Differences in bone turnover markers and injury risks between local and international horses: A Victorian Spring Racing Carnival study.

BACKGROUND: Musculoskeletal injuries (MSI) are common in racehorses and have been of increasing concern in horses travelling internationally to compete. Understanding the differences in bone turnover between local horses and international horses following long-distance air transportation may inform MSI prevention strategies. OBJECTIVES: To understand the differences in bone turnover markers and risk of MSI between local horses and international horses following long-distance air transportation. STUDY DESIGN: Prospective cohort. METHODS: The concentrations of bone turnover markers (OCN and CTXI), markers of stress (cortisol), inflammation (serum amyloid A) and circadian rhythm (melatonin), and bisphosphonates were determined in blood samples collected twice (14-17 days apart), from horses following international travel (n = 69), and from local horses (n = 79). The associations between markers, long-distance travel and MSI were determined using multivariable generalised linear regression models. RESULTS: Within 3-5 days post-transport, concentrations of cortisol in international horses were higher than those of local horses (main effect, Coef. 0.39; 95% CI 0.24, 0.54; p < 0.001) but they decreased and were not different to those of local horses at the second timepoint (interaction effect, Coef. -0.27; 95% CI -0.46, -0.07; p = 0.007). After adjusting for age and sex, OCN and CTXI were not significantly different between international and local horses; however, OCN was lower in international horses at timepoint 2 (interaction effect, Coef. -0.16; 95% CI -0.31, -0.01; p = 0.043). The prevalence of MSI was higher in the international (26%; 95% CI 16, 38%) compared with local horses (8%; 95% CI 3, 16%; p < 0.001), with all severe MSI sustained by the international horses. At the second timepoint compared with the first timepoint post-transport, cortisol remained high or increased (interaction effect, Coef. 0.43; 95% CI 0.24, 0.61; p < 0.001) and OCN increased (interaction effect, Coef. 0.26; 95% CI 0.08, 0.44; p = 0.006) in the horses that sustained severe MSI. MAIN LIMITATIONS: Horse population and racing career parameters differed between groups. Bone turnover markers have low sensitivity to detect local bone changes. CONCLUSIONS: Most horses showed minimal effects of long-distance air transport within 2 weeks relative to local horses as assessed by stress and bone turnover markers. Screening for persistent high cortisol and evidence of net bone formation after long-distance air transportation may help to identify racehorses at high risk of catastrophic MSI.

CONTEXTE: Les blessures musculosquelettiques (MSI) sont communes chez les chevaux de course et demeurent une source d'inquiétude pour les chevaux voyageant à l'international. Comprendre les différences de remodelage osseux entre les chevaux locaux et ceux voyageant suivant un trajet aérien longue distance pourrait aider au développement de stratégies de prévention des dommages musculosquelettiques. OBJECTIFS: Comprendre les différences de marqueurs de remodelage osseux et de risques de MSI entre les chevaux locaux et ceux voyageant à l'international suivant un transport aérien de longue distance. TYPE D'ÉTUDE: Étude de cohorte prospective. MÉTHODES: Les concentrations des marqueurs de remodelage osseux (OCN et CTXI), de stress (cortisol), d'inflammation (serum amyloid A), de rythme circadien (melatonin) et les bisphosphonates ont été mesurés dans des échantillons sanguins à deux reprises (14­17 jours à part) chez des chevaux ayant été à l'international (n = 69) et étant restés localement (n = 79). L'association entre les marqueurs, le transport longue distance et les MSI a été déterminée par modèles de régression linéaire multivarié généralisé. RÉSULTATS: Entre 3 à 5 jours suivant le transport, les concentrations de cortisol chez les chevaux internationaux étaient supérieures aux chevaux locaux (effet primaire, Coef. 0.39; 95% CI 0.24, 0.54; P < 0.001), mais ont diminué par la suite jusqu'à ne plus être différent de ceux des chevaux locaux à la deuxième mesure (effet interaction, Coef. −0.27; 95% CI −0.46, −0.07; P = 0.007). Après ajustement pour l'âge et le sexe, OCN et CTXI n'étaient pas significativement différents entre les chevaux internationaux et locaux. Cependant, OCN était inférieur chez les chevaux internationaux à la deuxième mesure (effet interaction, Coef. −0.16; 95% CI −0.31, −0.01; P = 0.043). La prévalence de MSI était plus élevée chez les chevaux internationaux (26%; 95% CI 16, 38%) comparativement aux chevaux locaux (8%; 95% CI 3, 16%; p < 0.001), avec toutes les MSI sévères subi par les chevaux internationaux. Au moment de la deuxième mesure comparée à la première mesure après le transport, le cortisol est demeuré élevé ou a augmenté (effet interaction, Coef. 0.43; 95% CI 0.24, 0.61; P < 0.001) et l'OCN a augmenté (effet interaction, Coef. 0.26; 95% CI 0.08, 0.44; P = 0.006) chez les chevaux ayant subi une MSI sévère. LIMITES PRINCIPALES: La population équine et leurs paramètres de course diffèrent entre les groupes. Les marqueurs de remodelage osseux ont une faible sensibilité pour la détection de changements osseux localisés. CONCLUSION: En deux semaines, les effets de transport aérien longue distance ont été minimaux pour la majorité des chevaux comparativement aux chevaux locaux, tel que démontré par les marqueurs de stress et de remodelage osseux. La détection de niveau élevé de cortisol de façon persistante et d'évidence d'os néoformé suivant un transport aérien de longue distance pourrait aider à détecter les chevaux de course à haut risque de MSI.

