Dynamic properties of a dirt and a synthetic equine racetrack surface measured by a track-testing device

Arena surface vertical impact forces vary with surface compaction

Mechanical properties of arena surfaces are extrinsic factors for musculoskeletal injury. Vertical impact forces of harrowed and compacted cushion were measured at five locations on 12 arena surfaces (five dirt, seven synthetic [dirt and fiber]). Eight variables related to impact force, displacement, and acceleration were calculated. Surface temperature, cushion depth and moisture content were also measured. The effects of surface material type (dirt/synthetic) and cushion compaction (harrowed/compacted) on vertical impact properties were assessed using an analysis of variance. Relationships of manageable surface properties with vertical impact forces were examined through correlations. Compacted cushion exhibited markedly higher vertical impact force and deceleration with lower vertical displacement than harrowed cushion (P < 0.001), and the effect was greater on dirt than synthetic surfaces (P = 0.039). Vertical displacement (P = 0.021) and soil rebound (P = 0.005) were the only variables affected by surface type. Surface compaction (harrowed, compacted) had a significantly greater effect on vertical impact forces than surface type (dirt, synthetic). By reducing surface compaction through harrowing, extrinsic factors related to musculoskeletal injury risk are reduced. These benefits were more pronounced on dirt than synthetic surfaces. These results indicate that arena owners should regularly harrow surfaces, particularly dirt surfaces.

Shear ground reaction force variation among equine arena surfaces

Shear forces at the surface-hoof interface affect hoof slide, surface grip, forces transferred to the limb, and injury risk. However, the variation in shear forces among surfaces with different compositions have not been quantified. Shear ground reaction forces were measured on five dirt and seven synthetic arena surfaces. Cohesion/adhesion and angle of internal friction/coefficient of friction were calculated. Surface composition, surface temperature, cushion depth, and moisture content were also measured. The effects of surface material (dirt/synthetic) on shear properties were assessed using analysis of variance (ANOVA; P < 0.05). The relationships between surface composition or management properties and shear properties were analyzed using linear correlation. Shear properties were not different between dirt and synthetic surface categories; however, surface fiber content was correlated with adhesion and coefficient of friction. These correlations predict that more fiber will decrease soil adhesion (r = -0.75; P < 0.01) and increase the coefficient of friction (r = 0.81; P < 0.01). Furthermore, maximum shear force was significantly correlated with cushion depth (r = 0.61; P < 0.01) and moisture content (r = 0.57; P < 0.01), where shear force was greater on surfaces with thicker cushion layers or higher moisture content. The findings suggest that shear mechanical behavior is more dependent on surface composition than surface material categories (dirt/synthetic) and also indicate that arena owners can influence shear forces by adjusting either surface composition or management.

Hoof Impact and Foot-Off Accelerations in Galloping Thoroughbred Racehorses Trialling Eight Shoe-Surface Combinations

The athletic performance and safety of racehorses is influenced by hoof−surface interactions. This intervention study assessed the effect of eight horseshoe−surface combinations on hoof acceleration patterns at impact and foot-off in 13 galloping Thoroughbred racehorses retired from racing. Aluminium, barefoot, GluShu (aluminium−rubber composite) and steel shoeing conditions were trialled on turf and artificial (Martin Collins Activ-Track) surfaces. Shod conditions were applied across all four hooves. Tri-axial accelerometers (SlamStickX, range ±500 g, sampling rate 5000 Hz) were attached to the dorsal hoof wall (x: medio-lateral, medial = positive; y: along dorsal hoof wall, proximal = positive; and z: perpendicular to hoof wall, dorsal = positive). Linear mixed models assessed whether surface, shoeing condition or stride time influenced maximum (most positive) or minimum (most negative) accelerations in x, y and z directions, using ≥40,691 strides (significance at p < 0.05). Day and horse−rider pair were included as random factors, and stride time was included as a covariate. Collective mean accelerations across x, y and z axes were 22−98 g at impact and 17−89 g at foot-off. The mean stride time was 0.48 ± 0.07 s (mean ±2 SD). Impact accelerations were larger on turf in all directions for forelimbs and hindlimbs (p ≤ 0.015), with the exception of the forelimb z-minimum, and in absolute terms, maximum values were typically double the minimum values. The surface type affected all foot-off accelerations (p ≤ 0.022), with the exception of the hindlimb x-maximum; for example, there was an average increase of 17% in z-maximum across limbs on the artificial track. The shoeing condition influenced all impact and foot-off accelerations in the forelimb and hindlimb datasets (p ≤ 0.024), with the exception of the hindlimb impact y-maximum. Barefoot hooves generally experienced the lowest accelerations. The stride time affected all impact and foot-off accelerations (p < 0.001). Identifying factors influencing hoof vibrations upon landing and hoof motion during propulsion bears implication for injury risk and racing outcomes.

