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The effects of a compressible plastic shoe - The Seattle shoe®- on the kinematics of the strides of galloping thoroughbred horses
:.~i~~i~i~~ ! ~
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Refereed
THE EFFECTSOF A COMPRESSIBLEPLASTICSHOE - THE SEATTLESHOE®ON THE KINEMATICSOF THE STRIDESOF GALLOPING THOROUGHBRED HORSES Patrick D. Wilson, MS, DVM;a Marc H. Ratzlaff, DVM, PhD;1 Barrie D. Grant, DVM, MS; 2 Martha L. Hyde, PhD;1 and Olin K. Balch, DVM, MS1
SUMMARY
This study was undertaken to determine if the kinematic parameters of galloping horses were altered when these horses were shod with Seattle Shoes®. Analyses of films of six Thoroughbred horses galloping through a track straightaway, with and without Seattle Shoes®, were used to determine velocity, stride length, stride time, swing time and support time ofthelimbs, the percentages of the stride time spent in the swing and support phases, and the arcs of flight of the carpi and fetlocks of the forelimbs and the coronets of all four limbs. Descriptive statistics were calculated for each of these variables. Comparisons were made between those measured from horses shod with and without the Seattle Shoe ®,usingboththe paired-t test and analysis of covariance, which eliminated the influence of differing velocities. No significant differences occurred in the stride lengths or timing parameters when these Authors' address: 1Departmentof Veterinary and Comparative Anatomy, Pharmacology and Physiology, Department of Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman,WA 99164; 2SanLuis Rey Equine Clinic, 4211 Holly Lane, Bonsall, CA 92003; 3Departmentof Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, "IX 77843. Address correspondenceto Dr. Ratzlaff. Acknowledgments: This study was supported by Kinesis, Inc., Salem Oregon. the assistance provided by Jane Koepcke, Lisa Wood and Marry Bennett is greatly appreciated.
374
horses were shod with Seattle Shoes®. The Seattle Shoe ®had it's most significant effect on the arcs of flight of the limbs. The compression of the Seattle Shoe ®appears to store a portion of the potential energy normally stored in the suspensory apparatus and results in a decreased extension of the fetlock. This energy is then released, causing significant increases in the heights of the forelimb during retraction and protraction. Although kinematic adjustments are required by horses to maintain the level of performance, the Seattle Shoe®appears to have no detrimental effects on the performance of galloping horses and it may decrease strain on the suspensory apparatus.
INTRODUCTION
There has been a long-standing interest in providing athletic horses with the proper footwear to both increase performance and to prevent or treat lameness. Hoof pads inserted between the shoe and the hoof have been used for sole p~otection, shock absorption, and for accentuating the action of gaited horses. 1,8 The greatest disadvantage of the use of hoof pads is the tendency for the shoe to move in response to the compression of the pad which loosens the nails and results in greater damage to the hoof wall. "Nailless" shoes and "Pour-On" pads have gained popularity for the prevention of problems arising from excessive hoof wear and as a treatment for lameness,a,s Reports indicate that of all the footwear
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:iii•~iii~i
Figure 1.
The Seattle Shoe® prototype used in this study.
A. Ground surface with metal wear rim removed. 1 = shelf for nail holes, 2 = thread hole for attachment of wear rim.
Figure l B . Ground surface with aluminum wear rim.
designed for use in horses, only two have been tested scientifically to determine the effects on the performance of the horse. These are the Budkirk Nature Plate®and the Seattle Shoe*. The Budldrk Nature Plate* was designed to be a "natural" extension of the hoof with the intention of maintaining the normal angles and configuration of a physiologically normal hoof.14 This shoe was reported to be a valuable adjunct in the treatment of lamenesses. TMThe disadvantage of the Budkirk Nature Plate* is the careful foot preparation and fitting required for optimum results. The Seattle Shoe* has been shown to be a valuable adjunct in the treatment of museuloskeletal lamenesses. 3,6 This shoe was designed with a compressible, hourglassshaped spring to absorb and store the energy of the impact force and return it to the limb. The effects of the Seattle Shoe* on the concussive forces experienced by the limbs, and the effects of the spring design on locomotion have not been reported. The desired effects of the Seattle Shoe* would be to absorb the impact force and decrease the strain on the suspensory apparatus of the fetlock, similar to a track with a loose cushion and soft, pliant base.l°.12.16Instead of a reduced recoil or "rebound energy" of the limb as Cheney et al.4 observed on such a surface, the impact force would be stored in the shoe and released, creating greater recoil of the limb and greater efficiency of the stride. This study was undertaken to determine if any alterations in the timing components or arcs of flight of the limbs of galloping horses were present when these horses were shod with Seattle Shoes*, when compared to being shod with standard aluminum racing plates.
=Delrin,DupontCompany,Wilmington, Delaware.
Volume 12, Number 6, 1992
Figure 1 C . Side view without the metal wear rim. 1 = toe clip on foot surface.
METHODS AND MATERIALS
The Seattle Shoes* used in .this study were machined from an acetal resin a and consisted of two plates connected by an hourglass-shaped spring (Fig. 1). The foot plate, the portion that lies adjacent to the hoof, had lateral and medial shelves for the placement of nail-holes. Four screw holes in the ground plate allowed for the attachment of wear rims, which were milled from aluminum. The shoes measured 3.8 centimeters in thickness when nonweight bearing, 2.8 centimeters when fully compressed, and weighed 310 to 325 grams. The aluminum racing plates used as the control weighed 76 to 85 grams. Six clinically sound Thoroughbred horses, undergoing a daily training regimen of one mile at a trot followed by one mile at a gallop, were used in this study (Table 1). Side view movies were taken of each horse with a high speed 16mm camera b positioned perpendicular to and 30 meters from the running line. Each horse was photographed with black and white filmc at a speed of 300 frames per second as it galloped through the straightaway. Each horse was shod with either standard aluminum racing plates or with Seattle Shoes* and therefore, served as its own control. After being shod, at least three days of regular work-outs were allowed for the horses to become accustomed to the shoes before filming. The skin over specific sites of each limb were marked with one-half inch dots of white cosmetic paste, d These sites were the lateral and medial collateral ligaments of the carpus at the level of the middle carpal joint, the center of rotation of the metacarpophalangeal (fetlock)joints, and the lateral and medial sides of the coronet on all four limbs. The inside rail and posts of the track were removed to allow unobstructed visualization of the horses. White lime 375
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•
•
%
%~.
#
Table 1, Signalment of horses. Horse
Age =
Breed n
Sex =
Weight a
1 2 3 4 5 6
4 7 7 11 3 3
TB TB TB TB TB TB
G G G F F F
1150 1125
1050 1005
850 925
=years bTB=Thoroughbred CG=geldodmale; F=female
dpounds
was used to mark a running line on the track four meters from the inside rail on the straightaway. Five reference markers were filmed: Two reference stakes were placed on the running line 5.0 meters apart, two reference stakes were placed directly behind these stakes on the outside rail and a post with 0.5 meter gradations was centered between the two stakes on the running line. After filming these reference markers, the two stakes on the running line were removed and the post was centered between the two stakes on the outside rail. The stakes and post were then left in position on the outside rail to provide reference distances during filming of the horses. On the days of filming, the horses were trotted one mile followed by two 3/16th mile gallops which transversed the straightaway during the final 1/8th mile. The horses were filmed at this time. The horses were walked and trotted for 10 minutes between each trial. The f'dms of two consecutive strides were analyzed ~ frame by frame to determine the stride length, timing parameters, velocity and the arcs of flight of the carpi, fetlocks and coronets. The timing parameters included swing time, support time, stride time, and individual limb overlap times. The heights of the carpi, fetlocks and coronets at hoof contact, maximum support, hoof lift, and during retraction and protraction were measured from the arcs of flight. Retraction is defined as the portion of the swing phase where the limb is lifted, or retracted from the ground, and protraction is the portion of the phase where the limb is extended forward and returns to the ground. The swing phase of the limbs were further characterized by calculating the differences between the maximum heights of the carpi, fetlocks and coronets at retraction and protraction with these heights during maximum support and the minimum heights during the swing phase. Additionally, the differencesbetween the minimum heights of bModelIPL, PhotoSonicsCorporation,Burbank, California. ¢Tri-X7278, EastmanKodakCompany,Rochester,New York. dCIownWhite, Ben Nye Makeup, Inc,, Los Angeles, California.