Assessment of subchondral bone microdamage quantification using contrast-enhanced imaging techniques.

Bone microdamage is common at subchondral bone (SCB) sites subjected to repeated high rate and magnitude of loading in the limbs of athletic animals and humans. Microdamage can affect the biomechanical behaviour of bone under physiological loading conditions. To understand the effects of microdamage on the mechanical properties of SCB, it is important to be able to quantify it. The extent of SCB microdamage had been previously estimated qualitatively using plain microcomputed tomography (µCT) and a radiocontrast quantification method has been used for trabecular bone but this method may not be directly applicable to SCB due to differences in bone structure. In the current study, SCB microdamage detection using lead uranyl acetate (LUA) and quantification by contrast-enhanced µCT and backscattered scanning electron microscopy (SEM) imaging techniques were assessed to determine the specificity of the labels to microdamage and the accuracy of damaged bone volume metrices. SCB specimens from the metacarpus of racehorses, with the hyaline articular cartilage (HAC) removed, were grouped into two with one group subjected to ex vivo uniaxial compression loading to create experimental bone damage. The other group was not loaded to preserve the pre-existing in vivo propagated bone microdamage. A subset of each group was stained with LUA using an established or a modified protocol to determine label penetration into SCB. The µCT and SEM images of stained specimens showed that penetration of LUA into the SCB was better using the modified protocol, and this protocol was repeated in SCB specimens with intact hyaline articular cartilage. The percentage of total label localised to bone microdamage was determined on SEM images, and the estimated labelled bone volume determined by µCT in SCB groups was compared. Label was present around diffuse and linear microdamage as well as oblique linear microcracks present at the articular surface, except in microcracks with high-density mineral infills. Bone surfaces lining pores with recent mineralisation were also labelled. Labelled bone volume fraction (LV/BV) estimated by µCT was higher in the absence of HAC. At least 50% of total labels were localised to bone microdamage when the bone area fraction (B.Ar/T.Ar) of the SCB was greater than 0.85 but less than 30% when B.Ar/T.Ar of the SCB was less than 0.85. To adjust for LUA labels on bone surfaces, a measure of the LV/BV corrected for bone surface area (LV/BV BS-1 ) was used to quantify damaged SCB. In conclusion, removal of HAC and using a modified labelling protocol effectively stained damaged SCB of the metacarpus of racehorses and represents a technique useful for quantifying microdamage in SCB. This method can facilitate future investigations of the effects of microdamage on joint physiology.

The association between Thoroughbred racehorse training practices and musculoskeletal injuries in Victoria, Australia.

