OCLC: 1102269287
PROQUEST: 1871694439
The most common injuries in show jumping horses involve structures that provide support to, and limit extension of, the fetlock (metacarpophalangeal/metatarsophalangeal) joint during limb loading. High degrees of fetlock extension cause high strains in the supporting structures (suspensory ligament, and superficial and deep digital flexor tendons) and under repetitive loading conditions could cause injury to these structures. Thus, minimizing fetlock hyperextension during jumping could potentially decrease injuries to the fetlock.
Injury to fetlock structures is affected by several factors associated with limb loading and transfer of loads from the ground to the fetlock. These factors include fetlock extension angle, the timing of peak fetlock extension angle, interphalangeal joint motions, and hoof translations. Each of these factors is affected by surface mechanical properties such as vertical stiffness, peak impact load and horizontal cohesion. Further, the magnitude of fetlock extension is related to the magnitude of loads propagated up the limb from the ground, and arena surface materials are known to influence the external loads that horses experience during racing and jumping activities.
Limb kinematics and hoof translations have been compared between different types of surface materials. It is known that peak fetlock extension and the timing of peak fetlock extension differ in racehorses galloping on race surfaces made of different materials (e.g. dirt, synthetic). Greater peak fetlock extension would cause higher strains in fetlock supporting structures, and earlier timing of peak fetlock extension means that the loading rate in supporting structures is likely greater. Hoof translation in the surface has been observed to vary with race surfaces made of different materials, with lesser translations in surfaces composed of synthetic materials compared to dirt surfaces. The angle of the hoof when the hoof strikes the surface also differs between surfaces of different material composition and may affect the magnitude and timing of peak fetlock angle. Hoof angle at heel strike is expected to be flatter on stiffer surfaces and more toe-up on less stiff surfaces. Furthermore, it is likely that fetlock motion is affected by interphalangeal and carpal/tarsal motions because some fetlock supporting structures also cross the interphalangeal and carpal/tarsal joints. However, there is likely variation in mechanical properties within types of surface materials (e.g. dirt, synthetic) due to different components (e.g. sand, fiber, plastic, rubber), additives (e.g., water, wax, polymer) and management (e.g., harrowing, ripping).
Surface mechanical properties measured using mechanical instruments have been compared between surfaces composed of different materials. These surface mechanical properties are not just affected by material composition but also surface properties such as surface temperature, moisture content, and cushion depth. The peak force and stiffness measured during vertical impact of a track testing device (TTD) are known to differ among race surface materials. The cohesion of a surface differs between surfaces composed of different materials when tested horizontally using a shear test. However, there has not been an integrated study in which vertical and horizontal mechanical properties of surface materials have been directly related to fetlock, interphalangeal, or carpal/tarsal joint angles, or to hoof kinematics and translations.
The objectives of the current study were to 1) compare forelimb and hindlimb joint angles and hoof translations during take-off for a jump between surfaces of different materials, 2) compare vertical and horizontal mechanical properties measured by instruments between surfaces of different materials, and 3) relate the kinematic measurements from horses with measured mechanical properties of the surfaces. It is hypothesized that:
To test these hypotheses, the motions of 8 show jumping horses were recorded (Photron, 500Hz) during take-off for a jump over a standardized 1.1m oxer on 3 mechanically different surfaces; a dirt surface (Dirt), and a synthetic surface that was watered and harrowed in 2 different ways (Synthetic1, Synthetic2). Kinematic markers were placed on the left lateral side of each horse, for both fore and hind limbs. Surface stiffness and peak impact load in the vertical direction were characterized using the TTD. Cohesion of the surface materials in the horizontal direction was characterized using a shear test device. The effects of surface (Dirt, Synthetic1, Synthetic2) on kinematic variables were analyzed using an unbalanced mixed model analysis of covariance, with lead (Leading, Trailing for forelimb; Leading, Trailing, Both for hindlimb) as a fixed effect, and horse as a random effect. Relationships of peak fetlock extension and hoof translations with surface stiffness, peak impact load, and cohesion were examined using scatter plots.
The stiffest surface was the Dirt (8700 ± 520 kN/m, least square mean ± standard error), followed by Synthetic1 (5910 ± 690 kN/m) and Synthetic2 (3190 ± 620 kN/m). Peak impact loads were highest on Dirt (19656 ± 578 N, least square mean ± standard error), followed by Synthetic1 (15533 ± 771 N) and Synthetic2 (12509 ± 697 N). Synthetic1 had the highest surface cohesion, followed by Synthetic2 and then Dirt (cohesions of 8299, 5294, and 1288 N/m², respectively).
A significant surface effect was observed for maximum forelimb fetlock angle during takeoff (p < 0.001). Maximum forelimb fetlock angle was smallest for the Dirt surface (247.5 ± 4.5 degrees, least square mean ± standard error), larger for the Synthetic2 surface (250.0 ± 4.5 degrees), and largest on the Synthetic1 surface (257.0 ± 4.8 degrees). The difference between maximum forelimb fetlock angles during stance among surfaces ranged from 2.5 degrees to 9.5 degrees, which is likely to affect clinically relevant distal limb tendon strains. Statistically significant surface effects were not observed for the timing of maximum forelimb fetlock angle among surfaces (p > 0.05).
