viewed in each trial. Typically, four gait cycles
were filmed in each.trotting trial, and three gait cycles were
filmed in each walking trial. These multiple trials also
helped in evaluating stride repeatability.

Graphs were very similar from trial to trial: therefore,
a representative graph was chosen for each condition for each
subject: i.e., one standing, knee: one standing, ankle: one
'walking, knee: one walking, ankle: one trotting, knee: and one
trotting, ankle (Figures 14-18 and 20-26). Not all curves
extend the entire three seconds that filming was conducted.
Data tended to be less predictable toward the beginning and
the end of the trials, so the ends of some trials were
clipped. (This phenomenon of lowered accuracy at either end
of the file has been observed in many human and canine trials
as well.) Standing files were edited to 1.5 seconds since
there were no gait cycles to be concerned with.

To begin with, Figure 18 will be analyzed in a step by
step manner. To review, flexion occurs when the angle between
two body segments becomes smaller, and extension occurs when
the angle between two body segments becomes larger. Abduction
occurs when a body segment, in this study the distal segment

relative to the proximal segment, is moved away from the

51

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52

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Flexion I: I
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Body
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Midline Midline Midline
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Rotation Zero Internal
Rotation Rotation

Figure 19. Descriptive drawings of the motions being
described.

53

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54

body ' s midl ine. Adduction occurs when the segment moves
toward the body's midline. Internal rotation takes place when
a joint rotates inwardly, i.e., toward the body midline, or,
for example, the left knee rotates towards the right.
External rotation occurs when a joint rotates outwardly, i.e. ,
away from the body midline, or, for example, the left knee
rotates toward the left (Figure 19).

The curve showing the greatest range of motion,
represented by the medium width line, depicts flexion and
extension. In this particular figure, the knee of subject BS
is represented. Action occurring upward, i.e. , in the
positive direction, indicates that the knee was flexing.
Action going downward, i.e., in the negative direction, means
the knee was extending. Note that while a zero point is
represented, there has been no standard definition of where
"zero" is for gait analysis. If these data were compared to
data performed under different methodology, it would be more
important to compare the shapes of the curves and the ranges
of motion than the zero points. Average standing data values
for flexion/extension have been identified on the appropriate
graphs to also use as a basis of comparison. I

Hoof strike and toe off have been marked on the first
gait cycle of each graph. Since the graphs were generated
using human plotting programs, hoof strike on the figures in
referred to in the legend as "heel strike." The areas between
hoof strike and toe off represent approximate stance phase for

all gait cycles. From toe off until the next hoof strike

 

55
represents swing phase. (Stance phase is when the hoof is in
contact with the ground: swing phase is when the leg is in
flight.)

Continuing with the analysis of Figure 18, as the subject
flexed, the knee, the lower leg ‘was abducted, which is
represented by the fine line. At maximum flexion, the knee
was as internally rotated as it would be. As the knee
extended back toward stance phase, the lower leg was adducted,
as well as being externally rotated.

The ankle graph of this same trial, Figure 20, depicts
highly superimposable curves, i.e. both knee and ankle were
reaching flexions and extensions at nearly identical times.
The first peak of flexion will be referred to as peak ”a."
The second peak of flexion will be referred to as peak "b."
This double peak flexion is an interesting phenomenon that was
at first thought to be a mistake. After all ankle graphs were
plotted and had demonstrated some form of double peak flexion,
the stick figures were reanalyzed. The modest extension
between the peaks seems to occur as the cannon moved forward
over the ankle joint before the ankle would start to flex
again.

In comparing the walk to the trot, beginning with subject
BS's knee (Figures 16 and 18) , the curve shapes are quite
similar. The primary differences were in range of motion and
length of time for completion of each gait cycle. The range
of motion for flexion/extension at the walk was approximately

60°. Range of motion for flexion/extension at the trot was

56.

approximately 75°. Ranges of motion for abduction/adduction
and internal/external rotation were also greater at the trot
that at the walk. The number of frames, or time, taking for
swing phase was more similar between the walk and trot than
was the time taking for stance phase. Stance phase at the
trot took approximately 0.20 seconds to complete. Stance
phase at the walk took approximately 0.55 seconds. Swing
phase took approximately 0.45 seconds at the trot and
approximately 0.50 seconds at the walk.

In comparing the walk to the trot with subject EC's knee
(Figures 23 and 25) , the curve shapes were again quite
similar. The range of motion for flexion/extension at the
walk was approximately 63°. The range of motion for
flexion/extension at the trot was approximately 76°. Ranges
of motion for abduction/adduction and internal/external
rotation did not differ as much between the walk and trot as
they did for subject BS. Timing lengths for stance phase and
swing phase were quite similar to those of subject BS, again
differing primarily in stance phase length.