Catastrophic musculoskeletal injuries (CMI) in horses are associated with both too little and too much high-speed exercise. In order to advise trainers on training and management strategies that minimize the risk of musculoskeletal injury (MSI), a better understanding of how training practices affect MSI in racehorses is needed. Data from prospective studies relating training data and MSI are complicated by the gradual development of pathology and the effect of this on the ability of horses to train consistently prior to the identification of an injury. To circumvent this, 66 Australian Thoroughbred trainers were surveyed on their intended training practices, including rest, pre-training, and race-fit practices. Associations between intended training practices and catastrophic and non-catastrophic race day MSI outcomes in two-year-old and mature (≥three-year-old) horses were assessed using multivariable negative binomial regression models. The incidence of two-year-old race day MSI was lower for trainers who preferred shorter times (weeks) to trial, less time in fast work pre-trial (p = 0.003), shorter, more frequent rest periods (p < 0.01) and higher amounts of fast work at 15.5-16.7 m/s once race-fit (p = 0.001). The incidence of mature horse race day MSI was lower for trainers who preferred longer rest periods (p = 0.026) and a high-volume pre-trial training strategy comprising a high volume of slower speed gallop training and longer times to trial compared to fast and light training programs (p = 0.004) for their mature horses, in addition to higher amounts of fast work at 15.5-16.7 m/s for their race-fit two-year-olds (p = 0.012). Race day CMI incidence was lower for trainers who preferred lower volumes of fast gallop work for their race-fit mature horses (p < 0.05). These results suggest that two-year-old training practices could affect MSI risk later in a horse's career, and that age and stage in training (pre-trial, race-fit) are important considerations when developing training practices to minimize the risk of MSI.

Poor Association between Facial Expression and Mild Lameness in Thoroughbred Trot-Up Examinations.

Musculoskeletal injuries in racehorses are difficult to detect prior to catastrophic breakdown. Lameness is commonly attributed to orthopaedic pain in horses, therefore, subtle lameness may be a pre-clinical sign of injury and, if identified early, could allow for preventative intervention. Our objective was to determine if facial expressions could be used to detect mild lameness as an indicator of orthopaedic pain in 'fit to race' horses. The Horse Grimace Scale (HGS) and the facial expressions in ridden horses (FEReq), were used to score images (n = 380) of mildly lame (n = 21) and non-lame (n = 17) Thoroughbred horses by two independent observers. Using an Equinosis Lameness Locator®, the lameness status of each horse was determined according to published thresholds [forelimb lameness (>|14.5 mm|) and hindlimb lameness (>|7.5 mm|)]. Inter and intraobserver reliability were assessed using two-way random-effects models. Univariable associations between lameness and facial expression parameters were identified using logistic and linear regression. Interobserver reliability was moderate (κ 0.45; 95% CI 0.36, 0.55). Horses with moderate mouth strain (HGS) and tense and extended upper lip (FEReq) were less likely to be lame (p = 0.042 and p = 0.027, respectively). Exposed sclera was associated with lameness (p = 0.045). Higher orbital tightening (HGS) scores were associated with a lower degree of maximum head amplitude (HDmax) lameness (p = 0.044). Tension and moderate tension above the eye, for the HGS and FEReq scores, were associated with increasing amplitude of HDmax (p = 0.048 and p = 0.034, respectively). Inconsistent associations between lameness status and HGS and FEReq scores may limit the potential use of the facial expression for the prediction of mild orthopaedic pain during pre-race lameness examinations. More objective parameters associated with mild orthopaedic pain should be explored.

Validation of inertial measurement units to detect and predict horse behaviour while stabled.