376
the carpi, fetlocks and coronets during the swing phase and these heights during maximum support were determined. Subtracting the heights of the various points on the limb during the swing phase with their heights at maximum limb support was used to compensate for the difference in the height of the Seattle Shoe*. Stride lengths for each limb were also measured directly from the track by averaging the distance between contact of each hoof from four successive strides. Descriptive statistics (mean, standard error of the mean, and coefficient of variation) were calculated for each variable. A paired-t test was used to compare the values of each variable measured when the horses were shod with the Seattle Shoe ® versus the aluminum racing plates. The General Linear Procedure of the SAS Analysis of Covarience was used to eliminate the influence of the differing velocities on each of the stride parameters and to obtain the adjusted means and the standard error of the mean. In this procedure, the variation in velocities between horses was eliminated and the data was adjusted using velocity as a covariant. During the support phase of each limb, the minimum height of the coronet was subtracted from the minimum height of the fetlock. Because of the relatively large standard deviation of the resulting differences, the chi-square test was implemented, categorizing the values ofx >O as 1, O >x>-0.01 as 2, and x <-0.01 as 3. A significance level of p<0.05 (a<0.05 for chi-square) was used for all statistical procedures. Emphasis was placed on the timing parameters and on those variables related to the arcs of flight of the limbs that were significantly different when the horses were shod with the Seattle Shoes® versus the aluminum racing plates, after making adjustments for differing velocities. The absolute arcs of flight are those measurements made from the ground to the marked point on the limb. The relative arcs of flight are the same measurements relative to the height of these points at the middle of the support period of the limb (Fig. 2).
RESULTS The velocity, timing parameters (stride time, average litnb support and swing times, the percent of the stride times spent in the support and swing phases, and the ratios of the support time to the swing time) and the stride lengths were not significantly altered by the Seattle Shoe* (Table 2). The absolute arcs of flight of the carpi were higher in these horses when shod with the Seattle Shoe® (Table 3). The carpi of both the lead and nonlead limbs were significantly higher during maximum limb support and protraction; the
JOURNAL OF EQUINE VETERINARY SCIENCE
.... ~ ! ; . . - %
A 1.2 1.0
Carpus
0.8 0.6
o.,I o.~r . DISTANCE
l
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.
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.
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.......... ""
.
¢/) 1.o Fetlock nl O.4
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q
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...................................................................
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.
0.4 0.2 0
....................................................................
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o
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1
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2
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3
'
4
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5
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METERS
Figure 3. Arcs of flight of the carpus, DISTANCE
Figure 2.
fetlock and coronet of horse 3 galloping at similar velocities when shod with Seattle Shoes ® and with aluminum racing plates.
Methods for measurements from the arcs of flight
point on the limb (carpus) ~ = hoof contact, 1' = hoof lift. ~ •a Measurement of actual values. 1 = minimum height during full support, 2 = height at hoof lift, 3 = maximum height of retraction, 4 = minimum height during swing phase, 5 =
maximum height of protraction and 6 = height at hoof contact. B . Measurement of the relative heights, a = maximum height of retraction minus minimum height during full support, b = maximum height of retraction minus minimum height during swing phase, c = maximum height of protraction minus minimum height during full support, d = maximum height of protraction minus minimum height during swing phase, • = minimum height during swing phase minus minimum height during full support.
minimum height during the swing phase was significantly higher in the lead carpus; and the height of the lead carpus was significantlyhigher at the time of hoof contact. The differences in the arcs of flight of the carpus, fetlock and coronet of the lead forelimb of one of the horses when shod with aluminum racing plates and when shod with Seattle Shoes®are illustrated in Figure 3. The relative arcs of flight of the carpi were lower during retraction of the limb when shod with the Seattle Shoe®, but higher throughout the rest of the swing phase (Table 7). The elevation of the lead carpus was significantly lower during retraction and the descent of that carpus to the minimum swing phase height was also less. The elevation of both carpi from the minimum swing height to the maximum height of protraction were significantly higher with the Seattle Shoe®. The absolute heights of the fetlocks were higher throughout the arcs of flight for the horses st.od with the Seattle Shoe ® (Table 3). The fetlocks of both the lead and nonlead limbs
Volume 12, Number 6, 1992
were significantly higher at the maximum heights of retraction, the minimum heights during the swing phase, and the maximum heights at protraction. The height of the lead fetlock was significantly higher during total limb support. The relative heights of both the lead and nonlead fetlocks of the six horses shod with Seattle Shoes ®were significantly higher throughout the swing phase of the limb with a significantly smaller descent from the height of retraction to the minimum height of the swing phase (Table 4). However, this descent of the lead fetlock was not significant after adjusting for velocity. The absolute heights of the coronets of the front limbs were higher throughout the flight of the limbs when these horses were shod with the Seattle Shoe®(Table 3). The heights of the coronets of the lead front limb were significantlygreater at the times of hoof contact, hoof and limb support. The coronets of both the lead and nonlead front limbs were significantly higher at the maximum heights of retraction, the minimum heights of the swing phase and the maximum heights of protraction. The relative heights of the coronets of the lead and nonlead front limbs of the horses shod with Seattle Shoes® were significantly greater at the maximum height of retraction, the minimum height of the swing phase and at the maximum height of protraction (Table 3), with a significantly smaller rise of the lead front coronet from the minimum height of the swing phase to the maximum height of protraction (Table 4). When the horses were shod with aluminum racing plates, the fetlocks of the nonlead limb dropped twice as far below the
377
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~ ~ ..............
!".~
...............
Table 2 . The means, standard error of the means and significance of the velocities, stride lengths and stride timing parameters before and after adjustments for velocity. Parameter Velocity
Shoe" alum
(m/sec)
S-S
:iii iiii !i!:i
Mean 15.2
Range 11.6-16.8
SEM .488
CV 11.1
15.4
11.9-16.9
.370
8.33
i ii !!i
iiiii:i
!:! : ? ?i
iiiil ! i::
i i iiii
.414
.370-.497
.009
7.31
(see)
S-S
.412
.376-.475
.008
6.72
ii::i:~ill~ i ::!
~~ 5;~;i 28
.306 .306
.268-.360 .271 -.347
Swing time
alum S-S
(sec)
itim~i:11: : i[:
% Support time
%s~g time !!
Si
i
i i i i::iS~S
i:ii:;i:;::iL345:::
::::
::i:
alum S-S
26.0 25.6
H u m :. sis
!
i:::
i!:: ii~OO8
i + i
24.4-27.8 23.3-28.3
: ::74~0 ! i~4i4
NS
.003 .004
::i72~4.~75i6; 7!:~7-76;7 i
!i003: !i
i i!::i :i
6.85 7.05
;1!
i::
4.22 5.80 i :I~43: i.95!: !:
.412
.005
NS
.414
ii:. i 8~46!iii .006 .006
Slg c
NS
...........
alum
!:i
Adjusted Sem
Mean
!~ii! i:i : i i :h:::::::::::::
Stride time
(s~)! !:;i
Slg c
NS
~;
iii:i !ii: i
;
iili .305 .308
::::.::1:. ! NS
.005 .
::ii NS
:.:::::.~346: i i:: : :.i::ii : : : : i l t 26.0 25.7
NS::
.003
NS
! i:. ! i003 :
N8: :::::
.002
NS
Overlap Tlmes b (sec)
NR-LR
::: NR-NF
alum S-S
.044 .044
:. :ii:::ii!:S ! S
:~0~
alum S-S
.005 .002
0-.034 0-.018
.004 .002
~022
::i008:~.04.0
:i :: : i022:i::.:: : .