Regarding subject BS's ankle graphs (Figures 17 and 20),
there were more differences in shape than had been observed in
the knee. The first flexion peak will be referred to as peak
”a," and the second flexion peak will be referred to as peak
"b.” At the walk, peak ”a" was a larger percentage of "b"
than what occurred at the trot. Also at the walk, during
stance phase, there was a subtle flexion at approximately

. midstance. This appears not to have happened at the trot.

 

57

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63
Since the ankle was extended even while standing, most of the
flexion/extension curve occurred on a negative scale. The
ankle sinks considerably during stance phase for shock
absorption; consequently, there was a greater continued drop
between hoof strike and toe off than what was observed in the
knee.

Differences in stance phase and swing phase timings were
nearly identical to those observed in the knee. Ranges of
motion for the ankle at the walk were approximately 55°
flexion/extension and approximately 70° flexion/extension at
the trot. Less abduction/adduction took place in subject BS's
ankle than occurred in her knee. Unlike the knee, maximum
internal rotation in the ankle occurred at approximately
midstance during the trot.

The most striking difference when looking at subject EC's
ankle graphs (Figures 24 and _26) is that at the walk, peak ”a"
is larger than peak "b." This differs from this same
subject's trotting files, as well as subject BS's walk and
trot. Again, the walk graphs were checked and rechecked to be
sure this was not an error in analysis. Each check showed the
same position of the peaks. With only two subjects, it is
impossible to say which subject more closely represents
"normal. " Since neither subject demonstrated pathological
movement, perhaps both are "normal, " though one may be more
nearly "ideal" than the other.

Flexion/extension ranges of motion for subject EC's ankle

were approximately 52° at the walk and 65° at the trot. There

64
was less difference in scale between peaks "a" and "b" for
subject EC's trot than had been observed for subject BS.

Ankle graphs for each condition and each subject were
easily identifiable without looking at labels. Knee graphs
were somewhat less distinct in their differences between the
two subjects, though walk and trot were easily differentiated.

Cross plots, or angle-angle diagrams, of knee against
ankle flexion/extension were also plotted (Figures 27-30) .
The graphs depict approximately three gait cycles for the walk
and approximately four gait cycles for the trot. Motion on
the plots proceeds in a counter-clockwise direction, and the
condensed area in the lower left of each plot represents
stance phases. Plots both stretched and narrowed when going
from the walk to the trot.

Cross plots probably have the most potential usefulness
when analyzing pathologies or documenting interactions. For
example, the range of motion of horses with osteoarthritis
could be compared before and after administering an anti-
inflammatory drug. Also, it has been noted in human studies
(Soutas-Little, 1991) that often a pathology in one part of
the limb will cause compensatory actions in another part of
the limb or in the opposite limb. These interactions are more
quickly analyzed using a cross plot than by analyzing the

entire set of data.

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0.00 5.00 10.07 10.00 21.33 20.07 32.00 07.33 42.07 40.00 00.03 50.07 04.00 00.33 10.01 00.00

(Degrees)
KNEE

Cross plot of knee against ankle flexion/o
The direction of motion is counter-clockwise.

This plot is for Subject BS while walking.

66

    

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extension. The direction of motion is counter-clockwise.
This plot is for Subject BS while trotting.

67

 

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e w e
-usm- MaXimum Knee .lex1q’

  

'10.20 1 -

ANKLE
(Degrees)

423.001-

-ae4o J .

V

-35.00<

«mm» .
Stance Phase

   

40.201

V

-51eao" {p

-570‘0" 4p

 

 

 

'53.00 3 i C 2 C ; f C C C 2 ‘f ‘f f
0.00 5.33 10.67 16.00 21.33 25.67 9.00 37.33 42.07 40.00 53.33 50.67 ELM “.33 74.07 00.00

(Degrees)
KNEE

Figure 29. Cross plot of knee against ankle flexion/
extension. The direction of motion is counter-clockwise.
This plot is for Subject EC while walking.

68

 

no A A A A A A A A A A A A A A
' I V v W v v

.150‘0 ‘ "

48.001

04.20”

 

'1.40‘

V

    

-Lmu Maximum Knee Flexio

’12060 ' "

‘16020 ‘ '

ANKLE
(Degrees)

-20.00‘»
-20.40+-
-00.00..
-40.00<L
40.20”-
'5‘-°°‘r

Stance Phase
-s7.40‘»

 

 

-amo 3 : : : e f r : : : : : .4. c
0.00 5.00 10.07 10.00 21.33 20.07 02.00 07.33 42.07 40.00 00.03 00.07 04.00 00.03 74.07 00.00

(Degrees)
KNEE

 

Figure 30. Cross plot of knee against ankle flexion/
extension. The direction of motion is counter-clockwise.
This plot is for Subject EC while trotting.