BACKGROUND: Musculoskeletal injuries are observed in Thoroughbred racehorses and may become catastrophic. Currently, there are limited methods for early detection of such injuries. Most injuries develop gradually due to accumulated damage, providing the opportunity for early detection. Horses experiencing pain or lameness may exhibit changes in behaviour so the development of an objective, real-time system monitoring horse behaviour may enable detection of bone injuries before catastrophic failure. OBJECTIVES: To determine whether intensive observational methods of assessing horse behaviour can be replaced by use of inertial measurement units (IMUs). STUDY DESIGN: Validation study assessing IMU use against video observation. METHODS: Six hospitalised Thoroughbreds (algorithm training data) and 19 Thoroughbred racehorses in-training (algorithm testing data) were equipped with an IMU placed on the lateral side of both forelimbs (left fore, LF; right fore, RF) and monitored in a stable for 4 h. An algorithm was developed to classify behaviour and then validated against video recordings. RESULTS: Standing was the most prevalent behaviour (LF 88.8%, 95% confidence interval [CI] 88.7-89.0; RF 88.5%, 95% CI 88.4-88.7). IMU classification of recumbent and standing activities showed excellent agreement (sensitivity) with video observation (>98%). This was followed by stepping (LF 89.4%, RF 85.5%) then weight-shifting (LF 54.3%, RF 61.5%). Predictions from the algorithm showed misclassification of 2.5% (LF 5500/225 352, RF 5218/210 170). Excluding standing, misclassification was 6.8% (1705/25 158) and 7.5% (1812/24 077) for the left and right forelimbs, respectively, with pawing and weight-shifting most frequently misclassified. MAIN LIMITATIONS: Increasing the number of horses and types of behaviours observed may improve predictions. CONCLUSIONS: IMUs displayed a high sensitivity to movement on a small number of horses, and with further validation they have the potential to effectively monitor behaviour of racehorses in training. However, more sensitive methods may be needed to validate the classification of weight-shifting behaviour. Future studies should evaluate the association between each behaviour and musculoskeletal injury.

Changes in Thoroughbred speed and stride characteristics over successive race starts and their association with musculoskeletal injury.

BACKGROUND: Certain stride characteristics have been shown to affect changes in biomechanical factors that are associated with injuries in human athletes. Determining the relationship between stride characteristics and musculoskeletal injury (MSI) may be key in limiting injury occurrence in the racehorse. OBJECTIVES: This study aimed to determine whether changes in race day speed and stride characteristics over career race starts are associated with an increased risk of MSI in racehorses. STUDY DESIGN: Case-control study. METHODS: Speed, stride length, and stride frequency data were obtained from the final 200 m sectional of n = 5660 race starts by n = 584 horses (case n = 146, control n = 438). Multivariable joint models, combining longitudinal and survival (time to injury) analysis, were generated. Hazard ratios and their 95% confidence intervals (CI) are presented. RESULTS: The risk of MSI increased by 1.18 (95% CI 1.09, 1.28; P < 0.001) for each 0.1 m/s decrease in speed and by 1.11 (95% CI 1.02, 1.21; P = 0.01) for each 10 cm decrease in stride length over time (career race starts). A more marked rate of decline in speed and stride length was observed approximately 6 races prior to injury. Risk of MSI was highest early in the horse's racing career. MAIN LIMITATIONS: Only final sectional stride characteristics were assessed in the model. The model did not account for time between race starts. CONCLUSIONS: Decreasing speed and stride length over multiple races is associated with MSI in racehorses. Monitoring stride characteristics over time may be beneficial for the early detection of MSI.

Effects of in vivo fatigue-induced microdamage on local subchondral bone strains.

Biomechanical strain is a major stimulus of subchondral bone (SCB) tissue adaptation in joints but may also lead to initiation and propagation of microcracks, highlighting the importance of quantifying the intratissue strain in subchondral bone. In the present study, we used micro computed tomography (µCT) imaging, mechanical testing, and digital image correlation (DIC) techniques to evaluate the biomechanical strains in equine SCB under impact compression applied through the articular surface. We aimed to investigate the effects of in vivo accumulated microdamage in equine SCB on the distribution of mechanical impact strain through the articular cartilage. Under the applied strain of 2.0 ± 0.1% (mean ± standard deviation, n=15) to the articular surface of cartilage-bone plugs, the overall thickness of the SCB developed eSCBOverall = 0.7 ± 0.2% in all specimens. Contours of high strains in specimens without microdamage (NDmg) aligned parallel to the cartilage-bone interface with peak tensile, ϵt, and compressive, ϵc, strains of 0.5 ± 0.3% and 1.2 ± 0.4%, respectively at the time of peak compression (n=7). In damaged specimens (Dmg), contours of high strains aligned with the cracks in the imaged plane with peak strains of ϵt= 1.2 ± 0.8% and ϵc= 3.5 ± 2.2%, respectively (n=7). Microdamage was the main predictor of the normalised compressive and tensile strains across the SCB thickness. Results of multivariable analyses revealed presence of microdamage, distance from the articular surface and TMD were the main predictors of normalised compressive and tensile strain. Strain was greater in the superficial bone, particularly for specimens with microdamage. In vivo fatigue-induced microdamage is an important predictor of local subchondral bone strains.

