Can quantitative computed tomography detect bone morphological changes associated with catastrophic proximal sesamoid bone fracture in Thoroughbred racehorses?

Selection of density standard and X-ray tube settings for computed digital absorptiometry in horses using the k-means clustering algorithm

BACKGROUND

In veterinary medicine, conventional radiography is the first-choice method for most diagnostic imaging applications in both small animal and equine practice. One direction in its development is the integration of bone density evaluation and artificial intelligence-assisted clinical decision-making, which is expected to enhance and streamline veterinarians' daily practices. One such decision-support method is k-means clustering, a machine learning and data mining technique that can be used clinically to classify radiographic signs into healthy or affected clusters. The study aims to investigate whether the k-means clustering algorithm can differentiate cortical and trabecular bone in both healthy and affected horse limbs. Therefore, identifying the optimal computed digital absorptiometry parameters was necessary.

METHODS AND RESULTS

Five metal-made density standards, made of pure aluminum, aluminum alloy (duralumin), cuprum alloy, iron-nickel alloy, and iron-silicon alloy, and ten X-ray tube settings were evaluated for the radiographic imaging of equine distal limbs, including six healthy limbs and six with radiographic signs of osteoarthritis. Density standards were imaged using ten combinations of X-ray tube settings, ranging from 50 to 90 kV and 1.2 to 4.0 mAs. The relative density in Hounsfield units was firstly returned for both bone types and density standards, then compared, and finally used for clustering. In both healthy and osteoarthritis-affected limbs, the relative density of the long pastern bone (the proximal phalanx) differed between bone types, allowing the k-means clustering algorithm to successful differentiate cortical and trabecular bone.

CONCLUSION

Density standard made of duralumin, along with the 60 kV, 4.0 mAs X-ray tube settings, yielded the highest clustering metric values and was therefore considered optimal for further research. We believe that the identified optimal computed digital absorptiometry parameters may be recommended for further researches on the relative quantification of conventional radiographs and for distal limb examination in equine veterinary practice.

Prospective, longitudinal assessment of subchondral bone morphology and pathology using standing, cone-beam computed tomography in fetlock joints of 2-year-old Thoroughbred racehorses in their first year of training

BACKGROUND

Catastrophic injuries of the fetlock joints occur in Thoroughbred racehorses and are preceded by stress-induced bone injury. Early detection of subchondral bone injury is essential to prevent irreversible damage or bone failure.

OBJECTIVES

To investigate the use of standing, robotic cone-beam computed tomography (CBCT) for assessing longitudinal changes in subchondral bone morphology and pathology of the fetlock joints associated with race training in young Thoroughbreds.

STUDY DESIGN

Observational cohort study.

METHODS

Forty-one 2-year-old Thoroughbred racehorses were recruited prior to the start of race training. Standing CBCT and radiographs of all 4 metacarpo-/metatarsophalangeal (MCP/MTP) joints were obtained at 0, 6 and 12 months. Hyperdensity, as an estimate of subchondral bone sclerosis, was measured in the distal third metacarpal (MC3)/metatarsal (MT3) bone and proximal phalanx (P1) at each time point on computed tomography. CBCTs were examined for subchondral bone pathology consisting of areas of hypodensity within regions of hyperdensity.

RESULTS

Subchondral bone sclerosis increased significantly over time in the medial and lateral MC3/MT3 condyles and in the medial and lateral parasagittal grooves of MC3/MT3. The presence of subchondral bone pathology increased significantly over time in the medial and lateral palmar condyles of MC3/MT3, the lateral parasagittal groove, the medial dorsal condyle and the medial and lateral ridges of P1.

MAIN LIMITATIONS

There was attrition of horses due to relocation, change in ownership, and retirement from racing. Husbandry, training regimens and racing schedules were not controlled for in the study.

CONCLUSIONS

Standing CBCT is an efficient and effective screening tool for assessing subchondral bone morphology and identifying pathology of the fetlock joint in young Thoroughbred racehorses. CBCT may facilitate early detection of bone pathology allowing for timely intervention and prevention of more serious injuries.

Fractures in Thoroughbred racing and the potential for pre-race identification of horses at risk

Risk rates for and predisposing factors to fractures occurring in Thoroughbred racing that have been published in peer reviewed journals are documented. The potential for currently available techniques to identify horses at increased risk for fracture is discussed on the bases of principles, practicalities, advantages, disadvantages and current data. All are reviewed in light of justifiable decision making and importance of fractures to horseracing's social license.