.002 .002
0-.016 0-.018
.002 .002
i LR-LF
alum S-S aalum = aluminum racing plate S-S = Seattle Shoe ® bNR = nonlead rear limb LR = lead rear limb NF = nonlead front limb LF = lead front limb "NS = not significant, p>0.05
i
.037-.053 .034-.056 :
.001 .002
NS
0I i~ii i:
.044 .044 ::
coronets on the average than they did when shod with Seattle Shoes® and the fetlocks of the lead limb dropped more than three times as far on the average than they did with the Seattle Shoe® (Table 5). The relatively large standard deviations made the paired t-test invalid for statistical analysis of the significance of these differences. The chi-squared analysis, however, showed the distribution of these values to be significantly different (Table 6). When the horses were shod with Seattle Shoes®, the maximum height of retraction and the minimum height during
378
10.1 14.2
235 255
NS
::: 239 347
NS
! !::ii: ii04:i:. :: :.!:: : : i i: .005 .003 : ii::::;ii:::: : :~023 i .002 .002
,001 .003 i:023 :~:~:~::~i .001 .002
NS
~i:~ NS
the swing phase of the lead rear coronet were significantly higher (Table 3). After adjusting for velocity, the relative height of retraction of the lead rear coronet was no longer significantly different between the two shoes (Table 4). No significant differences were seen in the heights of the coronet of the nonlead rear limb when the horses were shod with Seattle Shoes®versus aluminum racing plates (Tables 3 and 4).
JOURNAL OF EQUINE VETERINARY SCIENCE
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Table 3 . T h e m e a n s a n d standard error of the m e a n s of the heights (in meters) of the arcs of flight v a r i a b l e s after adjustments for velocity.
Hoof contact
Hoof lift
NL Carpus Mean SEM .483 O.15 .520
Shoe alum S-S
M~i~Om
alum S-S ~u~ :
.493 .507 505
Minimum swing
alum S-S
.406 .429
p~i~a~ion:, i
~.:~S~Si.
Hoof contact
Shoe alum S-S
:
:s;s
:
L Carpus Mean SEM *.462 .012 .515
.011 : 10i3 .013
~::.:.i!:!~
~:
: :i:;09! :!
.011
*.420 ,470
.009
~
SiS
Minimum alum swing S: S M~mOm i alum i : ; p~ra~i~ ::~S~S *Significantly different p<0.05.
*.349 .464 '51i
::
:i01~ i
.245 .273 i*:5~ ii
.013
*.471 ,593
,144
,013
:::::.: :.728:ii i:
ili
~i2~ ::~:ii : :
NL R Coronet Mean SEM .132 .006 ,131
i: :::io97ii:.
alum .118 .005 *.115 S-S .132 .131 Maximum .......................alum ............................. 5 ~ .................0 t 5 ................. ~58
L Fetlock Mean SEM .209 .013 .235
.011
*,441 ,527
LF Coronet Mean SEM *.122 .006 ,143
Hoof lift
re!!~ ~
.254 .271 ~15~7!
!i11:
NL F Coronet Mean SEM .124 .007 ,134
~
.502 .526 :: ! ~510!
NL Fetlock Mean SEM .200 .011 .232
L R Coronet Mean SEM .146 .007 ,136
i ~ 8 i i iili:i
ii:i
:.:i:ii
.005
.134 .007 .136 .006 .123 .133 , !9 ........ .......... : 5!6 .........., ~ 2 ................... .............5 ~ : ::: : ~ 0 2 6
.016 *.384 .026 .378 .015 *.348 .018 . . . . . . . . . . . . . . . . . . . '.552 .....................................:366 ........................................ ~4~ . . . . . . . . 019:i. *,538 0 2 8 :~81 ~017: 017: ::: i ~6~: iii ~:: ~: ~.:: :::.~7:1 i:~.: ~i i i:i:: iS:}! ::i:
Table 4, The m e a n s a n d standard error of the m e a n s of the relative heights (in meters) m e a s u r e d from the arcs of flight (see Figure 2) after a d j u s t m e n t s for velocity.
NL Carpus L Carpus NL Fetlock Shoe Mean SEM Mean SEM Mean SEM Max retract alum .I 19 .012 *.135 .005 *446 0.10 - m n supp S-S .097 .I 17 .490 Max retract:: i:i:ii ii :alum: .............:.:.: ,091:.: : :..:~,008 :.::: : : : : : , . :,090: :: :: ~007 ::. :.: ....::: ::: . : :,0 : ::
L Fetlock Mean SEM *.475 .013 .542 ,:::,.:.: ::............... 068.: ............O!0 ....
Max protract -min supp
alum S-S
*.537 .623
.016
*.570 .688
.027
*553 .644
.016
*.604 .733
.028
Min swing -min supp
alum S-S
.028 .016
.013
.045 .054
,006
*.370 .442
.012
*.407 .502
.017
Max retract -min supp
Shoe alum S-S
-m!n~.g
Max protract alum -mn supp S,S M ~ p m i t a ~ ::: : i ; i ~ u m :
~i6~0!:
!
ISiS
NL F Coronet Mean SEM *.462 .015 .559
LF Coronet Mean SEM *496 .018 .633
NL R Coronet Mean SEM .425 .026 .470
*.424 ,506 t62
*.452 .551
.389 .369 . 0~i~
'.t36 :::i i
.016 i 0 i 3
.023 ~0i3
;
!~:
.
.016 . . .
L R Coronet Mean SEM *.413 .023 .472
.
.
.400 42!
.018
~016 ~
: :i:i:i
Min swing alum *.2~5 .015 *.299 .025 .287 .014 .255 .015 -rain supp S-S .373 .454 .273 .292 *Significantly different p
Volume 12, Number 6, 1992
379
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,~
Table 5 , Means and standard error of the means of velocity, minimum heights of the lead and nonlead fetlocks and coronets and their respective differences before and after adjustments for velocity. Aluminum Shoe Velocity = Mean 15.19 SEM 0.49 Adjusted mean SEM
L-fet = 6.4 0.4 6.4 0.6
Seattle Shoe ® Mean SEM Adjusted mean SEM
9.0 0.8 9.1 0.6
15.40 0.37
L-cot a 8.6 0.3 8.5 0.3 9.7 0.3 9.7 0.3
L-diff ¢ -2.1 0.5 -2.1 0.7
N-f st f 7.2 0.4 7.1 0.5
-0.7 0.8 -0.6 0.7
8.4 0.5 8.4 0.4
N-corg 8.6 0.4 8.6 0.4
N-diff h -1.4 0.4 -1.5 0.4
9.1 0.5 9.1 0.4
-0.7 0.5 0.7 0.4
ameter/sec; bcentimeters;Cleadfetlock;dleadcoronet;edifference= leadfetlockheightminus lead coronetheight;fnonleadfetlock;=nonleadcoronet;hdifference = nonleadfetlock height minus nonleadcoronet height.