Use of a novel helical fan beam imaging system for computed tomography of the distal limb in sedated standing horses: 167 cases (2019-2020).

OBJECTIVE: To evaluate the diagnostic capabilities of a novel helical fan beam CT system used for imaging of horses with a range of clinical distal limb problems. ANIMALS: 167 horses. PROCEDURES: Medical records were reviewed of horses presented for CT of the distal limb at 2 university-based veterinary hospitals. The following data were recorded: age, sex, breed, presenting complaint, sedation used for imaging, scanning time, procedure time, other diagnostic imaging methods performed, imaging diagnosis, clinical diagnosis, and complications during imaging. RESULTS: Most horses were Thoroughbreds and Quarter Horses. Procedure times ranged from 15 to 40 minutes, with scanning completed in 15 to 45 seconds for each region of interest. The foot or pastern region was commonly scanned (88/167 [53%] horses), with navicular bone disease diagnosed in 42 of 88 (48%) horses. The fetlock region was also commonly scanned (42/167 [40%] horses), with palmar or plantar osteochondral disease diagnosed in 17 of 42 (40%) horses. Horses were compliant during scanning, and no complications with sedation or damage to the scanner occurred. A specific imaging diagnosis for the lameness was achieved more frequently with CT imaging (166/167 [99%]) than with planar digital radiography (26/58 [45%]). CLINICAL RELEVANCE: The helical fan beam CT system could be used safely to scan sedated standing horses from the carpal or tarsal region distally. Subjectively, the machine was easy to operate, allowing CT to be incorporated into lameness investigations. CT imaging was very likely to result in a clinical diagnosis in horses with distal limb lameness.

Use of a novel helical fan beam imaging system for computed tomography of the head and neck in sedated standing horses: 120 cases (2019-2020).

OBJECTIVE: To evaluate the diagnostic capabilities of a novel helical fan beam CT system used for imaging of horses with clinical problems of the head and neck. ANIMALS: 120 horses. PROCEDURES: Medical records were reviewed of horses presented for CT of the head or neck at 2 university hospitals. The following data were recorded: age, sex, breed, presenting complaint, sedation used for imaging, scanning time, procedure time, other diagnostic imaging methods performed, imaging diagnosis, clinical diagnosis, and complications during imaging. RESULTS: Quarter Horses and Warmbloods were the most common breeds, and the most common complaint was nasal discharge. The head (101/120 [84%] horses) was scanned most frequently, and the most common diagnoses were primary dental disease and a space-occupying lesion of the paranasal sinuses. Nuchal bursitis was the most common imaging diagnosis in the neck region. Procedure time ranged from 20 to 45 minutes with a scanning time of 30 to 40 seconds. No complications with horse sedation occurred, and horses tolerated scanning well. An imaging diagnosis was more frequently achieved with CT (109/120 [91%] horses) than with planar digital radiography (23/61 [38%] horses). CLINICAL RELEVANCE: The helical fan beam CT system had fast scanning times and could be used safely for routine imaging of the teeth and sinuses in horses. The caudal extent of scanning in the neck region was limited by the shape of the horse's neck and thorax.

Biomechanical and Microstructural Properties of Subchondral Bone From Three Metacarpophalangeal Joint Sites in Thoroughbred Racehorses.

