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The purpose of this study was to assess if there was any kinematic differences in the flexion angle of the carpus between horses wearing sports boots and exercise bandages and horses with bare forelimbs while trotting. The hypothesis of the study was that there would be a significant difference in peak flexion angle of the knee between horses with boots, bandages and untreated limbs. Kinematic data was collected from six horses in this study. The horses had a mean weight of 565.1 + 57.3 kg, age of 10.0 + 3.2 years. Reflective markers were placed on the lateral aspect of the elbow, carpal, and metacarpophalangeal joints of the left and right forelimbs. Horses were filmed while trotting in a straight, level path across a sandy surface while wearing sports boots, again while wearing an exercise polo bandage and again with the limbs untreated.
Kinematic data was evaluated for the forelimb knee joint angles. Peak flexion of the forelimb knee joints were evaluated as parameters. A one-way ANOVA was performed to determine whether or not there were any differences on the forelimb peak flexion angle of the knee
joint for each of the treatments. The results of this study indicated that there was no significant difference in peak flexion of the knee joint between the three treatments. This study provides basic kinematic data that documents the differences in the peak flexion angle of the carpus of horses at the trot.
Anatomy of the equine carpus
The equine carpus (knee) is a compound diarthrodial joint (Skiöldebrand, 2004) interposed between the two columns of the antebrachium and the metacarpus. It consists of six to eight short bones which are arranged in two rows (proximal and distal). Four of these bones make up the proximal row of which three (radial carpal, intermediate carpal, ulnar carpal) are axially weight bearing (Colahan et al. 1988). The fourth bone (accessory carpal) is a non-weight bearing bone (Skiöldebrand, 2004).
The other four bones (first carpal, second carpal, third carpal and fourth carpal) make up the distal row of the equine carpus. The cuboidal third carpal bone is the largest of the carpal bones of the distal row and is a major weight bearing
bone (Secombe et al. 2002).
Flexion of the carpal joint
The basic biomechanics of any joint involves three particular planes of transitional motion, medial to lateral, dorsal to palmar or planter, and proximal to distal with rotational motion possible about each plane (Simon and Radin, 1993). The equine carpal joint has two wide collateral ligaments made of strong bands of collagen (Floyd and Mansmann, 2007) connecting the radius and the metacarpus and studies have shown (Colahan et al. 1988; Leach and Dyson, 1988) that instantaneous centre of rotation for limb joints is associated with the location of these collateral ligaments. When the horse is in the swing phase of the stride the knee flexes in order to reduce the moment of inertia (Johnston et al. 1997), decrease the energy requirements for moving the limb as it is protracted (Wickler et al. 2004) thus minimizing drag and maximizing angular acceleration(Palmar et al. 1987) . Kinematics analysis
Kinematic analysis measures the geometry of locomotion or the changes in the position of the body segments in space during a specified time without considering the forces that cause the
locomotion (Barrey, 1999).
At the present time, most of the kinematic evaluations are performed in two-dimensional in the sagittal plane using videographic systems made up of hardware and software components (Vilar et al. 2008). Measuring the equine limb movement in the sagittal plane gives two-dimensional kinematic analyses of the knee joint flexion and extension angles. This is a reasonable simplification as the joints of horses have evolved to swing mainly in this plane as an energy-saving mechanism (Miro et al. 2009). The equine carpal joint kinematics have been studied at the trot (Miro et al. 2009; Valera et al. 2008; Miro et al. 2006; Lanovaz et al. 1999; Johnston et al. 1997; Back et al. 1995; Ratzlaff et al. 1982), however, we were not aware of any studies assessing the differences in knee kinematics at the trot between horses exercised in bandages, those wearing boots and horses exercised with bare limbs. The aim of this study therefore, was to determine the kinematic differences between these three treatments on the peak flexion angle of the knee at the trot. Bandages and boots Bandages were developed out of the need