A Coupled Biomechanical-Smoothed Particle Hydrodynamics Model for Horse Racing Tracks

Distal limb injuries are common in racing horses and track surface properties have been associated with injury risk. To better understand how track surfaces may contribute to equine limb injury, we developed the first 3D computational model of the equine hoof interacting with a racetrack and simulated interactions with model representations of 1) a dirt surface and 2) an all-weather synthetic track. First, a computational track model using the Smoothed Particle Hydrodynamics (SPH) method with a Drucker-Prager (D-P) elastoplastic material model was developed. It was validated against analytical models and published data and then calibrated using results of a custom track testing device applied to the two racetrack types. Second, a sensitivity analysis was performed to determine which model parameters contribute most significantly to the mechanical response of the track under impact-type loading. Third, the SPH track model was coupled to a biomechanical model of the horse forelimb and applied to hoof-track impact for a horse galloping on each track surface. We found that 1) the SPH track model was well validated and it could be calibrated to accurately represent impact loading of racetrack surfaces at two angles of impact; 2) the amount of harrowing applied to the track had the largest effect on impact loading, followed by elastic modulus and cohesion; 3) the model is able to accurately simulate hoof-ground interaction and enables study of the relationship between track surface parameters and the loading on horses’ distal forelimbs.

Response of the Thoroughbred forelimb to perturbations caused by a change in ground surface

Thoroughbred racehorses are often affected by musculoskeletal injuries, leading to involuntary rest, early retirement or death. Hardness and consistency of the track surface have been implicated as major risk factors for limb injury. The purpose was to test the utility of a preliminary AnyBody musculoskeletal model of the equine forelimb for its responses on two perturbing surfaces. A musculoskeletal model was developed using CT, muscle, tendon and ligament properties, and kinematic data were applied from ridden trials using five Thoroughbred horses. Horses were ridden at trot and canter on a baseline sand surface, and through two perturbation pits containing a harder and a softer surface for one stance phase. In response to the hard perturbation, the proximal limb was more compliant at trot and canter, as measured by increased shoulder flexion in the perturbed stance phase and increased elbow and carpal flexion in the subsequent swing phase. The suspensory ligaments and muscle-tendon units were less strained while lacertus fibrosus was more strained. In response to the soft perturbation, the coffin joint was more flexed and the elbow was more extended in the acute stance phase at trot, resulting in increased strain to the DDF, extensor branches and lacertus fibrosus. At canter, the coffin was more flexed, the fetlock less hyperextended and so the suspensory structures were less strained in the perturbed stance phase, but more strained in the second stance phase. Changes in ground surface affect both the perturbed stance phase, and the following stance phase.

The effect of horseshoes and surfaces on horse and jockey centre of mass displacements at gallop

