Pathology of the distal condyles of the third metacarpal and third metatarsal bones of the horse

Identification of a global gene expression signature associated with the genetic risk of catastrophic fracture in iPSC-derived osteoblasts from Thoroughbred horses

Bone fractures are a significant problem in Thoroughbred racehorses. The risk of fracture is influenced by both genetic and environmental factors. To determine the biological processes that are affected in genetically susceptible horses, we utilised polygenic risk scoring to establish induced pluripotent stem cells (iPSCs) from horses at high and low genetic risk. RNA-sequencing on iPSC-derived osteoblasts revealed 112 genes that were significantly differentially expressed. Forty-three of these genes have known roles in bone, 27 are not yet annotated in the equine genome and 42 currently have no described role in bone. However, many of the proteins encoded by the known and unknown genes have reported interactions. Functional enrichment analyses revealed that the differentially expressed genes were overrepresented in processes regulating the extracellular matrix and pathways known to be involved in bone remodelling and bone diseases. Gene set enrichment analysis also detected numerous biological processes and pathways involved in glycolysis with the associated genes having a higher expression in the iPSC-osteoblasts from horses with low polygenic risk scores for fracture. Therefore, the differentially expressed genes may be relevant for maintaining bone homeostasis and contribute to fracture risk. A deeper understanding of the consequences of mis-regulation of these genes and the identification of the DNA variants which underpin their differential expression may reveal more about the molecular mechanisms which are involved in equine bone health and fracture risk.

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.

Condylar fracture location is correlated to exercise history in Thoroughbred racehorses

BACKGROUND

Condylar fractures are a major cause of morbidity and mortality in Thoroughbred racehorses. Condylar fractures have a variety of fracture configurations that suggest there may be differences in aetiopathogenesis.

OBJECTIVE

To determine if exercise history differs with condylar fracture location in a population of Thoroughbred racehorses.

STUDY DESIGN

Retrospective analysis of clinical and exercise data.

METHODS

Exercise history of Thoroughbred racehorses that had condylar fracture repair between 1 January 2018 and 28 February 2021 was compared between racehorses that had fractures located radiographically either within the parasagittal groove (PSG) or abaxial to the PSG (non-PSG). Age, sex, and last event (race, timed work) matched control groups were compared between the PSG and non-PSG groups. Additionally, exercise history variables of both groups were each compared with a group-specific control population, each consisting of three control racehorses of equivalent age and sex matched to each affected racehorse by last event (race or official timed work) before fracture.

RESULTS

Eighty-two horses with 84 fractures (45 PSG, 39 non-PSG) met inclusion criteria. Age was not different between groups (PSG: 3.4 ± 1.3 years [mean ± SD], non-PSG: 3.7 ± 1.3, p = 0.3). Number of races (PSG: 5.3 ± 7.1, non-PSG: 11.4 ± 8.9, p < 0.001), total race furlongs (PSG: 38.2 ± 54.7, non-PSG: 79.2 ± 64, p = 0.003), and number of active days (PSG: 304 ± 224, non-PSG: 488 ± 314, p = 0.003) before fracture were greater; while mean number of layups was fewer (PSG: 1.0 ± 1.2, non-PSG: 0.5 ± 0.7, p = 0.02) in horses with non-PSG fracture. Horses with non-PSG fracture had more differences compared with their respective control group than horses with PSG fractures. Outcomes following fracture repair were not different between groups.

MAIN LIMITATIONS

Retrospective study, one regional racehorse population, two-dimensional imaging and potential inherent bias for fracture localisation, low statistical power for return to performance analysis.

CONCLUSIONS

Thoroughbred racehorses with non-PSG condylar fractures have a more extensive exercise history than horses with PSG condylar fractures, suggesting differences in fracture aetiopathogenesis.

Advancements in Subchondral Bone Biomechanics: Insights from Computed Tomography and Micro-Computed Tomography Imaging in Equine Models

PURPOSE OF REVIEW

This review synthesizes recent advancements in understanding subchondral bone (SCB) biomechanics using computed tomography (CT) and micro-computed tomography (micro-CT) imaging in large animal models, particularly horses.