DISCUSSION
Previous studies suggested that decreased overlap times increase the racing performance of horses. 9'1a The increased arcs of flight, seen as a result of the unloading properties of the Seattle Shoe®, did not result in decreases in the overlap times of the limbs of the horses in this study. The velocities of the horses galloping on the straightaway in this study were higher than those reported in an earlier study employing similar methods to examine the kinematics of galloping Thoroughbreds. 13Despite these differences, the values are compatible with the differing speeds because of the interactions demonstrated between velocity and stride length, stride time and the times of the swing and support phases of the stride.9 The weight difference of the Seattle Shoe®had no apparent affect on the timing parameters and stride lengths of these horses, but this may be due to the spring characteristics of the shoes countering the effect of the added weight. The most significant and obvious effects of the Seattle Shoe®on the stride parameters of these six galloping horses occurred in the arcs of flight of the limbs. Horses shod with Seattle Shoes® had significantly greater heights of the carpi, fetlocks and coronets in the protraction portion of the swing phase when galloping. Apparently, the greater recoil imparted to the limb from the spring of the shoe may prolong the return of the limbs to the ground. This may be further supported by the slightly greater swing times and stride times and longer stride lengths seen when these horses were shod with the Seattle Shoes °, even though none of the timing parameters were significantly different between the horses being shod with Seattle Shoes* versus aluminum racing plates. On the average, when the horses were shod with Seattle Shoes~, the fetlock did not drop as far below the coronet as it
380
did with the aluminum shoe during the support phase of the stride. Only once was the fetlock of a horse shod with aluminum shoes observed not to drop to or below the level of the coronet; whereas, when the horses were shod with the Seattle Shoe®, the fetlock remained above the level of the coronet during the phase of total support one-third of the time. From this, it would appear that the Seattle Shoe®is absorbing some of the initial impact force and reducing the strain on the flexor tendons. An earlier study using instrumented shoes found that when the limb was bearing weight and the spring of the Seattle Shoe®was loaded, the impact and peak forces on the ground surface of the shoe increased.a Apercentage of the potential energy normally stored in the suspensory apparatus as the fetlock extends may be stored by the compression of the Seattle Shoe®. The accentuation of the arcs of flight observed with the Seattle Shoe ®may be due to the storage and release of a higher amount of potential energy than the suspensory apparatus of the limb by itself. From the six horses used in this study, it appears that the Seattle Shoe* has no detrimental effects on the performance of the galloping horse. In fact, the Seattle Shoe® may be beneficial in decreasing the fatigue on the suspensory apparatus of the limbs by assisting the actions of the supporting ligaments and tendons that cushion the impact and recycle the energy during rapid locomotion. 7 However, the spring design of the Seattle Shoe ®significantly increases the ares of, flight of the limbs, which requires horses to make kinematic adjustments necessary to maintain their level of performance.
REFERENCES 1. 2.
"Synthetic Flesh" buffers hooves. Equus69:63-64,1983. Are no nails good news? Equus95:36-42,1985.
JOURNAL OF EQUINE VETERINARY SCIENCE
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Table 6 . The minimum heights of the lead and nonlead fetlocks and coronets, their respective differences categorized for use of the chi-square statistic, the chi-square values for the lead, nonlead and combined data, and the area of distribution of the Seattle S h o e (actual values) under the chi-square distribution of the aluminum shoe (expected values). Aluminum Shoe Horse
1 1 12:.::
Heights =
Heights =
L-feP 0.048 0.041
L-cor ¢ 0.064 0.064
01082
: ~01008 0~01-0~025 0.081 0.000 0.089 0.009 0i076 ~0:0;46 ::
2
iO.
3 3 :4
0.089 0.065 0106o11
L-diff d -0.016 -0.054
Category = 3 3 :, 2
N-fet f 0.056 0.043 :: : i01~:,:, :: 0~082 0.066 0.082 i: 0 . 0 8 3
3
1 1 3
i:i:
N-core 0.085 0.052
N-diff h -0.029 -0.039
Category = 3 3 2
0~073 0~:306
~0:~4
0.083 0.091 :i 0~0831
-0.017 -0.009
:
3 3 2
0i000
5 0.061 0.087 -0.017 3 0.061 0.065 -0.004 5 0.058 0.078 -0.025 3 0.086 0.003 -0.016 6 i i0i057i OiO~i i ;010!9 i i ; :.~!:. iOi076 ii i ii~i::i ! i ii0i079::ii i i:.-0i003i i' :. 6 i i i0:0781 :. 0:076 i i i'ii Seattie.Sh0e=........................................................................................................................................................... Horse
Heig hte =
1 1 2
L-feP 0.056 0.089 0~i2t
L-cor c 0.098 0.113 0:305;i
L-diff d -0.042 -0.024 i 0~:O16
0.092 0.080
0.103 0.101
-0.011 -0.021
::
3 3
:
:iO,~i ', i OiO~
::
5 5 6
:
i23 Lead
i2 i;i;21 :
Heights =
i 0~l~i :, :::':i:i : 010~
0.097 0.095 i 0i120!
i
2 3
0.089 0.087 O~
i: Nonlesd
:i-o;03~:
Category = 3 3 :;;:.::;i 3 3
iii~
i i:3i
0.058 0.008 i0~01~ i!
i !0;o2 ::i
1 1 i1 ~
:iiii i:::!
ii i i!
i ! :,i:::!
N-fet ~ 0.092 0.091 i::i0i083ii;
N-cor e 0.069
0.104 0.058
0.108 0.061
i iio:0~i! i i:O~07s :ii i:
0.116
ii i iiii0108~iii
N-diff h 0.023
Category• 1
-0.025
3
:.0~::.i
l i:~
-0.004 -0.003
2 2
::.iii-Oi039i
i:;
0.064 0.076 -0.012 0.088 0.100 -0.012 i ii ! i i; i i:ii;iO~105iiiii~::: ii i:.iii:.::iOi~: i!:i ! ! ili iiiiO:020 ::ii
:ii:i ii i:
i i: !ill i',:iii::iiiio; sili i '.: :i: i':':i
!!il i3i 3 3
i i:.i
ii
i:. ::i: ii:,ii i: iii:iii
Both
Chi-squared 10.0 9.97 18.9 Distribution i =<0.010 =<0.010 =<0.005 ~Yneters bleadfetlock ¢lead coronet ddifference = lead fetlock height - lead coronet height eif difference > or = to O; 2 if difference < 0 and • -0.01; 3 if difference < or = to -0.01 fnonlead fetlock gnonleadcoronet hdiffsrence = non lead fetlock height - nonlead coronet height iValues from 'Tables of the Percentage Points of the X2 -Distribution.: Biometdca,Vo132 (1941), pp.188-189, by Catherine M. Thompson. 3. Balch O, Grant B, Ratziaff M, Wilson P, Mama K, Cannon J: Design, application, testing and use of compressible plastic horse shoes "Seattle Shoes.' Proceedings, Amer Assoc Equine Practnr pp405-418,1989. 4. Cheney J, Shen C, Wheat J: Relationship of racetrack surface to lameness in the Thoroughbred racehorse. Amer J Vet Res 34:1285-1289,1973. 5. Forfay T: Glue-On shoe, Pour-On pad offer pliable protection. Equus 115:23-26,1987. 6. Grant BG, Balch O, Ratzlaff MH, Cannon J: The application and use of compressible plastic horseshoes - Seattle shoes. Equine Pract 7:18-27,1989. 7. Hildebrand M: Mechanics of horse legs. Amer Scientist 75(6):594-601,1987. 8. Kilby E: The hoof-pad explosion: will your horse benefit from the fancy footwork? Equus 82:38-41,73-75,82,1984. 9. Pratt G: Remarks on gait analysis. In Equine ExerPhysiol Ed. D. H. Snow, S. Persson and J. Rose. Burlington Press: CamVolume 12, Number 6, 1992
bridge, pp245-262,1983. 10. Pratt GW: Racing surfaces - a survey of mechanical behavior. Proceedings, Amer Assoc Equine Practnr, 30:321331,1984. 11. Ratzlaff MH, Shindell RM, White KK: The interrelationships of stride lengths and stride times to velocities of galloping horses. J Equine Vet Sci 5:283-297,1985. 12. Ratziaff MH, Grant BD, Frame JM, Hyde ML: Locomotor forces of galloping horses. Proceedings 2nd Internat'l Conf on Equine Exer Physiol, pp574-586,1986. 13. RooneyJ, Genovese R: A survey and analysis of bowed tendon in thoroughbred racehorses. JEquine VetSci 1:49-53,1981. 14. Sparks JM: Prevention of lameness in horses. Proceedings, 15 Annual meeting Assoc Equine Practnr, pp67-73,1970. 15. Zebarth BJ, Sheard RW: Impact and shear resistance of turf grass racing surfaces for Thoroughbreds. Amer J Vet Res 46:778-784,1985.