Magnetic Resonance Imaging, Computed Tomographic and Radiographic Findings in the Metacarpophalangeal Joints of 40 Non-Lame Thoroughbred Yearlings

Most catastrophic injuries in Thoroughbred racehorses involve the fetlock. There is no description of comparative imaging in Thoroughbreds entering racehorse training. The aim was to describe MRI, CT and radiographic findings in the metacarpophalangeal joint of non-lame Thoroughbred yearlings. Forty Thoroughbreds underwent low-field MRI, fan-beam CT and radiographic examinations of both metacarpophalangeal joints. Images were assessed subjectively. A hypoattenuating lesion of the sagittal ridge of the third metacarpal bone (McIII) was identified in 33/80 limbs in CT reconstructions. Cone-shaped mineralisation in the sagittal ridge was detected in MR images (n = 17) and in CT images (n = 5). Mild hyperattenuation was common in trabecular bone in the dorsomedial (36/80) and palmarolateral (25/80) metacarpal condyles in CT reconstructions. A focal lesion in the subchondral bone was seen in the proximal phalanx (n = 19) and in McIII (n = 11). Enlarged vascular channels were detected in the metacarpal condyles in 57/80 limbs and in the proximal sesamoid bones in all limbs. Signs of bone modelling are seen in yearling Thoroughbred fetlocks. Sagittal ridge lesions were common and are likely associated with osteochondrosis or other developmental osteochondral defects. Focal lesions in the subchondral bone of McIII and proximal phalanx can indicate developmental abnormalities or subtle subchondral bone injuries.

Clinical predictive models in equine medicine: A systematic review

Clinical predictive models use a patient's baseline demographic and clinical data to make predictions about patient outcomes and have the potential to aid clinical decision making. The extent of equine clinical predictive models is unknown in the literature. Using PubMed and Google Scholar, we systematically reviewed the predictive models currently described for use in equine patients. Models were eligible for inclusion if they were published in a peer-reviewed article as a multivariable model used to predict a clinical/laboratory/imaging outcome in an individual horse or herd. The agreement of at least two authors was required for model inclusion. We summarised the patient populations, model development methods, performance metric reporting, validation efforts, and, using the Predictive model Risk of Bias Assessment Tool (PROBAST), assessed the risk of bias and applicability concerns for these models. In addition, we summarised the index conditions for which models were developed and provided detailed information on included models. A total of 90 predictive models and 9 external validation studies were included in the final systematic review. A plurality of models (41%) was developed to predict outcomes associated with colic, for example, need for surgery or survival to discharge. All included models were at high risk of bias, defined as failing one or more PROBAST signalling questions, primarily for analysis-related reasons. Importantly, a high risk of bias does not necessarily mean that models are unusable, but that they require more careful consideration prior to clinical use. Concerns about applicability were low for the majority of models. Systematic reviews such as this can serve to increase veterinarians' awareness of predictive models, including evaluation of their performance and their use in different patient populations.

Metacarpophalangeal Joint Pathology and Bone Mineral Density Increase with Exercise but Not with Incidence of Proximal Sesamoid Bone Fracture in Thoroughbred Racehorses

Proximal sesamoid bone (PSB) fracture is the leading cause of fatal musculoskeletal injury in Thoroughbred racehorses in Hong Kong and the US. Efforts are underway to investigate diagnostic modalities that could help identify racehorses at increased risk of fracture; however, features associated with PSB fracture risk are still poorly understood. The objectives of this study were to (1) investigate third metacarpal (MC3) and PSB density and mineral content using dual-energy X-ray absorptiometry (DXA), computed tomography (CT), Raman spectroscopy, and ash fraction measurements, and (2) investigate PSB quality and metacarpophalangeal joint (MCPJ) pathology using Raman spectroscopy and CT. Forelimbs were collected from 29 Thoroughbred racehorse cadavers (n = 14 PSB fracture, n = 15 control) for DXA and CT imaging, and PSBs were sectioned for Raman spectroscopy and ash fraction measurements. Bone mineral density (BMD) was greater in MC3 condyles and PSBs of horses with more high-speed furlongs. MCPJ pathology, including palmar osteochondral disease (POD), MC3 condylar sclerosis, and MC3 subchondral lysis were greater in horses with more high-speed furlongs. There were no differences in BMD or Raman parameters between fracture and control groups; however, Raman spectroscopy and ash fraction measurements revealed regional differences in PSB BMD and tissue composition. Many parameters, including MC3 and PSB bone mineral density, were strongly correlated with total high-speed furlongs.