Horseshoes influence how horses' hooves interact with different ground surfaces, during the impact, loading and push-off phases of a stride cycle. Consequently, they impact on the biomechanics of horses' proximal limb segments and upper body. By implication, different shoe and surface combinations could drive changes in the magnitude and stability of movement patterns in horse-jockey dyads. This study aimed to quantify centre of mass (COM) displacements in horse-jockey dyads galloping on turf and artificial tracks in four shoeing conditions: 1) aluminium; 2) barefoot; 3) GluShu; and 4) steel. Thirteen retired racehorses and two jockeys at the British Racing School were recruited for this intervention study. Tri-axial acceleration data were collected close to the COM for the horse (girth) and jockey (kidney-belt), using iPhones (Apple Inc.) equipped with an iOS app (SensorLog, sample rate = 50 Hz). Shoe-surface combinations were tested in a randomized order and horse-jockey pairings remained constant. Tri-axial acceleration data from gallop runs were filtered using bandpass Butterworth filters with cut-off frequencies of 15 Hz and 1 Hz, then integrated for displacement using Matlab. Peak displacement was assessed in both directions (positive 'maxima', negative 'minima') along the cranio-caudal (CC, positive = forwards), medio-lateral (ML, positive = right) and dorso-ventral (DV, positive = up) axes for all strides with frequency ≥2 Hz (mean = 2.06 Hz). Linear mixed-models determined whether surfaces, shoes or shoe-surface interactions (fixed factors) significantly affected the displacement patterns observed, with day, run and horse-jockey pairs included as random factors; significance was set at p<0.05. Data indicated that surface-type significantly affected peak COM displacements in all directions for the horse (p<0.0005) and for all directions (p≤0.008) but forwards in the jockey. The largest differences were observed in the DV-axis, with an additional 5.7 mm and 2.5 mm of downwards displacement for the horse and jockey, respectively, on the artificial surface. Shoeing condition significantly affected all displacement parameters except ML-axis minima for the horse (p≤0.007), and all displacement parameters for the jockey (p<0.0005). Absolute differences were again largest vertically, with notable similarities amongst displacements from barefoot and aluminium trials compared to GluShu and steel. Shoe-surface interactions affected all but CC-axis minima for the jockey (p≤0.002), but only the ML-axis minima and maxima and DV-axis maxima for the horse (p≤0.008). The results support the idea that hoof-surface interface interventions can significantly affect horse and jockey upper-body displacements. Greater sink of hooves on impact, combined with increased push-off during the propulsive phase, could explain the higher vertical displacements on the artificial track. Variations in distal limb mass associated with shoe-type may drive compensatory COM displacements to minimize the energetic cost of movement. The artificial surface and steel shoes provoked the least CC-axis movement of the jockey, so may promote greatest stability. However, differences between horse and jockey mean displacements indicated DV-axis and CC-axis offsets with compensatory increases and decreases, suggesting the dyad might operate within displacement limits to maintain stability. Further work is needed to relate COM displacements to hoof kinematics and to determine whether there is an optimum configuration of COM displacement to optimise performance and minimise injury.

Influence of Speed, Ground Surface and Shoeing Condition on Hoof Breakover Duration in Galloping Thoroughbred Racehorses

Simple Summary

In the stride cycle of a horse, there is a period of time when the hoof pushes off from the ground surface and rotates through an angle of approximately 90 degrees before it is lifted off. This time period is known as hoof breakover. Using slow-motion video footage, this study measured breakover duration in retired Thoroughbred racehorses galloping at a range of speeds on two surfaces (artificial and turf) in four shoeing conditions (aluminium, barefoot, GluShu and steel). Hooves from different limbs were assessed separately in this asymmetric gait. Increasing speed was correlated with decreasing breakover duration, and this trend was more enhanced in the hindlimbs than in the forelimbs at high gallop speeds. Breakover duration was faster on the artificial surface compared to the turf surface for all limbs, under the ground conditions studied. The first limb to contact the ground surface after the suspension phase (the ‘non-leading’ hindlimb), was additionally influenced by shoeing condition and an interaction that occurred between shoeing condition and speed. Determining parameters that alter breakover duration will be important for lowering the risk of musculo-skeletal injuries, optimising gait quality and improving performance in galloping racehorses during both training and racing.