381
' "~:~: " ~
Refereed
THE EFFECTSOF A COMPRESSIBLEPLASTICSHOE - THE SEATTLESHOE®ON THE KINEMATICSOF THE STRIDESOF GALLOPING THOROUGHBRED HORSES Patrick D. Wilson, MS, DVM;a Marc H. Ratzlaff, DVM, PhD;1 Barrie D. Grant, DVM, MS; 2 Martha L. Hyde, PhD;1 and Olin K. Balch, DVM, MS1
SUMMARY
This study was undertaken to determine if the kinematic parameters of galloping horses were altered when these horses were shod with Seattle Shoes®. Analyses of films of six Thoroughbred horses galloping through a track straightaway, with and without Seattle Shoes®, were used to determine velocity, stride length, stride time, swing time and support time ofthelimbs, the percentages of the stride time spent in the swing and support phases, and the arcs of flight of the carpi and fetlocks of the forelimbs and the coronets of all four limbs. Descriptive statistics were calculated for each of these variables. Comparisons were made between those measured from horses shod with and without the Seattle Shoe ®,usingboththe paired-t test and analysis of covariance, which eliminated the influence of differing velocities. No significant differences occurred in the stride lengths or timing parameters when these Authors' address: 1Departmentof Veterinary and Comparative Anatomy, Pharmacology and Physiology, Department of Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman,WA 99164; 2SanLuis Rey Equine Clinic, 4211 Holly Lane, Bonsall, CA 92003; 3Departmentof Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, "IX 77843. Address correspondenceto Dr. Ratzlaff. Acknowledgments: This study was supported by Kinesis, Inc., Salem Oregon. the assistance provided by Jane Koepcke, Lisa Wood and Marry Bennett is greatly appreciated.
374
horses were shod with Seattle Shoes®. The Seattle Shoe ®had it's most significant effect on the arcs of flight of the limbs. The compression of the Seattle Shoe ®appears to store a portion of the potential energy normally stored in the suspensory apparatus and results in a decreased extension of the fetlock. This energy is then released, causing significant increases in the heights of the forelimb during retraction and protraction. Although kinematic adjustments are required by horses to maintain the level of performance, the Seattle Shoe®appears to have no detrimental effects on the performance of galloping horses and it may decrease strain on the suspensory apparatus.
INTRODUCTION
There has been a long-standing interest in providing athletic horses with the proper footwear to both increase performance and to prevent or treat lameness. Hoof pads inserted between the shoe and the hoof have been used for sole p~otection, shock absorption, and for accentuating the action of gaited horses. 1,8 The greatest disadvantage of the use of hoof pads is the tendency for the shoe to move in response to the compression of the pad which loosens the nails and results in greater damage to the hoof wall. "Nailless" shoes and "Pour-On" pads have gained popularity for the prevention of problems arising from excessive hoof wear and as a treatment for lameness,a,s Reports indicate that of all the footwear
JOURNAL OF EQUINE VETERINARY SCIENCE
:iii•~iii~i
Figure 1.
The Seattle Shoe® prototype used in this study.
A. Ground surface with metal wear rim removed. 1 = shelf for nail holes, 2 = thread hole for attachment of wear rim.
Figure l B . Ground surface with aluminum wear rim.
designed for use in horses, only two have been tested scientifically to determine the effects on the performance of the horse. These are the Budkirk Nature Plate®and the Seattle Shoe*. The Budldrk Nature Plate* was designed to be a "natural" extension of the hoof with the intention of maintaining the normal angles and configuration of a physiologically normal hoof.14 This shoe was reported to be a valuable adjunct in the treatment of lamenesses. TMThe disadvantage of the Budkirk Nature Plate* is the careful foot preparation and fitting required for optimum results. The Seattle Shoe* has been shown to be a valuable adjunct in the treatment of museuloskeletal lamenesses. 3,6 This shoe was designed with a compressible, hourglassshaped spring to absorb and store the energy of the impact force and return it to the limb. The effects of the Seattle Shoe* on the concussive forces experienced by the limbs, and the effects of the spring design on locomotion have not been reported. The desired effects of the Seattle Shoe* would be to absorb the impact force and decrease the strain on the suspensory apparatus of the fetlock, similar to a track with a loose cushion and soft, pliant base.l°.12.16Instead of a reduced recoil or "rebound energy" of the limb as Cheney et al.4 observed on such a surface, the impact force would be stored in the shoe and released, creating greater recoil of the limb and greater efficiency of the stride. This study was undertaken to determine if any alterations in the timing components or arcs of flight of the limbs of galloping horses were present when these horses were shod with Seattle Shoes*, when compared to being shod with standard aluminum racing plates.
=Delrin,DupontCompany,Wilmington, Delaware.
Volume 12, Number 6, 1992
Figure 1 C . Side view without the metal wear rim. 1 = toe clip on foot surface.
METHODS AND MATERIALS
The Seattle Shoes* used in .this study were machined from an acetal resin a and consisted of two plates connected by an hourglass-shaped spring (Fig. 1). The foot plate, the portion that lies adjacent to the hoof, had lateral and medial shelves for the placement of nail-holes. Four screw holes in the ground plate allowed for the attachment of wear rims, which were milled from aluminum. The shoes measured 3.8 centimeters in thickness when nonweight bearing, 2.8 centimeters when fully compressed, and weighed 310 to 325 grams. The aluminum racing plates used as the control weighed 76 to 85 grams. Six clinically sound Thoroughbred horses, undergoing a daily training regimen of one mile at a trot followed by one mile at a gallop, were used in this study (Table 1). Side view movies were taken of each horse with a high speed 16mm camera b positioned perpendicular to and 30 meters from the running line. Each horse was photographed with black and white filmc at a speed of 300 frames per second as it galloped through the straightaway. Each horse was shod with either standard aluminum racing plates or with Seattle Shoes* and therefore, served as its own control. After being shod, at least three days of regular work-outs were allowed for the horses to become accustomed to the shoes before filming. The skin over specific sites of each limb were marked with one-half inch dots of white cosmetic paste, d These sites were the lateral and medial collateral ligaments of the carpus at the level of the middle carpal joint, the center of rotation of the metacarpophalangeal (fetlock)joints, and the lateral and medial sides of the coronet on all four limbs. The inside rail and posts of the track were removed to allow unobstructed visualization of the horses. White lime 375
....i~i!~!~!iii~iiii~iiiiii~;ii~ZZ::~ ............ i~i!~iiiiiiiii~ii~i!iii~W~ii!~..............
•
•
%
%~.
#
Table 1, Signalment of horses. Horse
Age =
Breed n
Sex =
Weight a
1 2 3 4 5 6
4 7 7 11 3 3
TB TB TB TB TB TB
G G G F F F
1150 1125
1050 1005
850 925
=years bTB=Thoroughbred CG=geldodmale; F=female
dpounds
was used to mark a running line on the track four meters from the inside rail on the straightaway. Five reference markers were filmed: Two reference stakes were placed on the running line 5.0 meters apart, two reference stakes were placed directly behind these stakes on the outside rail and a post with 0.5 meter gradations was centered between the two stakes on the running line. After filming these reference markers, the two stakes on the running line were removed and the post was centered between the two stakes on the outside rail. The stakes and post were then left in position on the outside rail to provide reference distances during filming of the horses. On the days of filming, the horses were trotted one mile followed by two 3/16th mile gallops which transversed the straightaway during the final 1/8th mile. The horses were filmed at this time. The horses were walked and trotted for 10 minutes between each trial. The f'dms of two consecutive strides were analyzed ~ frame by frame to determine the stride length, timing parameters, velocity and the arcs of flight of the carpi, fetlocks and coronets. The timing parameters included swing time, support time, stride time, and individual limb overlap times. The heights of the carpi, fetlocks and coronets at hoof contact, maximum support, hoof lift, and during retraction and protraction were measured from the arcs of flight. Retraction is defined as the portion of the swing phase where the limb is lifted, or retracted from the ground, and protraction is the portion of the phase where the limb is extended forward and returns to the ground. The swing phase of the limbs were further characterized by calculating the differences between the maximum heights of the carpi, fetlocks and coronets at retraction and protraction with these heights during maximum support and the minimum heights during the swing phase. Additionally, the differencesbetween the minimum heights of bModelIPL, PhotoSonicsCorporation,Burbank, California. ¢Tri-X7278, EastmanKodakCompany,Rochester,New York. dCIownWhite, Ben Nye Makeup, Inc,, Los Angeles, California.