Radiomics Modeling of Catastrophic Proximal Sesamoid Bone Fractures in Thoroughbred Racehorses Using μCT

Proximal sesamoid bone (PSB) fractures are the most common musculoskeletal injury in race-horses. X-ray CT imaging can detect expressed radiological features in horses that experienced catastrophic fractures. Our objective was to assess whether expressed radiomic features in the PSBs of 50 horses can be used to develop machine learning models for predicting PSB fractures. The μCTs of intact contralateral PSBs from 50 horses, 30 of which suffered catastrophic fractures, and 20 controls were studied. From the 129 intact μCT images of PSBs, 102 radiomic features were computed using a variety of voxel resampling dimensions. Decision Trees and Wrapper methods were used to identify the 20 top expressed features, and six machine learning algorithms were developed to model the risk of fracture. The accuracy of all machine learning models ranged from 0.643 to 0.903 with an average of 0.754. On average, Support Vector Machine, Random Forest (RUS Boost), and Log-regression models had higher performance than K-means Nearest Neighbor, Neural Network, and Random Forest (Bagged Trees) models. Model accuracy peaked at 0.5 mm and decreased substantially when the resampling resolution was greater than or equal to 1 mm. We find that, for this in vitro dataset, it is possible to differentiate between unfractured PSBs from case and control horses using μCT images. It may be possible to extend these findings to the assessment of fracture risk in standing horses.

Cetaceans Humerus Radiodensity by CT: A Useful Technique Differentiating between Species, Ecophysiology, and Age

Cetaceans are mammals that underwent a series of evolutionary adaptations to live in the aquatic environment, including morphological modifications of various anatomical structures of the skeleton and their bone mineral density (BMD); there are few studies on the latter. BMD is related to the radiodensity measured through computed tomography (CT) in Hounsfield units (HU). This work aimed to test and validate the usefulness of studying humeral bone radiodensity by CT of two cetacean species (the Atlantic spotted dolphin and the pygmy sperm whale) with different swimming and diving habits. The radiodensity was analysed at certain levels following a new protocol based on a review of previous studies. Humeral radiodensity values were related to four aspects: species, diving behaviour, swimming activity level, and age. We observed that the consistent differences in the radiodensity of the cortical bone of the distal epiphysis between animals of different life-history categories suggest that this bone portion could be particularly useful for future ontogenetic studies. Hence, this technique may be helpful in studying and comparing species with different ecophysiologies, particularly distinguishing between swimming and diving habits.

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.

Proximal sesamoid bone microdamage is localized to articular subchondral regions in Thoroughbred racehorses, with similar fracture toughness between fracture and controls

OBJECTIVE

To determine whether proximal sesamoid bone (PSB) microdamage and fracture toughness differ between Thoroughbred racehorses sustaining PSB fracture and controls.

STUDY DESIGN

Cadaveric case-control.

ANIMALS

Twenty-four Thoroughbred racehorses (n = 12 PSB fracture, n = 12 control).

METHODS

Proximal sesamoid bones were dissected, and gross pathological changes and morphological measurements were documented. High-speed exercise history data were evaluated. Microdamage was assessed in fracture, fracture-contralateral limb (FXCL) and control PSBs using whole bone lead uranyl acetate (LUA) staining with micro-CT imaging or basic fuchsin histological analysis. Fracture toughness mechanical testing was carried out in 3-point-bending of microbeams created from PSB flexor cortices. Data were analyzed using ordinal logistic and linear regression models.

RESULTS

Microdamage was detected most commonly in the articular subchondral region of PSBs via LUA micro-CT and basic fuchsin histology. There were no differences in microdamage between FXCL and control PSBs. Fracture toughness values were similar for FXCL (1.31 MPa√m) and control (1.35 MPa√m) PSBs. Exercise histories were similar except that horses sustaining fracture spent a greater percentage of their careers in rest weeks.

CONCLUSION

Microdamage was detected in the articular region of PSBs but was not greater in horses sustaining catastrophic PSB fracture. Fracture toughness of PSB flexor cortices did not differ between FXCL and control PSBs.

CLINICAL SIGNIFICANCE

Although uncommon, microdamage is localized to the articular region of Thoroughbred racehorse PSBs. Catastrophic PSB failure is not associated with lower PSB flexor cortex fracture toughness.

When radiography and ultrasonography are not enough: the use of computed tomography and magnetic resonance imaging for equine lameness cases

MRI and CT have enhanced our diagnostic abilities for equine lameness beyond what is available using radiography and ultrasonography. This has allowed veterinarians to better prognosticate and treat lameness conditions, improving patient outcomes. This article discusses the basic principles behind MRI and CT, their advantages and disadvantages, the different types of equipment available for clinical use in horses, the typical diagnostic workup prior to pursuing advanced imaging, and common regions where MRI and CT are used clinically. The companion Currents in One Health by Spriet, AJVR, July 2022, discusses even more advanced equine imaging in the form of positron emission tomography. Combined, these future directions of MRI, CT, and positron emission tomography may include improved ability to image standing horses or screen for injury prevention.