Abstract

Understanding the effect of horseshoe–surface combinations on hoof kinematics at gallop is relevant for optimising performance and minimising injury in racehorse–jockey dyads. This intervention study assessed hoof breakover duration in Thoroughbred ex-racehorses from the British Racing School galloping on turf and artificial tracks in four shoeing conditions: aluminium, barefoot, aluminium–rubber composite (GluShu) and steel. Shoe–surface combinations were tested in a randomized order and horse–jockey pairings (n = 14) remained constant. High-speed video cameras (Sony DSC-RX100M5) filmed the hoof-ground interactions at 1000 frames per second. The time taken for a hoof marker wand fixed to the lateral hoof wall to rotate through an angle of 90 degrees during 384 breakover events was quantified using Tracker software. Data were collected for leading and non-leading forelimbs and hindlimbs, at gallop speeds ranging from 23–56 km h⁻¹. Linear mixed-models assessed whether speed, surface, shoeing condition and any interaction between these parameters (fixed factors) significantly affected breakover duration. Day and horse–jockey pair were included as random factors and speed was included as a covariate. The significance threshold was set at p < 0.05. For all limbs, breakover times decreased as gallop speed increased (p < 0.0005), although a greater relative reduction in breakover duration for hindlimbs was apparent beyond approximately 45 km h⁻¹. Breakover duration was longer on turf compared to the artificial surface (p ≤ 0.04). In the non-leading hindlimb only, breakover duration was affected by shoeing condition (p = 0.025) and an interaction between shoeing condition and speed (p = 0.023). This work demonstrates that speed, ground surface and shoeing condition are important factors influencing the galloping gait of the Thoroughbred racehorse.

Development of An Anybody Musculoskeletal Model of The Thoroughbred Forelimb

Musculoskeletal injuries in horses are the main cause of retirement, rest, and death. To understand these injuries, it is necessary to study loads in muscles, tendons and ligaments. A musculoskeletal model makes it possible to consider all structures simultaneously and avoids invasive measurements. At present, most computational models of the equine limb described in the literature have been limited to the distal limb. The aim of this study was to create a preliminary musculoskeletal model of the whole equine forelimb and to run it with kinematic data collected during gait. The model was developed with the AnyBody Modelling System. It includes six limb segments, 11 muscle groups and 17 ligaments. Kinematic data were collected from the right forelimb of four Thoroughbreds at trot, right and left lead canter, and were then used in the model to compute sagittal plane joint excursions and ligament and tendon strains. The modelled joint excursions were in reasonable agreement with previous reports in the literature despite breed, gait and surface differences. Strain patterns of the tendons of the suspensory apparatus agreed with the literature, with maxima in mid-stance or at the end of stance. Strains in the distal palmar ligaments peaked in mid-stance, while strain in lacertus fibrosus peaked at the stance-swing transition. Tendon and ligament strains at canter were greatest when the measured forelimb was the trailing limb. Strain amplitudes varied against earlier models and these differences are discussed in relation to variations in methods, and especially in relation to attachment points of tendons and ligaments.

Appraising the Welfare of Thoroughbred Racehorses in Training in Queensland, Australia: The Incidence and Type of Musculoskeletal Injuries Vary between Two-Year-Old and Older Thoroughbred Racehorses

Simple Summary

Musculoskeletal injuries (MSI) remain a concerning cause of racehorse morbidity and mortality with serious ethical and welfare consequences. Previous research examining risk factors for injuries report inconsistent findings. Age is thought to affect the risk of injury, but, to date, there have been no prospective studies specifically comparing injuries between two-year-old versus older horses. We aimed to: (1) determine the incidence of injuries for two-year-old and older horses, and whether this was affected by training track, season, or rainfall, and (2) determine the types of injuries affecting two-year-old and older horses, and whether horses trialled or raced after injury. Data were collected through personal structured weekly interviews with participating trainers over a 13-month period. Data were analysed using Poisson regression. The incidence of MSI in the current study was low (0.6%). The incidence of MSI in two-year-old horses was higher than older horses. Types of MSI varied between two-year-old and older horses and affected whether horses subsequently trialled or raced from 11 to 23 months after injury. A larger proportion of two-year-old horses had dorsal metacarpal disease and traumatic lacerations. A smaller proportion of two-year-old horses had suspensory desmitis, superficial digital flexor tendonitis, proximal sesamoid bone fractures, and fetlock joint injuries than older horses. Training track and rainfall did not affect the incidence of injuries. The season affected the incidence of injuries in two-year-old horses but not in older horses.