for wound care, rehabilitation, and safety in transportation (Gomez and Hanson, 2005), and are made from various materials and include dressings, shipping bandages, polo wraps and athletic tapes. The use of bandages is very common in the sports horse especially during exercise. Bandaging is also used to prevent abrasion as well as for support purposes (Morlock et al, 1994). Boots are thought to be useful during training and competition. One study by Balch et al. (1998) into the energy absorption capacity of equine boots found that boots are useful for supporting the fetlock as they reduce fetlock hyperextension. In an experiment with 26 horses wearing four different types of support boots, Kicker et al. (2004) found that all boots reduce maximum extension of the fetlock and tension on the superficial digital flexor tendon compared to the untreated limb. This study also suggested this might have an adverse affect on the fibre alignment if used over a long period of time. Sanders (2009), however, found that boots and bandages did not cause a significant reduction in peak fetlock extension; however, their results also showed that the use of the sports boots significantly reduced flexion in the fetlock joint when compared to the non-treated limbs and the limbs to which the bandages had been applied. The hypothesis of this study was that there would be a significant difference in peak flexion angle of the knee at the trot between horses wearing bandage, again while wearing boots and again with bare limbs. Materials and methods Horses Kinematic data was collected from six horses ridden by six riders in this study. The horses had a mean weight of 565.1 + 57.3 kg, an age of 10.0 + 3.2 years. The horses had no signs of lameness when observed while trotting on a level concrete surface in a straight line. All the horses were accustomed to being ridden in the outdoor arena where the data were recorded. The data were recorded during ridden locomotion and all the horses were ridden by riders they were familiar with. Experimental design Each horse was trotted on a concrete surface to determine that it was not lame. After a warm up period of seven minutes walk and a seven minute trot horses were split into three groups with two horses in each group (X, Y, Z), the horses were assigned a number corresponding to a particular pattern of procedures distributed in a latin square arrangement shown in table 1 below. The three pairs of horses received three treatments (bandages, boots, bare limbs) over three phases.
The SMB II® and the Twenty X™ Polo Wrap were selected for this study.
The horses were trotted in a straight line in a path in front of and perpendicular to the view of a video recorder. One taped sequence (for left body side views) per phase for each of the three treatment groups were recorded of each horse while trotting for data analysis.
Stride cycle events were predefined prior to the study. One stride was determined to occur from toe down to toe down in the same limb. Toe down occurred at the frame in the video where initial contact occurred between the hoof and the asphalt surface. Toe off was defined as first frame in the video in which the hoof
left contact with the bearing surface.
Equipment Circular reflective markers were placed at the following anatomical landmarks to make the calculation of knee joint angle easier: the lateral aspect of the elbow, carpal, and metacarpophalangeal joints, and the lateral aspect of each hoof of the left and right forelimbs. The motion of the horse was recorded using a Samsung (SMX-F30) portable video camera. Uncompressed audio video interleave (avi) files produced from this camera were analyzed using a kinematic motion analysis system (ONTRACK EQUINE®).
The significance level was set at p<0.05. Data for all six horses was processed using SPSS 17.0 statistical software. The null hypothesis stated that there was no difference in peak flexion angle of the knee between horses wearing bandages, boots and with bare limbs. The data for peak flexion angle of the knee was interval. Variables were tested for normality of distribution using the Kolmogorov - Smirnov statistical test
(see Table 1; Appendix 1). The data was normally distributed. One-way repeated measures ANOVA analyses of variance
(see Table 1; Appendix 2) was performed
in SPSS 17.0 statistical software for the knee joint angles using the six subjects to look for biomechanical differences of the three treatments. The kinematic parameter for this study was peak flexion angle of the knee.
Results There was no significant difference in peak flexion angle of the knee between horses wearing bandages, boots and bare limbs (Table 2). Mean (±s.e) peak flexion angle of the knee for bandages was 126° (±0.81), 129.2° (±1.70) for boots and 127.8° (±1.23) for bare limbs.