Survival Analysis of Training Methodologies and Other Risk Factors for Musculoskeletal Injury in 2-Year-Old Thoroughbred Racehorses in Queensland, Australia

Musculoskeletal injuries remain a global problem for the Thoroughbred racing industry and there is conflicting evidence regarding the effect of age on the incidence of injuries. The ideal time to commence race training is strongly debated, with limited supporting literature. There is also conflicting evidence regarding the effect of high-speed exercise on musculoskeletal injuries. There is a strong interest in developing training and management strategies to reduce the frequency of injuries. The types of musculoskeletal injuries vary between 2-year-old and older horses, with dorsal metacarpal disease the most common injury in 2-year-old horses. It is likely that risk factors for injury in 2-year-old horses are different than those for older horses. It is also likely that the risk factors may vary between types of injury. This study aimed to determine the risk factors for musculoskeletal injuries and dorsal metacarpal disease. We report the findings of a large scale, prospective observational study of 2-year-old horses in Queensland, Australia. Data were collected weekly for 56-weeks, from 26 trainers, involving 535 2-year-old Thoroughbred racehorses, 1, 258 training preparations and 7, 512-weeks of exercise data. A causal approach was used to develop our statistical models, to build on the existing literature surrounding injury risk, by incorporating the previously established causal links into our analyses. Where previous data were not available, industry experts were consulted. Survival analyses were performed using Cox proportional hazards or Weibull regression models. Analysis of musculoskeletal injuries overall revealed the hazard was reduced with increased exposure to high-speed exercise [Hazard ratio (HR) 0.89, 95% Confidence Interval (CI) 0.84, 0.94, p < 0.001], increased number of training preparations (HR 0.58, 95% CI 0.50, 0.67, p < 0.001), increased rest before the training preparation (HR 0.89, 95% CI 0.83, 0.96, p = 0.003) and increased dam parity (HR 0.86, 95% CI 0.77, 0.97, p = 0.01). The hazard of injury was increased with increasing age that training commenced (HR 1.13, 95% CI 1.06, 1.19, p < 0.001). Analyses were then repeated with the outcome of interest dorsal metacarpal disease. Factors that were protective against dorsal metacarpal disease and musculoskeletal injuries overall included: increased total cumulative distance (HR 0.89, 95% CI 0.82, 0.97, p = 0.001) and total cumulative days exercised as a gallop (HR 0.96, 95% CI 0.92, 0.99, p = 0.03), the number of the training preparations (HR 0.43, 95% CI 0.30, 0.61, p < 0.001). The age that training commenced was harmful for both dorsal metacarpal disease (HR 1.17, 95% CI 1.07, 1.28, p < 0.001 and overall musculoskeletal injuries.). The use of non-ridden training modalities was protective for dorsal metacarpal disease (HR 0.89, 95% CI 0.81, 0.97, p = 0.008), but not musculoskeletal injuries overall. The male sex increased the hazard of DMD compared to females (HR 2.58, 95% CI 1.20, 5.56, p = 0.02), but not MSI overall. In summary, the hazard of musculoskeletal injury is greatest for 2-year-old horses that are born from uniparous mares, commence training at a later age, are in their first training preparation, have undertaken little high-speed exercise or had limited rest before their training preparation. The hazard of dorsal metacarpal disease is greatest for 2-year-old horses that are males, commence training at a later age, are in their first training preparation, have undertaken little high-speed exercise or had limited use of non-ridden training modalities. Close monitoring of these high-risk horses during their training program could substantially reduce the impact of MSI. Furthermore, an understanding of how training methodologies affect the hazard of MSI facilitates modification of training programs to mitigate the risk impact of injury. The strengths of this study include a large sample size, a well-defined study protocol and direct trainer interviews. The main limitation is the inherent susceptibility to survival bias.

Factors Associated with Fatality in Ontario Thoroughbred Racehorses: 2003-2015

Simple Summary

Ontario’s Alcohol and Gaming Commission records equine racing fatalities through its Equine Health Program. This study examines the 695 Thoroughbred occurrences from 2003 to 2015 with the aim of identifying associations. Deaths occurred within 60 days of a horse racing or being entered or qualified to race. Calculated on the most commonly adopted basis, rates for Ontario Thoroughbreds are high—2.94/1000 starts (all fatalities) and 1.96/1000 (breakdowns only), compared with a global industry breakdown range of 0.29–2.36/1000 starts. The study revealed several significant risk factors, including workload, stage of training, age, sex, stage of career, finish position, race field size, and day of week. Among fatalities were groups where combinations of these risk factors were important, such as being a two-year-old male, un-castrated, and in early training. Probability of fatality fell over the study period in response to increasing awareness through existence of the Program and adoption of new regulations, but remains of concern. All identified associations represent aspects of management and industry structure that are amenable to change with a view to reducing fatalities. A link between fatality and cumulative, non-fatal outcomes should also be considered. An overall approach might view associated factors as sources of physical and psychological stress that, acutely and cumulatively, may influence the liability for adverse outcomes in training and racing.