Fatigue-induced subchondral bone (SCB) injury is common in racehorses. Understanding how subchondral microstructure and microdamage influence mechanical properties is important for developing injury prevention strategies. Mechanical properties of the disto-palmar third metacarpal condyle (MCIII) correlate poorly with microstructure, and it is unknown whether the properties of other sites within the metacarpophalangeal (fetlock) joint are similarly complex. We aimed to investigate the mechanical and structural properties of equine SCB from specimens with minimal evidence of macroscopic disease. Three sites within the metacarpophalangeal joint were examined: the disto-palmar MCIII, disto-dorsal MCIII, and proximal sesamoid bone. Two regions of interest within the SCB were compared, a 2 mm superficial and an underlying 2 mm deep layer. Cartilage-bone specimens underwent micro-computed tomography, then cyclic compression for 100 cycles at 2 Hz. Disto-dorsal MCIII specimens were loaded to 30 MPa (n = 10), while disto-palmar MCIII (n = 10) and proximal sesamoid (n = 10) specimens were loaded to 40 MPa. Digital image correlation determined local strains. Specimens were stained with lead-uranyl acetate for volumetric microdamage quantification. The dorsal MCIII SCB had lower bone volume fraction (BVTV), bone mineral density (BMD), and stiffness compared to the palmar MCIII and sesamoid bone (p < 0.05). Superficial SCB had higher BVTV and lower BMD than deeper SCB (p < 0.05), except at the palmar MCIII site where there was no difference in BVTV between depths (p = 0.419). At all sites, the deep bone was stiffer (p < 0.001), although the superficial to deep gradient was smaller in the dorsal MCIII. Hysteresis (energy loss) was greater superficially in palmar MCIII and sesamoid (p < 0.001), but not dorsal MCIII specimens (p = 0.118). The stiffness increased with cyclic loading in total cartilage-bone specimens (p < 0.001), but not in superficial and deep layers of the bone, whereas hysteresis decreased with the cycle for all sites and layers (p < 0.001). Superficial equine SCB is uniformly less stiff than deeper bone despite non-uniform differences in bone density and damage levels. The more compliant superficial layer has an important role in energy dissipation, but whether this is a specific adaptation or a result of microdamage accumulation is not clear.

Relationship between Thoroughbred workloads in racing and the fatigue life of equine subchondral bone.

Fatigue life (FL) is the number of cycles of load sustained by a material before failure, and is dependent on the load magnitude. For athletes, 'cycles' translates to number of strides, with load proportional to speed. To improve previous investigations estimating workload from distance, we used speed (m/s, x) per stride collected using 5 Hz GPS/800 Hz accelerometer sensors as a proxy for limb load to investigate factors associated with FL in a Thoroughbred race start model over 25,234 race starts, using a combination of mathematical and regression modelling. Fore-limb vertical force (NKg-1) was estimated using a published equation: Vertical force = 2.778 + 2.1376x - 0.0535x2. Joint load (σ) was estimated based on the vertical force, scaled according to the maximum speed and defined experimental loads for the expected variation in load distribution across a joint surface (54-90 MPa). Percentage FL (%FL) was estimated using a published equation for cycles to failure (Nf) summed across each race start: Nf = 10(σ-134.2)/-14.1. Multivariable mixed-effects linear regression models were generated on %FL, adjusting for horse-level clustering, presented as coefficients; 95%CI. Scaled to the highest joint load, individual starts accrued a mean of 9.34%FL (sd. 1.64). Older age (coef. 0.03; 0.002-0.04), longer race-distances (non-linear power transformed), and firmer track surfaces (ref. Heavy 10: Good 3 coef. 2.37; 2.26-2.48) were associated with greater %FL, and males accrued less than females (p < 0.01). Most variables associated with %FL are reported risk factors for injury. Monitoring strides in racehorses may therefore allow identification of horses at risk, enabling early detection of injury.

Catastrophic Musculoskeletal Injuries in Thoroughbred Racehorses in Uruguay, 2011-2017.

Catastrophic musculoskeletal injuries (CMI) pose a major welfare concern to horses and their riders, yet limited data are available describing their occurrence in South America. Using a retrospective cohort and case-control design, the objective of the study was to determine the incidence of CMI for Thoroughbreds in training and racing, and associated horse-level risk factors in Uruguay. Seventy-seven Thoroughbreds sustained a CMI, 37 of which were age- and sex-matched to 111 control horses in the same race. Training and racing data from 2011 to 2017 were collected. Incidence of race day CMI per 1,000 race starts and training CMI incidence per 100 horse months were calculated using Poisson regression. Univariable logistic regression was used to assess relationships between race history and occurrence of CMI by fracture location, and multivariable for all fracture locations. Overall race day incidence of CMI was 0.42 per 1,000 race starts (95% CI 0.29, 0.60). The incidence of CMI in training was 0.059 per 100 horse months. Twenty-nine percent (22/77) of horses that sustained a CMI had not raced prior. Most fractures were of the forelimbs (80.3%). There were 32 (41.6%) distal and 39 (50.6%) proximal limb fractures. The risk of CMI was greater for horses with fewer places (P = .001), and greater time between the previous race and the race in which CMI occurred (P = .020). The rate of race day CMI was low, despite Uruguay being a racing jurisdiction with policies and risk factors associated with greater CMI rates compared to other jurisdictions. Lightly raced horses with long periods since their previous race start should be monitored closely.