1 one-way repeated measures ANOVA
Discussion The objective of this experiment was to test the hypothesis that there would be a significant difference in peak flexion of the carpal joint at the trot between horses wearing boots, bandages and with bare limbs. Statistical analysis of the horses' peak flexion angle of the knee at the trot through the use of the one-way repeated measures ANOVA indicated that there was no significant difference in peak flexion angle of the knee between the three treatments. There could possibly be a difference between the bandages and boots, however this study did not assess that hypothesis. There could be two possible explanations for these results. The first and most obvious one is that the knee was not physically restricted by any of the three treatments during the exercise. This is supported by Ramon et al. (2004) who found that athletic taping had a significant difference on peak flexion of the fetlock joint during the swing phase but no significant difference in any other joints. This seems logical since the taping wraps around the fetlock and thereby imposing some restriction on it which is not the case for other joints. The second explanation could be that the knee does not experience much strain during the swing phase because it is non-weight bearing during this time. The results could have been different if we had measured the peak extension angle of the knee joint. This is because most of the stress during the stance phase is put on the flexor tendon and suspensory ligaments as the horses' feet hit the ground (Roman et al. 2004). Suspensory ligaments play a major role in helping avoid carpal injury by
absorbing axial forces transferred to it through joint surfaces (Bramlage et al. 1988) and stresses to the suspensory ligament and flexor tendons have been shown by Alexander et al. (2001) to cause significant alterations in carpal joint angles. Kicker et al. 2004 found that support boots and protective boots significantly reduced maximum extension of the fetlock and contradicted by Sanders (2009) who found that boots and bandages did not cause a significant reduction in peak fetlock extension, although these results appear to be conflicting, the results of the former were obtained through horses trotting on a treadmill as opposed to horses trotted on an asphalt surface in the latter. Buchner et al. (1994) found a significant difference between kinematic results gained on a treadmill and those which were collected overground for horses and Pereira et al. (2006) found that the same was true for rats; therefore the results cannot be quantitatively compared to each other. Since the flexor tendons are loaded during the stance phase (Meershoek et al. 2001) it would seem logical that reducing the tension on them would result in reducing the load on tendons and ligaments going up the knee and thereby reducing maximum extension angle of the knee. To confirm this, however, a separate trial would need to take place in order to assess the effect of both bandages and boots on maximum extension angle of the carpus compared to the non-treated limb (control) instead of the difference between three treatments. This would give us more meaningful data in terms of how bandages and boot affect the kinematics of horses. Certain limitations were associated with the study reported here which made the experiment less than ideal. In kinematic analysis, one of the major sources of biological error is due to the movement of skin-based markers in relation to the underlying bones (Clayton et al. 2004), which gives rise to errors during marker placement and during or between the measurements (Weller et al. 2006). Van Weeran et al (1990) found translational errors ranging from eight mm to 142 mm and that more displacement occurred in the proximal limb than the distal limb and van Weeran et al. (1992) had similar results. This is well recognized and documented (van Weeran et al. 1990; Bogert et al. 1990; Lucchetti et al. 1998; Barrey, 1999; Benoit et al. 2006; Miro et al. 2009; Bourne et al. 2009) limitation in kinematic analysis and there have been many studies both human (Fuller et al. 1997; Taylor et al. 2005) and equine (van Weeran et al. 1992) aiming to develop new methods to increase the accuracy of readings by trying to account for and correct errors caused by skin displacement. These methods are invasive and often involve the use of light emitting diodes and pins which are inserted directly into the bone which makes them impractical as the subjects often undergo surgery as well as experiencing a certain amount of pain. The accuracy of these methods is also questionable and we are not aware of any studies set up to assess how accurate these methods really are. It is generally believed however, that errors are so small for the distal limb they can be neglected (Clayton and Schamhardt, 2001). Although this is contradicted by Bogert et al. (1990) who found that without the use of correction methods errors of up to 15° in the knee angle can occur, the results this study are unreliable and irrelevant as it only included one pony that was analyzed at the walk. The type of video cameras used in kinematic analysis is another very important factor to take into consideration. According to (Clayton and Schamhardt, 2001) cameras with sampling rate of 60 Hz are suitable for kinematic analysis of horses at walking speed but a faster camera would be needed for analysis of gaits faster than a walk. The
camera used in this study had a resolution of (720 x 480) which equates to a sampling rate of 60 (Hz). Due to the inadequate speed of the camera and the higher speed of the trotting horses some frames were skipped and that caused the image to be distorted. The simplest solution to this problem is the use of more specialized high speed cameras which are widely available at sampling rates between 120 (Hz) up to 1000 (Hz). Another limitation associated with this study and one which seems to be widespread in most studies done using horses was the sample size (n=6). A small sample size cannot be representative of the population as a whole. This could also be one of the main reasons behind the great deal of contradiction between kinematic analysis studies. The horses in this study were trotted by six riders at different riding levels. This could have influenced the results due to the instructions given by the riders causing changes in the motion of the horses. Peham et al. (2001) compared the influence of a professional rider and a recreational rider on the kinematics of horses at the trot and found that the motion pattern consistency of horses ridden by a professional rider was more consistent than the recreational rider.
If the same rider had been used for all horses then the motion of the horses would be consistent.
Conclusion Ultimately, the experiment is a groundwork study, providing basic data that could be easily expanded in a less limited testing environment