RECENT FINDINGS

Recent studies highlight the complexity of SCB biomechanics, revealing variability in density, microstructure, and biomechanical properties across the depth of SCB from the joint surface, as well as at different joint locations. Early SCB abnormalities have been identified as predictive markers for both osteoarthritis (OA) and stress fractures. The development of standing CT systems has improved the practicality and accuracy of live animal imaging, aiding early diagnosis of SCB pathologies. While imaging advancements have enhanced our understanding of SCB, further research is required to elucidate the underlying mechanisms of joint disease and articular surface failure. Combining imaging with mechanical testing, computational modelling, and artificial intelligence (AI) promises earlier detection and better management of joint disease. Future research should refine these modalities and integrate them into clinical practice to enhance joint health outcomes in veterinary and human medicine.

A machine learning approach to identify stride characteristics predictive of musculoskeletal injury, enforced rest and retirement in Thoroughbred racehorses

Decreasing speed and stride length over successive races have been shown to be associated with musculoskeletal injury (MSI) in racehorses, demonstrating the potential for early detection of MSI through longitudinal monitoring of changes in stride characteristics. A machine learning (ML) approach for early detection of MSI, enforced rest, and retirement events using this same horse-level, race-level, and stride characteristic data across all race sectionals was investigated. A CatBoost model using features from the two races prior to an event had the highest classification performance (sensitivity score for MSI, enforced rest and retirement equal to 0.00, 0.58, 0.76, respectively and balanced accuracy score corresponding to 0.44), with scores decreasing for models incorporating windows that included additional races further from the event. Feature importance analysis of ML models demonstrated that retirement was predicted by older age, poor performance, and longer racing career, enforced rest was predicted by younger age and better performance, but was less likely to occur when the stride length is increasing, and MSI predicted by increased number of starters, greater variation in speed and lower percentage of career time at rest. A relatively low classification performance highlights the difficulties in discerning MSI from alternate events using ML. Improved data recording through more thorough assessment and annotation of adverse events is expected to improve the predictability of MSI.

Incidence and risk factors for limb fracture in greyhound racing in Western Australia

Identification of risk factors for race day injury can improve greyhound welfare. Race day fractures are the most significant injury event and have the greatest negative impact on dog welfare and the industry's social license to operate. This study aimed to describe the incidence and risk factors for race-related fractures in greyhounds racing in Western Australia. Electronic extracts describing race level data and race day injuries were provided by Racing and Wagering Western Australia (RWWA). The incidence rate (IR) of fractures for all greyhound race starts in Western Australia from 1 January 2017-31/12/2023 was calculated per 1000 starts. Univariable and multivariable models using Poisson regression were used to calculate the IR ratio of fracture type based on race and greyhound-level factors. There were 198,008 racing starts and 662 (n = 643, 97.1% involving the limbs) fractures resulting in an IR of 3.3 fractures per 1000 starts (95%CI 3.1-3.6). Greyhounds that had an injury in their previous race were 2.3 times (95%CI1.4-4.3) more likely to have a forelimb fracture than greyhounds that did not have an injury (P = 0.013). The risk of tarsal bone fracture was greater in greyhounds older than 30 months and greyhounds that had not raced in the previous 15 days. Risk factors for fractures in the forelimb were associated with trauma after interference or dog collisions, whereas tarsal fractures were associated with strain and cyclic loading from race training/racing. Changes to racing structure, rules and policies based on these risk factors may help to reduce fracture incidence in racing greyhounds.

Characterization and quantification of in-vitro equine bone resorption in 3D using μCT and deep learning-aided feature segmentation