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.

Association of Thoroughbred Racehorse Workloads and Rest Practices with Trainer Success.

Understanding the relationship between the training practices of Thoroughbred racehorses and race performance is important to ensure advice given to trainers for injury prevention or management is practical and consistent. We assessed associations between intended volume and speed of gallop training (i.e., typical workloads for horses free of injury or other performance limiting conditions) and rest practices on official trainer career and previous season success rates (rate of wins and places, prizemoney per start). Sixty-six Australian Thoroughbred trainers were surveyed. Multivariable negative binomial regression models were employed for the outcomes career and previous season wins and places, and linear regression models for prizemoney per start. Intended training workload was not associated with prizemoney. Pre-trial total galloping distances (≥13.3 m/s) between 7500 m and 15,000 m were associated with a higher rate of career wins, and previous season wins and places per start (p < 0.05). Slow-speed (13.3-14.3 m/s) galloping distance to trial between 5000 m to 12,500 m was associated with higher rate of career placings per start, with reduced performance over 12,500 m (p = 0.003). Greater time between race starts was associated with a greater rate of previous season wins and prizemoney per start until three weeks between starts, with decline in performance thereafter (p < 0.05). Greater frequency of rest breaks was associated with greater prizemoney per start earnt in the previous season (p ≤ 0.01). These results suggest that modifications to training programs aimed at injury prevention, such as avoiding long galloping distances, should not adversely affect trainer success.

Variation in GPS and accelerometer recorded velocity and stride parameters of galloping Thoroughbred horses.

BACKGROUND: With each stride, galloping horses generate large skeletal loads which influence bone physiology, and may contribute to musculoskeletal injury. Horse speed and stride characteristics are related, but the usefulness of using horse speed and distance travelled as a proxy for stride characteristics is unknown. OBJECTIVES: We aimed to determine stride characteristics, their variance and their relationship with speed in horses performing maximally. STUDY DESIGN: Retrospective cross-sectional analysis of archived data. METHODS: Stride characteristics obtained using GPS and inertial sensors in Thoroughbred horses were retrieved. Data per 200 m race segment ('sectionals') for horses competing in races (N = 25,259 race starts) were analysed to determine if speed predicted stride parameters. Multivariable mixed-effects linear regression models were fitted. RESULTS: Mean (±SD) stride length, stride count (number of strides per 200 m), duration and speed were 7.08 ± 0.39 m, 28.32 ± 1.56 strides/200 m, 0.43 ± 0.02 s/stride and 16.63 ± 1.04 m/s across all sectionals and starts. Speed and stride length decreased, and stride count increased with race progression (P < 0.001). Male sex, greater race distance, better finishing position and firmer track surfaces were associated with less strides per 200 m and longer stride durations. MAIN LIMITATIONS: Lack of an independent party validation of the measurement system used in this study. CONCLUSIONS: There was a substantial inter-horse variation in stride parameters, with speed predicting half or less of this variation. Speed alone does not fully explain stride characteristics in horses. Future studies aimed at investigating the impact of gait on bone biology and pathology would benefit from accounting for stride characteristics (eg length and duration).

Effects of in vivo fatigue-induced subchondral bone microdamage on the mechanical response of cartilage-bone under a single impact compression.