Abstract

Musculoskeletal injuries (MSI) remain a concerning cause of racehorse morbidity and mortality with important ethical and welfare consequences. Previous research examining risk factors for MSI report inconsistent findings. Age is thought to affect MSI risk, but, to date, there have been no prospective studies comparing MSI in two-year-old versus older horses. This study aimed to: (1) determine the incidence of MSI for two-year-old and older horses, and whether this was affected by training track, season, or rainfall, and (2) determine the types of MSI affecting two-year-old and older horses, and whether horses trialled or raced after injury. A prospective survey was conducted with data collected through personal structured weekly interviews with participating trainers over a 13-month period. Data were analysed using Poisson regression. The incidence of MSI in the current study was low (0.6%). The incidence of MSI in two-year-old horses was higher than older horses (p < 0.001). Types of MSI varied between two-year-old and older horses (p < 0.001) and affected whether horses subsequently trailed or raced from 11 to 23 months after injury (p < 0.001). A larger proportion of two-year-old horses had dorsal metacarpal disease and traumatic lacerations. A smaller proportion of two-year-old horses had suspensory ligament desmitis, superficial digital flexor tendonitis, proximal sesamoid bone fractures, and fetlock joint injuries than older horses. Training track and rainfall did not affect MSI. The season affected MSI in two-year-old horses (p < 0.001) but not older horses. The major limitation was that trainers in this study were metropolitan (city) and our findings may not be generalisable to racehorses in regional (country) areas. Another significant limitation was the assumption that MSI was the reason for failure to trial or race after injury. In conclusion, the incidence of MSI was low in the current study and the types and the risk factors for MSI are different for two-year-old and older horses.

A Cross-Sectional Survey of the Training and Management of a Cohort of 2-Year-Old Standardbred Racehorses in New Zealand

There are limited data on the training and management practices of Standardbred trainers in New Zealand. The aims of this study were to describe the 2-year-old training practices of Standardbred trainers and to examine if there were differences in the production process between public (commercial) and amateur (licensed-to-train) trainers. An online Qualtrics survey was conducted after the 2016/7 racing season and completed by 154 Standardbred trainers, 88 (57%) of which had 2-year-olds in training. Descriptive statistics were used to describe the data stratified by public and licensed-to-train trainers. Most of the 2-year-old horses in work were homebred (bred by the trainer), with public trainers more likely to break in their horses themselves (85% vs. 64%, P = .04). The training pattern of 2-year-olds was similar for public trainers and licensed-to-train trainers, and was influenced by either convenience or the physical maturity of individual horses. Most trainers were reluctant to retire any 2-year-old. The prevalence of involuntary breaks for 2-year-olds was low (9.1%, 95% CI 6.6%-12.4%). Most trainers used 800 m (½ mile) oval, crusher dust ("all-weather") or sand tracks, with most public trainers using tracks with banked corners (88% vs. 59%, P < .01) and recording the times of horse workouts (79% vs. 45%, P < .01). The cross-section of trainers surveyed reflected the nature of the Standardbred industry in New Zealand with a high bias toward amateur owner/breeder/trainers, with few horses in work than public trainers who had a more commercial focus.

Track Surfaces Used for Ridden Workouts and Alternatives to Ridden Exercise for Thoroughbred Horses in Race Training

Little is known about the types of surfaces used during training of Thoroughbred racehorses or methods of exercise used in addition to ridden track-work. Our aims were to (1) describe the types of surfaces used in the training of Thoroughbred racehorses and to (2) identify alternative approaches used to exercise horses in addition to, or in place of, ridden overground track-work. Information regarding surface and alternative exercise methods was collected as part of an in-person survey of training practices of 66 registered Thoroughbred trainers in Victoria, Australia. Sand and synthetic surfaces were used by 97% and 36% of trainers respectively for slow-workouts, with galloping on turf training tracks used in training regimens by 82% and synthetic by 58% of trainers. Of those trainers utilising turf tracks, only 34% of gallop training was completed on turf despite turf being the predominant racing surface. Almost 90% of trainers used alternatives to ridden exercise. There is substantial variation in training surface used and alternative types of exercise undertaken by Victorian trainers. Future research should focus on how such practices relate to injury risk, particularly as it relates to the importance of musculoskeletal adaptation to specific race-day surfaces.

Does 'hacking' surface type affect equine forelimb foot placement, movement symmetry or hoof impact deceleration during ridden walk and trot exercise?