69

CONCLUSION

This study describes appropriate methodology for three-
dimensional kinematic analysis of the horse's knee and ankle
joints. The targeting schemes, camera set-up, calibration
area, and joint coordinate analysis programs all contributed
to producing reproducible data.

One suggestion for future studies is to have the
additional benefit of a force plate or, perhaps, force shoes,
to facilitate simultaneous collection of kinetic data. Force
data would also enable more accurate identification of hoof
strike and toe off. Kinetic data may contribute greatly to
more clearly identifying lamenesses, since uneven
weightbearing would be detected.

The follow-up step to this study would be to analyze a
large enough sample of "normal" (i.e., horses without a
noticeable pathology) horses so that baseline data could be
accumulated. Since there are most probably breed, age, and
training differences among horses, these factors would need to
be considered and accounted for. Next, studies of lameness
and corrective farrier work (trimming and shoeing) could
commence. Studies in these areas would ideally look at all
four limbs, at least on some of the subjects, to check for
compensatory mechanisms that might be taking place. These
studies would hold tremendous potential for the horse
industry.

Human biomechanics studies are becoming an acceptable

70
clinical tool, rather than strictly a research tool. Perhaps
in the future, gait analysis will be a routine clinical tool

for the evaluation of horses.

APPENDIX

APPENDIX 1

Mathematics involved in calculating frame 1 for the knee of
subject BS (see also Figures 1, 9, and 10):

F1, F2, F3, C“ C5, C0! P7, P0: and P9 will all be represented by
the actual positional data for each with respect to the
calibrated area. Each coordinate is defined by a vector value
in the x, y, and z directions. The first three values
represent targets 1, 2, and 3 of the forearm; the second three
values represent targets 4, 5, and 6 of the cannon; the final
three values represent targets 7, 8, and 9 of the pastern.

’2‘, ' (3‘1 ' i'2) / :FI ’ F2:

A
= -1o.172’1‘, - 1.229’1‘y + 52.2101, (x, y, and z coordinates
for target 1 on the forearm)

- (-15.934’i‘, - .510?y + 42.925?) (x,y, and z coordinates

for arget 2 on the forearm)

+ (5.7022 + .7192 + 9.2912)"2 (This 10 the manner in which
vector absolute values are calculated; after the difference
between the x, y, and z values of F, and P2 are calculated,
these differences are then squared. The values are then added
and the square root of the total is taken.)

A
- .520’1‘, - .0001y + .048’1‘, 00*

3h 3 f9;lt(ih “.Efl] /':€L x (Fj"ifl):

"x" symbolizes a cross product and is computed in the

following manner (using A - F as variables that show how to

calculate cross products regardless of the values):
I

 

 

A
’1‘, 1, ’1‘,

A B C
- (BF-CE) 1,- (AF-DC) 1Y+ (AE-BD) 1,

E F

A A A -

-22.010 1, -.761 i, + 46.953 i, (position values for F3)
- - A, -,§1Q A1 + 52,225 A1,) (position values for F2)

A A
-0.074 1, - .251 1, + 4.020 ’1‘,

71

->

.526

 

-6.074

/.\
1Y
-.000

-.251

‘fi
12

.848

4.028

72

.«

(see zf from above)
A A A
-«=&Q2i—iw4141LZZQ—iv¥:—L§11—i2

 

(«0542 -7.2702 -.5332 )"2

A A
= -.007 1, - .997 ’1‘, - .073 1, mt

A A A
xf-yfxzf

’1‘.

-.007

 

l.\
17

-.997

-.073

(’y‘f values from above)

A
- -.050 ’1‘, -.032 1, + .524 ’1‘, 00*

 

(’z‘, values from above)

+ 30.469 3; (position galues for

Ck)

A A A
.(.34 952 1‘ + 5,453 1 + 2Q,1§1 1,) (position y_alues for

A A
4.220 1, + .472 1, + 10.310

A A
=- .379 i, + .042 i, + .925

A
Z

?c-[?cx(ES-E6)]/:cx

-34.042

1

 

’1‘.

.379

+ 4.458

A

1,

.042

C5)
"‘, / (4.2202 + .4722 + 10.3102)"2

1
A
1, 00*

(60"Ei):

4» 20.151 (position values for is)
-(.. 23,235 + 5,321 + 1§,§§§) (position values for C0)

A A A
-10.3001, - .0031, + 3.4051,

’1‘.