Abstract

Ontario’s Alcohol and Gaming Commission records equine racing fatalities through its Equine Health Program. The present study examined all Thoroughbred fatalities from 2003 to 2015, inclusive, to identify associations. Official records and details of fatalities were combined in multivariable logistic regression modelling of 236,386 race work-events (433 fatalities), and 459,013 workout work-events (252 fatalities). Fatality rates were 2.94/1000 race starts (all fatalities) and 1.96/1000 (breakdowns only) with an overall rate of 2.61% or 26.1 fatalities/1000 horses. Comparison with published reports reveals rates to be high. Musculoskeletal injury was the predominant complaint and there was a high incidence of horses dying suddenly. Liability was high for young horses early in the season with a differential according to sex and whether a male horse was gelded. Horses undertaking repeated workouts had a higher liability and liability was higher in workouts for horses switching from dirt/synthetic to turf racing and for young horses in sprints. Race distance was not significant but high fatality rates in some large field, distance races combined with effects of age and workload identified groups at particular risk. As field size increased, fatality liability increased for early-finishing horses. Findings suggest jockey strategy could be an important factor influencing fatalities. Probability of fatality declined over the study period. Findings indicate that rapid accumulation of workload in animals early in their preparation is likely to be damaging. Fatality fell toward the end of a season and for horses with a long career history of successful performance; however, horses not exhibiting this robustness and staying power represent the population of greatest concern. Associations may be characterised as representing sources of stress, current or cumulative, and identifying at-risk animals on this basis may be as productive as targeting specific, discrete mechanisms suspected to contribute to individual fatalities.

Determination of correlation of proximal sesamoid bone osteoarthritis with high-speed furlong exercise and catastrophic sesamoid bone fracture in Thoroughbred racehorses

OBJECTIVE

To examine whether proximal sesamoid bone (PSB) articular cartilage and bone osteoarthritic changes or palmar osteochondral disease (POD) scores were associated with exercise history and catastrophic PSB fracture in Thoroughbred racehorses.

SAMPLES

PSBs from 16 Thoroughbred racehorses (8 with and 8 without PSB fracture).

PROCEDURES

Exercise history was collected, and total career high-speed furlongs was used as the measure of total exercise per horse. At necropsy, medial and lateral condyles of the third metacarpus from each forelimb were assigned a POD score, followed by imaging with micro-CT for evaluation of osteophyte size. Three investigators that were blinded to the type of PSB (fracture or no fracture) used the Osteoarthritis Research Society International (OARSI) scoring system to evaluate acellularity, chondrocyte necrosis, cartilage fibrillation, chondrone formation, safranin O stain uptake, and tidemark advancement of 1 central sagittal tissue section/PSB (4 PSBs/horse). Cartilage thickness and bone necrosis were scored on the basis of histologic examination.

RESULTS

POD score, osteophyte size score, percentage of bone necrosis, tidemark advancement, chondrone formation, and total OARSI score were greater in horses with more accrued total career high-speed furlongs. Scores for POD, osteophyte size, fibrillation, acellularity, chondrone formation, and total OARSI were greater for horses with PSB fracture.

CONCLUSIONS AND CLINICAL REVELANCE

OARSI scoring revealed that more advanced osteoarthritic changes strongly correlated with total career high-speed furlongs and PSB fracture. However, the effect of exercise was dominant, suggesting that exercise history will be important to include in future models that aim to assess risk factors for catastrophic PSB fracture.

Factors Associated with Mortality in Ontario Standardbred Racing: 2003-2015

Simple Summary

Racing provides employment and career engagement, is passionately pursued, and helps sustain our close relationship with horses, but it can also be associated with injury and losses. Fatalities occur on and off racetracks, involving welfare concerns, economic impact, and damage to racing’s public profile and social license. Musculoskeletal injury, the most visible loss, represents only one source and remains poorly understood, while for other losses and off-track mortality little is known. In 2003, the Province of Ontario, Canada introduced a registry for racehorse mortalities, providing opportunities to better understand losses and contributing factors. Following an earlier publication describing losses across all breeds, this paper presents analysis of standardbred mortality and relationships with routine management and competition. Results reveal that aspects of industry structure may contribute to mortality, and that the impact might be anticipated by close monitoring of a horse’s profile and performance. The immediate circumstances precipitating any specific fatality should be seen as separate from this underlying environmental liability. This has implications for how future research might be conducted and findings interpreted. It is hoped the present study can be used to decrease mortality and cumulative injury so as to reduce losses and strengthen societal support for racing.