BACKGROUND

Both pleasure and competition horses regularly exercise on surfaces such as tarmac, gravel and turf during 'hacking'. Despite this, there is limited evidence relating to the effect of these surfaces upon foot-surface interaction.

OBJECTIVES

To investigate forelimb foot placement, hoof vibration and movement symmetry in pleasure horses on three commonly encountered hacking surfaces.

STUDY DESIGN

Quantitative gait study in a convenience sample.

METHODS

Six horses regularly partaking in hacking exercise were ridden in walk and trot on all surfaces. Horses were equipped with one hoof-mounted, accelerometer and four body-mounted inertial measurement units (IMUs) to measure foot impact and movement symmetry. High-speed (400 FPS) video footage of foot-placement was acquired (dorsal, palmar, lateral views). Foot-impact and movement symmetry were analysed with a mixed effects model and Bowker symmetry tests for foot-placement analysis.

RESULTS

Vibration power and frequency parameters increase as perceived surface firmness increases from grass, to gravel, to tarmac (P≤0.001). Vibration power parameters were consistently greater at trot compared with walk (P≤0.001), but the same was not true for vibration frequency (P≥0.2). Greatest movement asymmetry was recorded during grass surface trotting. No significant difference in foot-placement was detected between the three surfaces.

MAIN LIMITATIONS

This was a field study using three commonly encountered hacking surfaces. Surface properties change easily with water content and temperature fluctuations so care must be taken when considering other similar surfaces, especially at different times of the year. Six leisure horses were used so the results may not be representative of horses of all types.

CONCLUSIONS

Vibration parameters generally increase as perceived surface firmness increases. Increasing speed alters vibration power but not frequency. Further investigations are required to determine the role that this may play in the development of musculoskeletal disease in horses.

Numerical time-domain modelling of hoof-ground interaction during the stance phase

BACKGROUND

Hoof-ground interaction impacts on the health and performance characteristics of horses. Due to complex interactions between hoof and ground during the stance phase, previous experimentally dominated studies concentrated on subproblems of the phenomena observed. A multidisciplinary methodology with mathematical modelling, material testing and in vivo experimental measurements seems promising.

OBJECTIVES

With the help of a mathematical approach, this contribution aims to explain from a biomechanical point of view the phenomena observed during experimental investigations (hoof acceleration, interacting forces) and aims to contribute to an overall experimental-mathematical multidisciplinary approach.

STUDY DESIGN

In silico modelling of hoof-ground interaction (limb, hoof and horizontally unbounded ground).

METHODS

Hoof-ground interaction is represented by a time-domain finite element model including the limb, the hoof and the unbounded representation of the ground via the scaled boundary finite element method to capture radiation damping during the stance phase. Motoric forces (driving forces) of the horse during locomotion are included.

RESULTS

Numerical model results for acceleration-time relations (hoof) at different trotting velocities are compared with previously published acceleration-time relations and show qualitative agreement. From the model approach, power loss due to different ground properties and ground damping is computed in combination with the maximum limb force during the stance phase.

MAIN LIMITATIONS

Intentionally, a simplified model approach for the material and structural representation of the limb, the hoof and the ground in terms of material features and spatial resolution has been used for this study, which might be the basis for a model refinement in terms of contact properties as well as the integration of bone and joint structures.

CONCLUSIONS

The comparison to experimentally obtained results demonstrates the applicability of the model, which, in turn, enables an insight into the processes taking place during hoof-ground interaction.

Modelling the effect of race surface and racehorse limb parameters on in silico fetlock motion and propensity for injury

BACKGROUND

The metacarpophalangeal joint (fetlock) is the most commonly affected site of racehorse injury, with multiple observed pathologies consistent with extreme fetlock dorsiflexion. Race surface mechanics affect musculoskeletal structure loading and injury risk because surface forces applied to the hoof affect limb motions. Race surface mechanics are a function of controllable factors. Thus, race surface design has the potential to reduce the incidence of musculoskeletal injury through modulation of limb motions. However, the relationship between race surface mechanics and racehorse limb motions is unknown.

OBJECTIVE

To determine the effect of changing race surface and racehorse limb model parameters on distal limb motions.