High cyclic strains induce formation of microcracks in bone, triggering targeted bone remodeling, which entails osteoclastic resorption. Racehorse bone is an ideal model for studying the effects of high-intensity loading, as it is subject to focal formation of microcracks and subsequent bone resorption. The volume of resorption in vitro is considered a direct indicator of osteoclast activity but indirect 2D measurements are used more often. Our objective was to develop an accurate, high-throughput method to quantify equine osteoclast resorption volume in μCT 3D images. Here, equine osteoclasts were cultured on equine bone slices and imaged with μCT pre- and postculture. Individual resorption events were then isolated and analyzed in 3D. Modal volume, maximum depth, and aspect ratio of resorption events were calculated. A convolutional neural network (CNN U-Net-like) was subsequently trained to identify resorption events on post-culture μCT images alone, without the need for pre-culture imaging, using archival bone slices with known resorption areas and paired CTX-I biomarker levels in culture media. 3D resorption volume measurements strongly correlated with both the CTX-I levels (p < 0.001) and area measurements (p < 0.001). Our 3D analysis shows that the shapes of resorption events form a continuous spectrum, rather than previously reported pit and trench categories. With more extensive resorption, shapes of increasing complexity appear, although simpler resorption cavity morphologies (small, rounded) remain most common, in acord with the left-hand limit paradigm. Finally, we show that 2D measurements of in vitro osteoclastic resorption are a robust and reliable proxy.

Subchondral bone fatigue injury in the parasagittal condylar grooves of the third metacarpal bone in thoroughbred racehorses elevates site-specific strain concentration

Condylar stress fracture of the distal end of the third metacarpal/metatarsal (MC3/MT3) bones is a major cause of Thoroughbred racehorse injury and euthanasia worldwide. Functional adaptation to exercise and fatigue damage lead to structural changes in the subchondral bone that include increased modeling (resulting in sclerotic bone tissue) and targeted remodeling repair (resulting in focal resorption spaces in the parasagittal groove). Whether these focal structural changes, as detectable by standing computed tomography (sCT), lead to elevated strain at the common site of condylar stress fracture has not been demonstrated. Therefore, the goal of the present study was to compare full-field three-dimensional (3D) strain on the distopalmar aspect of MC3 bone specimens with and without focal subchondral bone injury (SBI). Thirteen forelimb specimens were collected from racing Thoroughbreds for mechanical testing ex vivo and underwent sCT. Subsequently, full-field displacement and strain at the joint surface were determined using stereo digital image correlation. Strain concentration was observed in the parasagittal groove (PSG) of the loaded condyles, and those with SBI in the PSG showed higher strain rates in this region than control bones. PSG strain rate in condyles with PSG SBI was more sensitive to CT density distribution in comparison with condyles with no sCT-detectable injury. Findings from this study help to interpret structural changes in the subchondral bone due to fatigue damage and to assess risk of incipient stress fracture in a patient-specific manner.

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.

Histological and Histopathological Features of the Third Metacarpal/Tarsal Parasagittal Groove and Proximal Phalanx Sagittal Groove in Thoroughbred Horses with Racing History

Information regarding the histopathology of the proximal phalanx (P1) sagittal groove in racehorses is limited. Twenty-nine cadaver limbs from nine Thoroughbred racehorses in racing/race-training underwent histological examination. Histological specimens of the third metacarpal/metatarsal (MC3/MT3) parasagittal grooves and P1 sagittal grooves were graded for histopathological findings in hyaline cartilage (HC), calcified cartilage (CC), and subchondral plate and trabecular bone (SCB/TB) regions. Histopathological grades were compared between (1) fissure and non-fissure locations observed in a previous study and (2) dorsal, middle, and palmar/plantar aspects. (1) HC, CC, and SCB/TB grades were more severe in fissure than non-fissure locations in the MC3/MT3 parasagittal groove (p < 0.001). SCB/TB grades were more severe in fissure than non-fissure locations in the P1 sagittal groove (p < 0.001). (2) HC, CC, and SCB/TB grades including SCB collapse were more severe in the palmar/plantar than the middle aspect of the MC3/MT3 parasagittal groove (p < 0.001). SCB/TB grades including SCB collapse were more severe in the dorsal and middle than the palmar/plantar aspect of the P1 sagittal groove (p < 0.001). Histopathology in the SCB/TB region including bone fatigue injury was related to fissure locations, the palmar/plantar MC3/MT3 parasagittal groove, and the dorsal P1 sagittal groove.