Abstract

Factors associated with mortality in standardbred racehorses were assessed through a retrospective annualized cohort study of all-cause mortality from 2003–2015 (n = 978) (identified in the Ontario Racehorse Death Registry). Race and qualifying data for official work-events were also gathered (1,778,330 work-events, 125,200 horse years). Multivariable logistic regression analysis revealed sex, age, and indices of workload and intensity and their interactions to be strongly associated with mortality. Track class, race versus qualifying performance, and work-event outcome (finish position, scratched, or failed to finish) also influenced mortality odds, which increased as performance slowed. Intense competition at higher performance levels and qualifying races at lower levels carried particularly high odds. Though occurring frequently, musculoskeletal injury was less frequent than all other presenting problems combined. Industry structure contributes to mortality through interaction between horse characteristics and the competition environment. This substrate may be amenable to management to minimize liability, but incident-specific triggers may represent chance factors and be relatively difficult to identify or control. Differentiating between substrate and trigger when studying specific clinical problems may provide greater clarity and yield in identifying underlying causes. Mortality may reflect a continuum of circumstances, cumulative impacts of which might be identified before a fatal event occurs.

The Risk Factors for Musculoskeletal Injuries in Thoroughbred Racehorses in Queensland, Australia: How These Vary for Two-Year-Old and Older Horses and with Type of Injury

Simple Summary

Musculoskeletal injuries (MSI) continue to affect Thoroughbred racehorses internationally, despite over thirty years of research into this problem. Studies of risk factors for musculoskeletal injuries report inconsistent findings. Consequently, developing training strategies to mitigate the risk of MSI is difficult. We identified factors associated with particularly high odds of injury in this population of racehorses. Two-year-old horses from primiparous mares (first foals born) are at increased odds of MSI, particularly dorsal metacarpal disease (“shinsoreness”). Two-year-old horses that have had a total preparation length of between 10 and 14 weeks also have increased odds of injury. Horses of all ages that travelled a total distance of 2.4–3.8 km (12–19 furlongs) at a gallop (faster than 15 m/s; 13 s/furlong; 900 m/min; 55 km/h) in the last four weeks and horses three years and older that travelled 3.0–4.8 km (15–24 furlongs) at three-quarter pace and above (faster than 13 m/s; 15 s/furlong; 800 m/min; 48 km/h) also have increased odds of injury. We recommend that these horses should be monitored closely for impending signs of injury. We also observed a non-linear relationship between high-speed exercise and musculoskeletal injuries. This highlights the importance of high-speed exercise to enable tissue adaptation to training. Finally, in some situations, increasing the number of days worked at a slow pace may be more effective for preventing MSI, if horses are perceived at a higher risk, than resting the horse altogether. Early identification of horses at increased risk of injury and appropriate intervention could substantially reduce the impact of musculoskeletal injuries in Thoroughbred racehorses.

Abstract

Musculoskeletal injuries (MSI) continue to affect Thoroughbred racehorses internationally. There is a strong interest in developing training and management strategies to reduce their impact, however, studies of risk factors report inconsistent findings. Furthermore, many injuries and fatalities occur during training rather than during racing, yet most studies report racing data only. By combining racing and training data a larger exposure to risk factors and a larger number of musculoskeletal injuries are captured and the true effect of risk factors may be more accurately represented. Furthermore, modifications to reduce the impact of MSI are more readily implemented at the training level. Our study aimed to: (1) determine the risk factors for musculoskeletal injuries and whether these are different for two-year-old and older horses and (2) determine whether risk factors vary with type of injury. This was performed by repeating analyses by age category and injury type. Data from 202 cases and 202 matched controls were collected through weekly interviews with trainers and analysed using conditional logistic regression. Increasing dam parity significantly reduced the odds of injury in horses of all age groups because of the effect in two-year-old horses (odds ratio (OR) 0.08; 95% confidence interval (CI) 0.02, 0.36; p < 0.001). Increasing total preparation length is associated with higher odds of injury in horses of all ages (OR 5.56; 95% CI 1.59, 19.46; p = 0.01), but particularly in two-year-old horses (OR 8.05; 95% CI 1.92, 33.76; p = 0.004). Increasing number of days exercised at a slow pace decreased the odds of injury in horses of all ages (OR 0.09; 95% CI 0.03, 0.28; p < 0.001). The distance travelled at three-quarter pace and above (faster than 13 m/s; 15 s/furlong; 800 m/min; 48 km/h) and the total distance travelled at a gallop (faster than 15 m/s; 13 s/furlong; 900 m/min; 55 km/h) in the past four weeks significantly affected the odds of injury. There was a non-linear association between high-speed exercise and injury whereby the odds of injury initially increased and subsequently decreased as accumulated high-speed exercise distance increased. None of the racing career and performance indices affected the odds of injury. We identified horses in this population that have particularly high odds of injury. Two-year-old horses from primiparous mares are at increased odds of injury, particularly dorsal metacarpal disease. Two-year-old horses that have had a total preparation length of between 10 and 14 weeks also have increased odds of injury. Horses of all ages that travelled a total distance of 2.4–3.8 km (12–19 furlongs) at a gallop in the last four weeks and horses three years and older that travelled 3.0–4.8 km (15–24 furlongs) at three-quarter pace and above also have increased odds of injury. We recommend that these horses should be monitored closely for impending signs of injury. Increasing the number of days worked at a slow pace may be more effective for preventing injury, if horses are perceived at a higher risk, than resting the horse altogether. Early identification of horses at increased risk and appropriate intervention could substantially reduce the impact of musculoskeletal injuries in Thoroughbred racehorses.