376
the carpi, fetlocks and coronets during the swing phase and these heights during maximum support were determined. Subtracting the heights of the various points on the limb during the swing phase with their heights at maximum limb support was used to compensate for the difference in the height of the Seattle Shoe*. Stride lengths for each limb were also measured directly from the track by averaging the distance between contact of each hoof from four successive strides. Descriptive statistics (mean, standard error of the mean, and coefficient of variation) were calculated for each variable. A paired-t test was used to compare the values of each variable measured when the horses were shod with the Seattle Shoe ® versus the aluminum racing plates. The General Linear Procedure of the SAS Analysis of Covarience was used to eliminate the influence of the differing velocities on each of the stride parameters and to obtain the adjusted means and the standard error of the mean. In this procedure, the variation in velocities between horses was eliminated and the data was adjusted using velocity as a covariant. During the support phase of each limb, the minimum height of the coronet was subtracted from the minimum height of the fetlock. Because of the relatively large standard deviation of the resulting differences, the chi-square test was implemented, categorizing the values ofx >O as 1, O >x>-0.01 as 2, and x <-0.01 as 3. A significance level of p<0.05 (a<0.05 for chi-square) was used for all statistical procedures. Emphasis was placed on the timing parameters and on those variables related to the arcs of flight of the limbs that were significantly different when the horses were shod with the Seattle Shoes® versus the aluminum racing plates, after making adjustments for differing velocities. The absolute arcs of flight are those measurements made from the ground to the marked point on the limb. The relative arcs of flight are the same measurements relative to the height of these points at the middle of the support period of the limb (Fig. 2).
RESULTS The velocity, timing parameters (stride time, average litnb support and swing times, the percent of the stride times spent in the support and swing phases, and the ratios of the support time to the swing time) and the stride lengths were not significantly altered by the Seattle Shoe* (Table 2). The absolute arcs of flight of the carpi were higher in these horses when shod with the Seattle Shoe® (Table 3). The carpi of both the lead and nonlead limbs were significantly higher during maximum limb support and protraction; the
JOURNAL OF EQUINE VETERINARY SCIENCE
.... ~ ! ; . . - %
A 1.2 1.0
Carpus
0.8 0.6
o.,I o.~r . DISTANCE
l
-- 8E.CILE ~ O E I HOOF~
.__j
t ;~OOFutw .......... ;'" .
.
.
.
.
. . . . . . . . . . . . . . . . . . . . . .
.
.
.
.
.
.
"-..
"-..
.......... ""
.
¢/) 1.o Fetlock nl O.4
f
q
t.-------'=--"
...................................................................
1OIc°r°net 0.8 0.6
B
.
0.4 0.2 0
....................................................................
~ '
o
-.
~"--~" '
1
'
2
'
3
'
4
'
5
±
6
METERS
Figure 3. Arcs of flight of the carpus, DISTANCE
Figure 2.
fetlock and coronet of horse 3 galloping at similar velocities when shod with Seattle Shoes ® and with aluminum racing plates.
Methods for measurements from the arcs of flight
point on the limb (carpus) ~ = hoof contact, 1' = hoof lift. ~ •a Measurement of actual values. 1 = minimum height during full support, 2 = height at hoof lift, 3 = maximum height of retraction, 4 = minimum height during swing phase, 5 =
maximum height of protraction and 6 = height at hoof contact. B . Measurement of the relative heights, a = maximum height of retraction minus minimum height during full support, b = maximum height of retraction minus minimum height during swing phase, c = maximum height of protraction minus minimum height during full support, d = maximum height of protraction minus minimum height during swing phase, • = minimum height during swing phase minus minimum height during full support.
minimum height during the swing phase was significantly higher in the lead carpus; and the height of the lead carpus was significantlyhigher at the time of hoof contact. The differences in the arcs of flight of the carpus, fetlock and coronet of the lead forelimb of one of the horses when shod with aluminum racing plates and when shod with Seattle Shoes®are illustrated in Figure 3. The relative arcs of flight of the carpi were lower during retraction of the limb when shod with the Seattle Shoe®, but higher throughout the rest of the swing phase (Table 7). The elevation of the lead carpus was significantly lower during retraction and the descent of that carpus to the minimum swing phase height was also less. The elevation of both carpi from the minimum swing height to the maximum height of protraction were significantly higher with the Seattle Shoe®. The absolute heights of the fetlocks were higher throughout the arcs of flight for the horses st.od with the Seattle Shoe ® (Table 3). The fetlocks of both the lead and nonlead limbs
Volume 12, Number 6, 1992
were significantly higher at the maximum heights of retraction, the minimum heights during the swing phase, and the maximum heights at protraction. The height of the lead fetlock was significantly higher during total limb support. The relative heights of both the lead and nonlead fetlocks of the six horses shod with Seattle Shoes ®were significantly higher throughout the swing phase of the limb with a significantly smaller descent from the height of retraction to the minimum height of the swing phase (Table 4). However, this descent of the lead fetlock was not significant after adjusting for velocity. The absolute heights of the coronets of the front limbs were higher throughout the flight of the limbs when these horses were shod with the Seattle Shoe®(Table 3). The heights of the coronets of the lead front limb were significantlygreater at the times of hoof contact, hoof and limb support. The coronets of both the lead and nonlead front limbs were significantly higher at the maximum heights of retraction, the minimum heights of the swing phase and the maximum heights of protraction. The relative heights of the coronets of the lead and nonlead front limbs of the horses shod with Seattle Shoes® were significantly greater at the maximum height of retraction, the minimum height of the swing phase and at the maximum height of protraction (Table 3), with a significantly smaller rise of the lead front coronet from the minimum height of the swing phase to the maximum height of protraction (Table 4). When the horses were shod with aluminum racing plates, the fetlocks of the nonlead limb dropped twice as far below the
377
.: ..~:
~ ~ ..............
!".~
...............
Table 2 . The means, standard error of the means and significance of the velocities, stride lengths and stride timing parameters before and after adjustments for velocity. Parameter Velocity
Shoe" alum
(m/sec)
S-S
:iii iiii !i!:i
Mean 15.2
Range 11.6-16.8
SEM .488
CV 11.1
15.4
11.9-16.9
.370
8.33
i ii !!i
iiiii:i
!:! : ? ?i
iiiil ! i::
i i iiii
.414
.370-.497
.009
7.31
(see)
S-S
.412
.376-.475
.008
6.72
ii::i:~ill~ i ::!
~~ 5;~;i 28
.306 .306
.268-.360 .271 -.347
Swing time
alum S-S
(sec)
itim~i:11: : i[:
% Support time
%s~g time !!
Si
i
i i i i::iS~S
i:ii:;i:;::iL345:::
::::
::i:
alum S-S
26.0 25.6
H u m :. sis
!
i:::
i!:: ii~OO8
i + i
24.4-27.8 23.3-28.3
: ::74~0 ! i~4i4
NS
.003 .004
::i72~4.~75i6; 7!:~7-76;7 i
!i003: !i
i i!::i :i
6.85 7.05
;1!
i::
4.22 5.80 i :I~43: i.95!: !:
.412
.005
NS
.414
ii:. i 8~46!iii .006 .006
Slg c
NS
...........
alum
!:i
Adjusted Sem
Mean
!~ii! i:i : i i :h:::::::::::::
Stride time
(s~)! !:;i
Slg c
NS
~;
iii:i !ii: i
;
iili .305 .308
::::.::1:. ! NS
.005 .
::ii NS
:.:::::.~346: i i:: : :.i::ii : : : : i l t 26.0 25.7
NS::
.003
NS
! i:. ! i003 :
N8: :::::
.002
NS
Overlap Tlmes b (sec)
NR-LR
::: NR-NF
alum S-S
.044 .044
:. :ii:::ii!:S ! S
:~0~
alum S-S
.005 .002
0-.034 0-.018
.004 .002
~022
::i008:~.04.0
:i :: : i022:i::.:: : .