STUDY DESIGN

Sensitivity analysis of in silico fetlock motion to changes in race surface and racehorse limb parameters using a validated, integrated racehorse and race surface computational model.

METHODS

Fetlock motions were determined during gallop stance from simulations on virtual surfaces with differing average vertical stiffness, upper layer (e.g. cushion) depth and linear stiffness, horizontal friction, tendon and ligament mechanics, as well as fetlock position at heel strike.

RESULTS

Upper layer depth produced the greatest change in fetlock motion, with lesser depths yielding greater fetlock dorsiflexion. Lesser fetlock changes were observed for changes in lower layer (e.g. base or pad) mechanics (nonlinear), as well as palmar ligament and tendon stiffness. Horizontal friction and fetlock position contributed less than 1° change in fetlock motion.

MAIN LIMITATIONS

Simulated fetlock motions are specific to one horse's anatomy reflected in the computational model. Anatomical differences among horses may affect the magnitude of limb flexion, but will likely have similar limb motion responses to varied surface mechanics.

CONCLUSIONS

Race surface parameters affected by maintenance produced greater changes in fetlock motion than other parameters studied. Simulations can provide evidence to inform race surface design and management to reduce the incidence of injury.

Diagnostic approach to catastrophic musculoskeletal injuries in racehorses

Catastrophic musculoskeletal injuries are the most common cause of euthanasia or spontaneous death in racehorses, and the most common cause of jockey falls with potential for serious human injury. Horses are predisposed to the vast majority of these injuries by preexisting lesions that can be prevented by early diagnosis and adequate bone injury management. A thorough examination of the musculoskeletal system in racehorses often determines the cause of these injuries and generates data to develop injury prevention strategies. We describe the diagnostic approach to musculoskeletal injury, review the methodology for the examination of racehorse limbs, and provide anatomy and pathology tools to perform an organized and thorough postmortem examination of the musculoskeletal system in equine athletes.

Hitting the ground running: Evaluating an integrated racehorse limb and race surface computational model

Race surface mechanics contribute to musculoskeletal injury in racehorses. These mechanics affect ground reaction forces applied to the hoof, and thus limb motions during stance that can contribute to musculoskeletal pathologies. Race surface design has been largely empirical within the industry, with little uniform consensus for injury prevention and performance. Furthermore, race surface installations are too expensive to install experimentally. The objective of this research was to develop and evaluate an integrated racehorse limb and race surface computational model. Combined forward/inverse dynamic simulations of distal leading forelimb motions of a galloping horse during stance were compared to 2D distal leading forelimb kinematics of actual galloping racehorses on race surfaces with measured mechanics. Model predicted angular and translational kinematic profiles had similar qualitative shapes as experimental data, with comparable peak magnitudes. Model predictions of peak metacarpophalangeal position and timing were within 11° and 8ms of mean experimental data. The model overestimated peak fetlock angular velocity on consolidated surfaces (up to 1390°/s), and hoof displacements (up to 4cm) during stance. The model's ability to produce comparable qualitative kinematic profiles to experimental data and biologically reasonable fetlock and hoof motions support the future use of this model to explore the effect of race surface parameters on increasing or decreasing distal limb motions and provide supportive evidence for potential mechanisms of injury.

Descriptive statistics and the pattern of horse racing in New Zealand. 2. Harness racing

The aim of the present study was to describe the pattern of pacing and trotting races and starts, including temporal trends, in Harness racing in New Zealand. Data on all race starts between 1 August 2005 and 31 July 2010 were supplied by Harness Racing New Zealand. Descriptive statistics were used to describe the data at both race and starts level, stratified by pacing and trotting races. In total, 78% of races run were pacing races and most races occurred in the Southern region. The start type varied by race, with most pacing races run with mobile starts and trotting races with standing starts. Regardless of race type most races were run on all-weather tracks and were run in the summer or autumn. There was little change in the median number of starts per horse over time and the median number of starters per trainer per year was 16 (interquartile range 7–35, max. 612) and 12 (interquartile range 5–24, max. 235) for pacing and trotting races, respectively. Differences in track surfaces, gait, region and drivers between the Standardbred and the Thoroughbred industry suggests a need for data specific to the Harness racing industry in New Zealand. This study provided baseline data on the pattern of Standardbred racing and highlighted factors unique to the Harness racing industry in New Zealand.