Surface did not have a significant effect on maximum hindlimb fetlock angle (p > 0.05), but it did have a significant effect on the timing of maximum hindlimb fetlock angle (p = 0.006). Maximum hindlimb fetlock angle occurred earlier during stance on the Synthetic1 surface (55.6 ± 3.7% of stance) than on the Dirt (69.3 ± 2.4%) and Synthetic2 surfaces (69.8 ± 2.4% of stance).
A significant surface effect was observed for hoof translation during take-off for a jump. Forelimb hoof heel translation in the cranial (forward) direction during support was greatest (p=0.033) on the Synthetic1 surface (0.69 ± 0.43 cm), followed by the Dirt surface (-0.19 ± 0.31 cm) and Synthetic2 surface (-0.52 ± 0.32 cm). Hindlimb hoof heel translation in the cranial direction was greatest (p=0.008) on the Dirt surface (0.00 ± 0.15 cm), followed by the Synthetic1 surface (-0.32 ± 0.23 cm), and the Synthetic2 surface (-0.68 ± 0.16 cm).
Forelimb hoof angle at heel-strike was significantly different (p = 0.037) among surfaces. Hoof angle was most toe-up on the Synthetic1 surface (-21.3 ± 3.1 degrees), followed by the Dirt (-13.2 ± 2.2 degrees) and Synthetic2 (-13.1 ± 2.2 degrees) surfaces. Hindlimb hoof angle at heelstrike was also significantly different (p = 0.004) among surfaces. Hindlimb hoof angle was most toe-up on the Synthetic1 surface (-8.3 ± 3.5 degrees), followed by the Synthetic2 surface (- 4.6 ± 2.8 degrees) and the Dirt surface (0.3 ± 2.6 degrees).
A significant surface effect was observed for forelimb maximum carpal angle during takeoff (p = 0.0020). Maximum carpal angle was smallest for the Synthetic1 surface (181.0 ± 2.1 degrees, least square mean ± standard error), larger for the Dirt surface (184.3 ± 2.0 degrees), and largest on the Synthetic2 surface (185.1 ± 2.0 degrees). A significant surface effect was observed for the timing of maximum forelimb carpal angle (p = 0.0191), which occurred earliest during on the Synthetic1 surface (32.2 ± 3.5 % of stance), followed by Dirt (32.8 ± 2.3 % of stance), and latest on Synthetic2 (41.3 ± 2.3 % of stance).
A significant surface effect was observed for hindlimb maximum tarsal angle during takeoff (p = 0.0396). Maximum tarsal angle was smallest for the Dirt surface (246.3 ± 2.6 degrees, least square mean ± standard error), larger for the Synthetic2 surface (246.9 ± 2.7 degrees), and largest on the Synthetic1 surface (253.4 ± 3.3 degrees). A significant surface effect was observed for the timing of maximum hindlimb tarsal angle (p = 0.0204), which occurred earliest during on the Synthetic2 surface (43.2 ± 1.1 % of stance), followed by Synthetic1 (43.9 ± 1.5 % of stance), and latest on Dirt (45.6 ± 1.1 % of stance).
Surface had a significant effect on forelimb maximum interphalangeal angle during takeoff (p = 0.0009), but it did not have a significant effect on the timing of forelimb maximum interphalangeal angle (p > 0.05). Maximum forelimb interphalangeal angle was smallest for the Dirt surface (172.1 ± 3.2 degrees, least square mean ± standard error), larger for the Synthetic2 surface (172.2 ± 3.2 degrees), and largest on the Synthetic1 surface (184.0 ± 3.9 degrees).
Surface had a significant effect on hindlimb maximum interphalangeal angle during takeoff (p = 0.0060), but it did not have a significant effect on the timing of hindlimb maximum interphalangeal angle (p > 0.05). Maximum hindlimb interphalangeal angle was smallest for the Synthetic2 surface (179.7 ± 5.0 degrees, least square mean ± standard error), larger for the Dirt surface (183.0 ± 5.0 degrees), and largest on the Synthetic1 surface (191.0 ± 5.4 degrees).
Linear relationships were not observed between peak fetlock angle and surface stiffness or peak load. Maximum fetlock angle (forelimb and hindlimb) more closely paralleled cohesion than stiffness or peak impact load. Linear relationships were also not observed between hoof translations and surface cohesion. Hoof angle at heel-strike more closely paralleled shear data.
In summary, some limb and hoof kinematic quantities varied with track surface, but not as expected. One objective of the study was to determine a relation between maximum fetlock extension and the stiffness or peak impact load of different surfaces. However, no clear relationship was identified and we suspect that maximum fetlock extension depends on more than one surface mechanical property. While maximum fetlock angle was found to be different between surfaces, it appeared that the angle was more closely associated with cohesion than stiffness or peak impact load. Further work needs to be done with greater numbers of horses and surfaces to elucidate the relationships between surface properties and limb motions. Because the mechanical properties of a surface can be controlled by surface composition and maintenance, the understanding of how limb kinematics differ over different surfaces with different known mechanical properties could help arena managers and owners to make informed decisions in arena design and management to reduce the risk of musculoskeletal injuries in show jumping horses.