Validation of standing cone beam computed tomography for diagnosing subchondral fetlock pathology in the Thoroughbred racehorse

BACKGROUND

Subchondral bone pathology is common in Thoroughbred racehorses and believed to precede more serious injury. Early identification of pathology is critical to allow for intervention.

OBJECTIVES

To determine interobserver variability of fetlock subchondral bone lesions using cone beam and fan beam computed tomography (CBCT, FBCT) and to validate a robotics-controlled CBCT to identify fetlock subchondral bone pathology in the Thoroughbred racehorse.

STUDY DESIGN

Prospective cohort study.

METHODS

FBCT and CBCT images were acquired of 25 metacarpo-/metatarsophalangeal joints of Thoroughbred racehorses. Images were analysed for subchondral bone lesions commonly identified in Thoroughbred fetlocks by an imaging specialist and surgery specialist. Interobserver and intermodality equivalence were determined with a Pearson correlation analysis and Bland-Altman equivalence test.

RESULTS

Interobserver FBCT correlation was significant (P < .05) for 19 of 25 variables (Pearson R mean 0.77). Concordance was significant for all 25 variables (Bland Altman average difference 0.28 ± 0.21 mm). Interobserver CBCT correlation was significant for 21 of 25 variables (Pearson R mean 0.73). Concordance was significant for all variables (Bland Altman average difference 0.07 ± 1.90 mm). Intermodality (FBCT vs CBCT) correlation and concordance was significant for all variables as interpreted by the radiologist (Pearson R mean of 0.72, Bland Altman average difference 0.21 ± 0.47 mm). Intermodality correlation was significant for 19 of 25 variables as interpreted by the surgeon (Pearson R mean of 0.72). Concordance was significant for all variables (Bland Altman average difference 0.49 ± 0.52 mm).

MAIN LIMITATIONS

Neither FBCT nor CBCT images were compared with other imaging modalities/histopathology; limited number of cases included; inconsistent agreement of small lesions in specific categories.

CONCLUSIONS

Standing CBCT is a valid diagnostic modality to identify subchondral bone lesions in Thoroughbred fetlocks. This technology may provide valuable information regarding the development and progression of fetlock pathology and yield insight into predisposing factors leading to more severe pathology.

Microstructural properties of the proximal sesamoid bones of Thoroughbred racehorses in training

BACKGROUND

Proximal sesamoid bone fractures are common catastrophic injuries in racehorses. Understanding the response of proximal sesamoid bones to race training can inform fracture prevention strategies.

OBJECTIVES

To describe proximal sesamoid bone microstructure of racehorses and to investigate the associations between microstructure and racing histories.

STUDY DESIGN

Cross-sectional.

METHODS

Proximal sesamoid bones from 63 Thoroughbred racehorses were imaged using micro-computed tomography. Bone volume fraction (BVTV) and bone material density (BMD) of the whole bone and four regions (apical, midbody dorsal, midbody palmar and basilar) were determined. Generalised linear regression models were used to identify the associations between bone parameters and race histories of the horses.

RESULTS

The mean sesamoid BVTV was 0.79 ± 0.08 and BMD was 806.02 ± 24.66 mg HA/ccm. BVTV was greater in medial sesamoids compared with lateral sesamoids (0.80 ± 0.07 vs 0.79 ± 0.08; P < .001) predominantly due to differences in the apical region (medial-0.76 ± 0.08 vs lateral-0.72 ± 0.07; P < .001). BVTV in the midbody dorsal region (0.86 ± 0.06) was greater than other regions (midbody palmar-0.79 ± 0.07, basilar-0.78 ± 0.06 and apical-0.74 ± 0.08; P < .001). BVTV was greater in sesamoids with more microcracks on their articular surface (Coef. 0.005; 95% CI 0.001, 0.009; P = .01), greater extent of bone resorption on their abaxial surface (Grade 2-0.82 ± 0.05 vs Grade 1-0.80 ± 0.05 or Grade 0-0.79 ± 0.06; P = .006), in horses with a low (0.82 ± 0.07) or mid handicap rating (0.78 ± 0.08) compared with high rating (0.76 ± 0.07; P < .001), in 2- to 5-year-old horses (0.81 ± 0.07) compared with younger (0.68 ± 0.08) or older horses (0.77 ± 0.08; P < .001) and in horses that commenced their racing career at less than 4 years of age (0.79 ± 0.08 vs 0.77 ± 0.77; P < .001). BMD was greater in the midbody dorsal (828.6 ± 19.6 mg HA/ccm) compared with other regions (apical-805.8 ± 21.8, midbody palmar-804.7 ± 18.4 and basilar-785.0 ± 17.1; P < .001), in horses with a handicap rating (low-812.1 ± 20.0, mid-821.8 ± 21.3 and high-814.6 ± 19.4) compared with those with no rating (791.08 ± 24.4, P < .001), in females (806.7 ± 22.0) and geldings (812.2 ± 22.4) compared with entires (792.7 ± 26.2; P = .02) and in older horses (<2-year-old-763.7 ± 24.8 vs 2- to 5-year-old-802.7 ± 23.4, and 6- to 12-year-old-817.8 ± 20.0; P = .002).