. 925 (values for ’z‘,)

——&2AAIW;LLQL§§11rJL‘1Q§i1

: «(.9442 + 10.0542 + .1002)"2

 

I '73

I ‘ -

-10.306 -.863 3.485 ' (difference between C5__and
C0)

= .007’1‘, - .990’1‘, + .010’1‘, am

 

 

.9) 09> ~10) 0 I0)

 

 

A. xx
xc - y, x zc
/. xx 40
i, i, 1,
.087 -.996 .010 (/y\c values from above)
xx x« xx
' .0921j.x -0076iy +038112 ***
.379 .042 .925 I (€2values.from above)
1, 32, and ’e‘, represent the Euler angles of motion (see Figure
).
xx
as 1;,
xx
8 zc
xx xx
=(e\2xe3)/ :ezxe3:
1A /\ IN
1, 1, 1,
xx
-.007 -.997 -.073 (values for 22 - yf)
Mxmm,
- ' (.9252 -+.0222 +0792)"2
.379 .042 .925 (values for a =- ’z‘,)
= -.925’1‘, -.021’1‘, +.300’1‘, 1m
internal/external rotation - sin.1 (’e‘1 . ’y‘c) (For dot
products, represented by "II", only the values are

important, not the direction)

(values for 8,) (values for y,)

-.080 (this is the first values multiplied together)
+.021 (this is the second values multiplied together)
+.004 (this is the third values multiplied together)

 

-.055

=- sin°1 -. 055 o
= -3.10 ***

flexion/extension = -sin'

(-.925 -.022 +.379). (.520 -.000 +.040)
(values for 6‘.) (values for 9,)

-.487 +.001 +.321 3 -.165
= -sin'1 -.165
a 9.49? 100*

abduction/adduction = sin.1 (’e‘z . ’e‘3)

(-.007 -.997 ".073) 0 (.379 +.042 +.925)
(values for ’e‘z) (values for 6‘3)

-.003 —.042 -.000 = -.113
- s1n'1 -.113
= -0.400° ***

Mathematics involved in calculating frame 1 of the ankle for
subject BS:

’z‘, - .3793}, +.042’f, +.925’i‘, (see knee calculations)
A
’3}, - .0871, -.996’i‘, «010?, (see knee calculations)

A .
Q, :- -.921i‘, -.0761, +.381’i‘, (see knee calculations)

’2, - (57 ’50) / :37 ‘30: (x, y, and z coordinates from targets
7 and 8 on the pastern)

+ + - 77

A A
4.1791, +1.3011, +4.442’1‘,

A A
(4.1792 +1.3012 +4.4422)"2 = .0701, +.2091, +.712’1‘, 0*
A - - A - -
y, - (2‘, x (P. -P.)1/:z, x (P. - 9.):
-36.826 -1.915 +6.776 (position values for Ea)

+32 52; 4.1.299 -;,922 (position values for ,)

 

75

 

 

-4.233’1‘, -.715’1‘, +3.004’1‘,
I
A A A
i, 1, i,
.670 .209 .712 (values for ’21)
A A A
Wx—LM + Z
- (1. 2792 +5. 4012 +. 4005‘”
-4.233 -.750 3.004
- .277’1‘, -.971’1‘, +.072’1‘, 0*
A A A
x, ' Y0 x z,
A A /,\
i, i, 1,
.227 .971 .072 (values for 9,)
- (-.091 -.015)’1‘, -A(.102 -.040)’1‘, +
(.047 + .051)1,
.670 .209 .712 (values for ’z‘,)
**

 

= -7062,

-. 114’1‘, +. 090’1‘,

ls“ , 92' , ’e‘,‘ represent the Euler angles of motion (see Figure

 

 

10) O
A . A A
e, -’9,= .0071, -,.9901 +. 0101,
63' - ’z‘, - .0701, +. 209’1‘, +. 712’1‘,
’éa' - (5‘2 x 3‘s) / I’éz' 393':
A A A
1, 1, 1,
.087 -.996 .010 (values for ’e‘,)
A A A
- 2111‘ -,Q§§1I +I§§§iz
=- (.711’ +.0552 00052)"2
.070 .209 .712 (values for ’83)
- -.719’1‘, «0501‘, +.093’1‘, *0
flexion/extension a -sin'1 (81' 0 2,)

(-.719 -.050 +.093) . (.379 +.002 +.925)

76

‘ .366

= —sin'
= -21.47° **

abduction/adduction = sin'1 (’e‘.,,' . ’e‘,‘)

(.087 -.996 +.010). (.670 +.209 +.712)
.058 -.200 +.007
= sin” -.143

= -8.22° **

internal/external rotation = sin'1 (6". 9‘9)
(-.719 -.056 -.693). (.227 -.971 +.072)
-.163 +.054 +.050
= sin4 -.059

= -3.388° **

LIST 01" REFERENCES

77

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