.002 .002
0-.016 0-.018
.002 .002
i LR-LF
alum S-S aalum = aluminum racing plate S-S = Seattle Shoe ® bNR = nonlead rear limb LR = lead rear limb NF = nonlead front limb LF = lead front limb "NS = not significant, p>0.05
i
.037-.053 .034-.056 :
.001 .002
NS
0I i~ii i:
.044 .044 ::
coronets on the average than they did when shod with Seattle Shoes® and the fetlocks of the lead limb dropped more than three times as far on the average than they did with the Seattle Shoe® (Table 5). The relatively large standard deviations made the paired t-test invalid for statistical analysis of the significance of these differences. The chi-squared analysis, however, showed the distribution of these values to be significantly different (Table 6). When the horses were shod with Seattle Shoes®, the maximum height of retraction and the minimum height during
378
10.1 14.2
235 255
NS
::: 239 347
NS
! !::ii: ii04:i:. :: :.!:: : : i i: .005 .003 : ii::::;ii:::: : :~023 i .002 .002
,001 .003 i:023 :~:~:~::~i .001 .002
NS
~i:~ NS
the swing phase of the lead rear coronet were significantly higher (Table 3). After adjusting for velocity, the relative height of retraction of the lead rear coronet was no longer significantly different between the two shoes (Table 4). No significant differences were seen in the heights of the coronet of the nonlead rear limb when the horses were shod with Seattle Shoes®versus aluminum racing plates (Tables 3 and 4).
JOURNAL OF EQUINE VETERINARY SCIENCE
......... ~~i~i~..... ,~
•
.~.".~........... [~.
,~!;: .....
. ~ t "~*'~i~"~¢:~ ~ .~. . . . . . . .
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Table 3 . T h e m e a n s a n d standard error of the m e a n s of the heights (in meters) of the arcs of flight v a r i a b l e s after adjustments for velocity.
Hoof contact
Hoof lift
NL Carpus Mean SEM .483 O.15 .520
Shoe alum S-S
M~i~Om
alum S-S ~u~ :
.493 .507 505
Minimum swing
alum S-S
.406 .429
p~i~a~ion:, i
~.:~S~Si.
Hoof contact
Shoe alum S-S
:
:s;s
:
L Carpus Mean SEM *.462 .012 .515
.011 : 10i3 .013
~::.:.i!:!~
~:
: :i:;09! :!
.011
*.420 ,470
.009
~
SiS
Minimum alum swing S: S M~mOm i alum i : ; p~ra~i~ ::~S~S *Significantly different p<0.05.
*.349 .464 '51i
::
:i01~ i
.245 .273 i*:5~ ii
.013
*.471 ,593
,144
,013
:::::.: :.728:ii i:
ili
~i2~ ::~:ii : :
NL R Coronet Mean SEM .132 .006 ,131
i: :::io97ii:.
alum .118 .005 *.115 S-S .132 .131 Maximum .......................alum ............................. 5 ~ .................0 t 5 ................. ~58
L Fetlock Mean SEM .209 .013 .235
.011
*,441 ,527
LF Coronet Mean SEM *.122 .006 ,143
Hoof lift
re!!~ ~
.254 .271 ~15~7!
!i11:
NL F Coronet Mean SEM .124 .007 ,134
~
.502 .526 :: ! ~510!
NL Fetlock Mean SEM .200 .011 .232
L R Coronet Mean SEM .146 .007 ,136
i ~ 8 i i iili:i
ii:i
:.:i:ii
.005
.134 .007 .136 .006 .123 .133 , !9 ........ .......... : 5!6 .........., ~ 2 ................... .............5 ~ : ::: : ~ 0 2 6
.016 *.384 .026 .378 .015 *.348 .018 . . . . . . . . . . . . . . . . . . . '.552 .....................................:366 ........................................ ~4~ . . . . . . . . 019:i. *,538 0 2 8 :~81 ~017: 017: ::: i ~6~: iii ~:: ~: ~.:: :::.~7:1 i:~.: ~i i i:i:: iS:}! ::i:
Table 4, The m e a n s a n d standard error of the m e a n s of the relative heights (in meters) m e a s u r e d from the arcs of flight (see Figure 2) after a d j u s t m e n t s for velocity.
NL Carpus L Carpus NL Fetlock Shoe Mean SEM Mean SEM Mean SEM Max retract alum .I 19 .012 *.135 .005 *446 0.10 - m n supp S-S .097 .I 17 .490 Max retract:: i:i:ii ii :alum: .............:.:.: ,091:.: : :..:~,008 :.::: : : : : : , . :,090: :: :: ~007 ::. :.: ....::: ::: . : :,0 : ::
L Fetlock Mean SEM *.475 .013 .542 ,:::,.:.: ::............... 068.: ............O!0 ....
Max protract -min supp
alum S-S
*.537 .623
.016
*.570 .688
.027
*553 .644
.016
*.604 .733
.028
Min swing -min supp
alum S-S
.028 .016
.013
.045 .054
,006
*.370 .442
.012
*.407 .502
.017
Max retract -min supp
Shoe alum S-S
-m!n~.g
Max protract alum -mn supp S,S M ~ p m i t a ~ ::: : i ; i ~ u m :
~i6~0!:
!
ISiS
NL F Coronet Mean SEM *.462 .015 .559
LF Coronet Mean SEM *496 .018 .633
NL R Coronet Mean SEM .425 .026 .470
*.424 ,506 t62
*.452 .551
.389 .369 . 0~i~
'.t36 :::i i
.016 i 0 i 3
.023 ~0i3
;
!~:
.
.016 . . .
L R Coronet Mean SEM *.413 .023 .472
.
.
.400 42!
.018
~016 ~
: :i:i:i
Min swing alum *.2~5 .015 *.299 .025 .287 .014 .255 .015 -rain supp S-S .373 .454 .273 .292 *Significantly different p
Volume 12, Number 6, 1992
379
....~ i i ~ ~~ ~ H ~ , ,..~~i:~:%~ :!~i "%. =:= ,:=======================
,~
Table 5 , Means and standard error of the means of velocity, minimum heights of the lead and nonlead fetlocks and coronets and their respective differences before and after adjustments for velocity. Aluminum Shoe Velocity = Mean 15.19 SEM 0.49 Adjusted mean SEM
L-fet = 6.4 0.4 6.4 0.6
Seattle Shoe ® Mean SEM Adjusted mean SEM
9.0 0.8 9.1 0.6
15.40 0.37
L-cot a 8.6 0.3 8.5 0.3 9.7 0.3 9.7 0.3
L-diff ¢ -2.1 0.5 -2.1 0.7
N-f st f 7.2 0.4 7.1 0.5
-0.7 0.8 -0.6 0.7
8.4 0.5 8.4 0.4
N-corg 8.6 0.4 8.6 0.4
N-diff h -1.4 0.4 -1.5 0.4
9.1 0.5 9.1 0.4
-0.7 0.5 0.7 0.4
ameter/sec; bcentimeters;Cleadfetlock;dleadcoronet;edifference= leadfetlockheightminus lead coronetheight;fnonleadfetlock;=nonleadcoronet;hdifference = nonleadfetlock height minus nonleadcoronet height.