Hoof position during limb loading affects dorsoproximal bone strains on the equine proximal phalanx

Sagittal fractures of the proximal phalanx (P1) in the racehorse appear to be associated with turf racing surfaces, which are known to restrict forward slide of the foot at impact. We hypothesized that restriction of forward foot slip would result in higher P1 bone strains during metacarpophalangeal joint (MCPJ) hyperextension. Unilateral limbs from six equine cadavers were instrumented with strain gauges and bone reference markers to measure dorsoproximal P1 bone strains and MCPJ extension, collateromotion and axial rotation during in vitro limb loading to 10,500 N. By limiting movement of the distal actuator platform, three different foot conditions (forward, free, and restricted) were applied in a randomised block design. Bone reference markers, recorded by video, were analyzed to determine motion of P1 relative to MC3. Rosette strain data were reduced to principal and shear magnitudes and directions. A mixed model ANOVA determined the effect of foot position on P1 bone strains and MCPJ angles. At 10,000 N load, the restricted condition resulted in higher P1 axial compressive (p=0.015), maximum shear (p=0.043) and engineering shear (p=0.046) strains compared to the forward condition. The restricted condition had higher compressive (p=0.025) and lower tensile (p=0.043) principal strains compared to the free condition. For the same magnitude of principal or shear strains, axial rotation and collateromotion angles were greatest for the restricted condition. Therefore, the increase in P1 principal compressive and shear bone strains associated with restricted foot slip indicate that alterations in foot:ground interaction may play a role in fracture occurrence in horses.

The foot-surface interaction and its impact on musculoskeletal adaptation and injury risk in the horse

The equine limb has evolved for efficient locomotion and high-speed performance, with adaptations of bone, tendon and muscle. However, the system lacks the ability seen in some species to dynamically adapt to different circumstances. The mechanical interaction of the limb and the ground is influenced by internal and external factors including fore-hind mass distribution, lead limb, moving on a curve, shoeing and surface properties. It is unclear which of the components of limb loading have the largest effect on injury and performance but peak load, impact and vibration all play a role. Factors related to the foot-ground interface that limit performance are poorly understood. Peak performance varies vastly between disciplines but at high speeds such as racing and polo, force and grip are key limits to performance.

Modeling equine race surface vertical mechanical behaviors in a musculoskeletal modeling environment

Race surfaces have been associated with the incidence of racehorse musculoskeletal injury, the leading cause of racehorse attrition. Optimal race surface mechanical behaviors that minimize injury risk are unknown. Computational models are an economical method to determine optimal mechanical behaviors. Previously developed equine musculoskeletal models utilized ground reaction floor models designed to simulate a stiff, smooth floor appropriate for a human gait laboratory. Our objective was to develop a computational race surface model (two force-displacement functions, one linear and one nonlinear) that reproduced experimental race surface mechanical behaviors for incorporation in equine musculoskeletal models. Soil impact tests were simulated in a musculoskeletal modeling environment and compared to experimental force and displacement data collected during initial and repeat impacts at two racetracks with differing race surfaces - (i) dirt and (ii) synthetic. Best-fit model coefficients (7 total) were compared between surface types and initial and repeat impacts using a mixed model ANCOVA. Model simulation results closely matched empirical force, displacement and velocity data (Mean R(2)=0.930-0.997). Many model coefficients were statistically different between surface types and impacts. Principal component analysis of model coefficients showed systematic differences based on surface type and impact. In the future, the race surface model may be used in conjunction with previously developed the equine musculoskeletal models to understand the effects of race surface mechanical behaviors on limb dynamics, and determine race surface mechanical behaviors that reduce the incidence of racehorse musculoskeletal injury through modulation of limb dynamics.

Validation of a laboratory method for evaluating dynamic properties of reconstructed equine racetrack surfaces

Background

Racetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior.

Objective

To develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties.

Methods

Track-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression.

Results

Most dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces.

Conclusions

Laboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD).

Potential Relevance

Dynamic impact properties of race surfaces can be evaluated in a laboratory setting, allowing for further study of factors affecting surface behavior under controlled conditions.