Subchondral bone (SCB) microdamage is prevalent in the joints of human athletes and animals subjected to high rate and magnitude cyclic loading of the articular surface. Quantifying the effect of such focal in vivo fatigue-induced microdamage on the mechanical response of the tissue is critical for the understanding of joint surface injury and the development of osteoarthritis. Thus, we aimed to quantify the mechanical properties of cartilage-bone from equine third metacarpal (MC3) condyles, which is a common area of accumulated microdamage due to repetitive impact loading. We chose a non-destructive technique, i.e. high-resolution microcomputed tomography (µCT) imaging, to identify various degrees of in vivo microdamage in SCB prior to mechanical testing; because µCT imaging can only identify a proportion of accumulated microdamage, we aimed to identify racing and training history variables that provide additional information on the prior loading history of the samples. We then performed unconfined high-rate compression of approximately 2% strain at 45%/s strain rate to simulate a cycle of gallop and used real-time strain measurements using digital image correlation (DIC) techniques to find the stiffness and shock absorbing ability (relative energy loss) of the cartilage-bone unit, and those associated with cartilage and SCB. Results indicated that stiffness of cartilage-bone and those associated with the SCB decreased with increasing grade of damage. Whole specimen stiffness also increased, and relative energy loss decreased with higher TMD, whereas bone volume fraction of the SCB was only associated negatively with the stiffness of the bone. Overall, the degree of subchondral bone damage observed with µCT was the main predictor of stiffness and relative energy loss of the articular surface of the third metacarpal bone of Thoroughbred racehorses under impact loading.

The relationship between microstructure, stiffness and compressive fatigue life of equine subchondral bone.

Subchondral bone injuries often precede articular cartilage damage in osteoarthritis and are common in thoroughbred racehorses due to the accumulation of fatigue damage from high speed racing and training. Thus, racehorses provide a model to investigate the role of subchondral bone in joint disease. We assessed the association of horse and racing related factors and micro-CT based micromorphology of three separate subchondral bone layers with the initial stiffness and compressive fatigue life of bone plugs. Furthermore, we investigated three different definitions of fatigue failure of subchondral bone during compressive fatigue testing. Initial stiffness was 2,362 ±â€¯443 MPa (mean ±â€¯standard deviation). Median compressive fatigue life during cyclic loading to -78 MPa was 16,879 (range 210 to 57,064). Subchondral bone stiffness increased over a median of 24% (range 3%-42%) of fatigue life to a maximum of 3,614 ±â€¯635 MPa. Compressive fatigue life was positively associated with bone volume fraction in the deeper layers of subchondral bone, maximal stiffness, and the number of cycles to maximal stiffness. Initial stiffness was positively associated with tissue mineral density in the deeper layers and bone volume fraction in the superficial layer. Most specimens with a fatigue life of less than 5,500 cycles fractured grossly before reaching 30% reduction of maximal stiffness. Cycles to 10% reduction of maximal stiffness correlated strongly with cycles to lowest recorded stiffness at gross fracture and thus is a valid alternative failure definition for compressive fatigue testing of subchondral bone. Our results show that subchondral bone sclerosis as a result of high speed exercise and measured as bone volume fraction is positively associated with compressive fatigue life and thus has a protective effect on subchondral bone. Further research is required to reconcile this finding with the common collocation of fatigue damage in sclerotic subchondral bone of racehorses.

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.

Subchondral bone morphology in the metacarpus of racehorses in training changes with distance from the articular surface but not with age.

The repetitive large loads generated during high-speed training and racing commonly cause subchondral bone injuries in the metacarpal condyles of racehorses. Adaptive bone modelling leads to focal sclerosis at the site of highest loading in the palmar aspect of the metacarpal condyles. Information on whether and how adaptive modelling of subchondral bone changes during the career of a racehorse is sparse. The aim of this cross-sectional study was to describe the changes in subchondral bone micromorphology in the area of highest loading in the palmar aspect of the metacarpal condyle in thoroughbred racehorses as a function of age and training. Bone morphology parameters derived from micro-CT images were evaluated using principal component analysis and mixed-effects linear regression models. The largest differences in micromorphology were observed in untrained horses between the age of 16 and 20 months. Age and duration of a training period had no influence on tissue mineral density, bone volume fraction or number and area of closed pores to a depth of 5.1 mm from the articular surface in 2- to 4-year-old racehorses in training. Horses with subchondral bone injuries had more pores in cross-section compared with horses without subchondral bone injuries. Differences in bone volume fraction were due to the volume of less mineralised bone. Tissue mineral density increased and bone volume fraction decreased with increasing distance from the articular surface up to 5.1 mm from the articular surface. Further research is required to elucidate the biomechanical and pathophysiological consequences of these gradients of micromorphological parameters in the subchondral bone.