MAIN LIMITATIONS

Data were cross-sectional.

CONCLUSIONS

Densification of the proximal sesamoid bones is associated with the commencement of racing in younger horses and the presence of bone fatigue-related pathology. Lower sesamoid BVTV was associated with longevity and better performance.

A radiomics platform for computing imaging features from µCT images of Thoroughbred racehorse proximal sesamoid bones: Benchmark performance and evaluation

BACKGROUND

Proximal sesamoid bone (PSB) fractures are the most common fatal musculoskeletal injury in North American racehorses. Computed tomography has the potential to detect morphological changes in bone structure but can be challenging to analyse reliably and quantitatively.

OBJECTIVES

To develop a radiomics platform that allows the comparison of features from micro-CTs (µCT) of PSBs in horses that sustained catastrophic fractures with horses that did not. To compare features calculated with a radiomics approach with features calculated from a previously published study that used quantitative µCT in the same specimens.

STUDY DESIGN

Retrospective study of cadaver specimens of µCT images of PSBs using prospectively applied radiomics.

METHODS

Radiomics features were computed on standardised CT datasets to benchmark the software. Features from µCT images of PSBs from eight horses that sustained PSB fracture and eight controls were computed using the contralateral, intact forelimb from horses sustaining PSB fracture (cases, n = 19) and all available forelimbs for controls (n = 30). Two-hundred and fifteen radiomic features were calculated, and similar or comparable features were compared with those reported in a previous study that used the same specimens.

RESULTS

Morphologic features computed with the radiomics approach, such as volume, minor axis dimensions and anisotropy were highly correlated with previously published data. A high number of imperceptible radiomic features, such as entropy, coarseness and histogram features were also found to be significantly different (P < .01). The extent of the differences in image features for the cases and controls PSBs depends on radiomic calculation settings.

MAIN LIMITATIONS

Only datasets obtained from cadaver specimens were included in the study.

CONCLUSIONS

A radiomics approach for analysing µCT images of PSBs was able to identify and reproduce differences in image features in cases and controls. Furthermore, radiomics revealed many more imperceptible image features between cases and control PSBs.

Associations between the radiographic appearance of vascular channels in proximal sesamoid bones, their microstructural characteristics and past racing performance in Thoroughbreds

BACKGROUND

Abnormalities in vascular channel appearance within the proximal sesamoid bone (PSB) are the most common findings in Thoroughbred yearling presale radiographs and are often evaluated on radiographs of adult racehorses. Despite this, their pathogenesis and clinical significance are poorly understood, and associations with racing performance are inconsistent.

OBJECTIVES

To determine microstructural characteristics of the PSBs associated with the radiographic appearance of vascular channels using microcomputed tomography (µCT) and to determine associations with past racing performance in mature horses.

STUDY DESIGN

Cross-sectional.

METHODS

One pair of PSBs were isolated from a forelimb of 59 Thoroughbred racehorses undergoing post-mortem examination. Each PSB (n = 118) was radiographed, assigned a vascular channel grade using previously published and novel grading systems, then imaged using µCT. Associations between radiographic, µCT and performance variables were investigated with uni- and multivariable generalised linear models.

RESULTS

All PSBs had at least one vascular channel (mean 3.6 ± 0.89) observed on µCT originating from the abaxial border, yet in only 63.6% (75/118) were channels observed radiographically. Proximal sesamoid bones with a higher bone volume fraction (odds ratio [OR] 1.08; 95% confidence interval [CI] 1.01-1.15; P = .03) and wider channel diameter (mm) on µCT (OR 20.67; 95% CI 3.29-130.00; P = .001) were more likely to have vascular channels identified on radiographs. Greater radiographic channel number (OR 0.96; 95% CI 0.92-1.00; P = .04) and channel diameter (mm; OR 0.96; 95% CI 0.92-1.00; P = .04) were associated with fewer career placings.

MAIN LIMITATIONS

Radiographs of isolated bones avoided the normal superimposition of tissue encountered in the live horse.

CONCLUSIONS

The ability to identify vascular channels radiographically indicates widening of channels and densification of the PSB. More radiographic channels and greater channel diameter were associated with similar or poorer measures of past performance, suggesting that these changes are not desirable.