DISCUSSION
Previous studies suggested that decreased overlap times increase the racing performance of horses. 9'1a The increased arcs of flight, seen as a result of the unloading properties of the Seattle Shoe®, did not result in decreases in the overlap times of the limbs of the horses in this study. The velocities of the horses galloping on the straightaway in this study were higher than those reported in an earlier study employing similar methods to examine the kinematics of galloping Thoroughbreds. 13Despite these differences, the values are compatible with the differing speeds because of the interactions demonstrated between velocity and stride length, stride time and the times of the swing and support phases of the stride.9 The weight difference of the Seattle Shoe®had no apparent affect on the timing parameters and stride lengths of these horses, but this may be due to the spring characteristics of the shoes countering the effect of the added weight. The most significant and obvious effects of the Seattle Shoe®on the stride parameters of these six galloping horses occurred in the arcs of flight of the limbs. Horses shod with Seattle Shoes® had significantly greater heights of the carpi, fetlocks and coronets in the protraction portion of the swing phase when galloping. Apparently, the greater recoil imparted to the limb from the spring of the shoe may prolong the return of the limbs to the ground. This may be further supported by the slightly greater swing times and stride times and longer stride lengths seen when these horses were shod with the Seattle Shoes °, even though none of the timing parameters were significantly different between the horses being shod with Seattle Shoes* versus aluminum racing plates. On the average, when the horses were shod with Seattle Shoes~, the fetlock did not drop as far below the coronet as it
380
did with the aluminum shoe during the support phase of the stride. Only once was the fetlock of a horse shod with aluminum shoes observed not to drop to or below the level of the coronet; whereas, when the horses were shod with the Seattle Shoe®, the fetlock remained above the level of the coronet during the phase of total support one-third of the time. From this, it would appear that the Seattle Shoe®is absorbing some of the initial impact force and reducing the strain on the flexor tendons. An earlier study using instrumented shoes found that when the limb was bearing weight and the spring of the Seattle Shoe®was loaded, the impact and peak forces on the ground surface of the shoe increased.a Apercentage of the potential energy normally stored in the suspensory apparatus as the fetlock extends may be stored by the compression of the Seattle Shoe®. The accentuation of the arcs of flight observed with the Seattle Shoe ®may be due to the storage and release of a higher amount of potential energy than the suspensory apparatus of the limb by itself. From the six horses used in this study, it appears that the Seattle Shoe* has no detrimental effects on the performance of the galloping horse. In fact, the Seattle Shoe® may be beneficial in decreasing the fatigue on the suspensory apparatus of the limbs by assisting the actions of the supporting ligaments and tendons that cushion the impact and recycle the energy during rapid locomotion. 7 However, the spring design of the Seattle Shoe ®significantly increases the ares of, flight of the limbs, which requires horses to make kinematic adjustments necessary to maintain their level of performance.
REFERENCES 1. 2.
"Synthetic Flesh" buffers hooves. Equus69:63-64,1983. Are no nails good news? Equus95:36-42,1985.
JOURNAL OF EQUINE VETERINARY SCIENCE
~:: ~1 ~::~ ". ~,~4~" : ~ " . ~.
:.
~ ~ ~~ :~ ~ ,~,.~
Table 6 . The minimum heights of the lead and nonlead fetlocks and coronets, their respective differences categorized for use of the chi-square statistic, the chi-square values for the lead, nonlead and combined data, and the area of distribution of the Seattle S h o e (actual values) under the chi-square distribution of the aluminum shoe (expected values). Aluminum Shoe Horse
1 1 12:.::
Heights =
Heights =
L-feP 0.048 0.041
L-cor ¢ 0.064 0.064
01082
: ~01008 0~01-0~025 0.081 0.000 0.089 0.009 0i076 ~0:0;46 ::
2
iO.
3 3 :4
0.089 0.065 0106o11
L-diff d -0.016 -0.054
Category = 3 3 :, 2
N-fet f 0.056 0.043 :: : i01~:,:, :: 0~082 0.066 0.082 i: 0 . 0 8 3
3
1 1 3
i:i:
N-core 0.085 0.052
N-diff h -0.029 -0.039
Category = 3 3 2
0~073 0~:306
~0:~4
0.083 0.091 :i 0~0831
-0.017 -0.009
:
3 3 2
0i000
5 0.061 0.087 -0.017 3 0.061 0.065 -0.004 5 0.058 0.078 -0.025 3 0.086 0.003 -0.016 6 i i0i057i OiO~i i ;010!9 i i ; :.~!:. iOi076 ii i ii~i::i ! i ii0i079::ii i i:.-0i003i i' :. 6 i i i0:0781 :. 0:076 i i i'ii Seattie.Sh0e=........................................................................................................................................................... Horse
Heig hte =
1 1 2
L-feP 0.056 0.089 0~i2t
L-cor c 0.098 0.113 0:305;i
L-diff d -0.042 -0.024 i 0~:O16
0.092 0.080
0.103 0.101
-0.011 -0.021
::
3 3
:
:iO,~i ', i OiO~
::
5 5 6
:
i23 Lead
i2 i;i;21 :
Heights =
i 0~l~i :, :::':i:i : 010~
0.097 0.095 i 0i120!
i
2 3
0.089 0.087 O~
i: Nonlesd
:i-o;03~:
Category = 3 3 :;;:.::;i 3 3
iii~
i i:3i
0.058 0.008 i0~01~ i!
i !0;o2 ::i
1 1 i1 ~
:iiii i:::!
ii i i!
i ! :,i:::!
N-fet ~ 0.092 0.091 i::i0i083ii;
N-cor e 0.069
0.104 0.058
0.108 0.061
i iio:0~i! i i:O~07s :ii i:
0.116
ii i iiii0108~iii
N-diff h 0.023
Category• 1
-0.025
3
:.0~::.i
l i:~
-0.004 -0.003
2 2
::.iii-Oi039i
i:;
0.064 0.076 -0.012 0.088 0.100 -0.012 i ii ! i i; i i:ii;iO~105iiiii~::: ii i:.iii:.::iOi~: i!:i ! ! ili iiiiO:020 ::ii
:ii:i ii i:
i i: !ill i',:iii::iiiio; sili i '.: :i: i':':i
!!il i3i 3 3
i i:.i
ii
i:. ::i: ii:,ii i: iii:iii
Both
Chi-squared 10.0 9.97 18.9 Distribution i =<0.010 =<0.010 =<0.005 ~Yneters bleadfetlock ¢lead coronet ddifference = lead fetlock height - lead coronet height eif difference > or = to O; 2 if difference < 0 and • -0.01; 3 if difference < or = to -0.01 fnonlead fetlock gnonleadcoronet hdiffsrence = non lead fetlock height - nonlead coronet height iValues from 'Tables of the Percentage Points of the X2 -Distribution.: Biometdca,Vo132 (1941), pp.188-189, by Catherine M. Thompson. 3. Balch O, Grant B, Ratziaff M, Wilson P, Mama K, Cannon J: Design, application, testing and use of compressible plastic horse shoes "Seattle Shoes.' Proceedings, Amer Assoc Equine Practnr pp405-418,1989. 4. Cheney J, Shen C, Wheat J: Relationship of racetrack surface to lameness in the Thoroughbred racehorse. Amer J Vet Res 34:1285-1289,1973. 5. Forfay T: Glue-On shoe, Pour-On pad offer pliable protection. Equus 115:23-26,1987. 6. Grant BG, Balch O, Ratzlaff MH, Cannon J: The application and use of compressible plastic horseshoes - Seattle shoes. Equine Pract 7:18-27,1989. 7. Hildebrand M: Mechanics of horse legs. Amer Scientist 75(6):594-601,1987. 8. Kilby E: The hoof-pad explosion: will your horse benefit from the fancy footwork? Equus 82:38-41,73-75,82,1984. 9. Pratt G: Remarks on gait analysis. In Equine ExerPhysiol Ed. D. H. Snow, S. Persson and J. Rose. Burlington Press: CamVolume 12, Number 6, 1992
bridge, pp245-262,1983. 10. Pratt GW: Racing surfaces - a survey of mechanical behavior. Proceedings, Amer Assoc Equine Practnr, 30:321331,1984. 11. Ratzlaff MH, Shindell RM, White KK: The interrelationships of stride lengths and stride times to velocities of galloping horses. J Equine Vet Sci 5:283-297,1985. 12. Ratziaff MH, Grant BD, Frame JM, Hyde ML: Locomotor forces of galloping horses. Proceedings 2nd Internat'l Conf on Equine Exer Physiol, pp574-586,1986. 13. RooneyJ, Genovese R: A survey and analysis of bowed tendon in thoroughbred racehorses. JEquine VetSci 1:49-53,1981. 14. Sparks JM: Prevention of lameness in horses. Proceedings, 15 Annual meeting Assoc Equine Practnr, pp67-73,1970. 15. Zebarth BJ, Sheard RW: Impact and shear resistance of turf grass racing surfaces for Thoroughbreds. Amer J Vet Res 46:778-784,1985.
381