Lesion Distribution in the Metacarpophalangeal and Metatarsophalangeal Region of 341 Horses Using Standing Magnetic Resonance Imaging

Pain localised to the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) region represents a frequent cause of lameness in sport horses, and standing magnetic resonance imaging (MRI) of these regions is increasingly being acquired. This multicentre retrospective study describes the ranges of abnormalities identified on standing MRI of the MCP/MTP region and compares patterns of abnormalities between forelimbs, hindlimbs and different sports disciplines. In total, 341 MRI reports were reviewed. Subchondral bone plate irregularities, condylar and proximal phalanx pathologies were frequently identified with subchondral bone defect, sclerosis and increased intensity on STIR images often described. Medial pathology was frequently identified in the forelimbs, and more lateral pathology was reported in the hindlimbs, which could potentially reflect differences in the loading patterns. Significant differences in MRI findings were found between different sports activities, with MCP/MTP bone pathology occurring more frequently in MRI reports from race and endurance horses and MCP/MTP soft tissue injuries being reported more frequently in dressage and show-jumping horses, particularly in the suspensory apparatus, including the distal sesamoidean ligaments. The findings of this study identify patterns of MCP/MTP abnormalities detected using standing MRI, with differences seen between forelimbs and hindlimbs and between different sports disciplines.

Influence of microarchitecture on stressed volume and mechanical fatigue behaviour of equine subchondral bone

Fractures of the equine metacarpophalangeal (MCP) joint are among the most common and fatal injuries experienced by racehorses. These bone injuries are a direct result of repetitive, high intensity loading of the skeleton during racing and training and there is consensus that they represent a mechanical fatigue phenomenon. Existing work has found the fatigue life of bone to be strongly determined by bone microarchitecture and the resulting stressed volume (i.e., the volume of bone stressed above assumed yield). The purpose of this study was to quantify the influence of bone microarchitecture on the mechanical fatigue behaviour of equine subchondral bone from the MCP joint across a wide variety of sample types. Forty-eight subchondral bone samples were prepared from the third metacarpal (MC3) and proximal phalanx (P1) of 8 horses and subsequently imaged using high resolution micro-computed tomography (μCT) to quantify microarchitectural features of interest, including bone volume fraction, tissue mineral density, pore size, pore spacing, and pore number. Samples were cyclically loaded in compression to a stress of 70 MPa, and fatigue life was defined as the number of cycles until failure. Finite element models were created from the μCT images and used to quantify stressed volume. Based on the expected log point-wise predictive density, stressed volume was a strong predictor of fatigue life in both the MC3 and P1. A regional analysis indicated fatigue life was more strongly associated with bone volume fraction in the superficial (r2 = 0.32, p < 0.001) and middle (r2 = 0.70, p < 0.001) regions of the subchondral bone, indicating the prominent role that the cortical plate played in the fatigue resistance of equine subchondral bone. By improving our understanding of the variance in fatigue life measurements, this research helps clarify the underlying mechanisms of the mechanical fatigue process and provides a basic understanding of subchondral bone injuries in the equine fetlock joint.

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.

Positron emission tomography assessment of metacarpal/metatarsal condylar fractures post surgical repair: Prospective study in 14 racehorses

OBJECTIVES

To assess 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) findings associated with metacarpal/metatarsal condylar fractures at the time of fracture repair and through healing.

STUDY DESIGN

Prospective descriptive study.

ANIMALS

Fourteen Thoroughbred racehorses.

METHODS

18F-NaF PET was performed within 4 days of surgical metacarpal/metatarsal condylar fracture repair, on both the injured and contralateral limb. Follow-up PET scans were offered at 3- and 5-months post fracture repair. Areas of abnormal uptake were assessed using a previously validated grading system.

RESULTS

Eight fractures were located in the parasagittal groove (PSG) (six lateral and two medial) and six fractures were located abaxial to the PSG (non-PSG) through the palmar/plantar condyle (all lateral). All horses in the latter group had uptake in the lateral palmar condyle of the contralateral limb suggestive of stress remodeling. Three horses with PSG fractures had uptake in a similar location in the contralateral limb. Horses with lateral condylar fracture only presented minimal or mild uptake in the medial condyle, which is considered atypical in the front limbs for horses in full training. Four horses developed periarticular uptake in the postoperative period suggestive of degenerative joint disease, three of these horses had persistent uptake at the fracture site. These four horses did not return to racing successfully.

CONCLUSION

The findings of this study provide evidence of pre-existing lesions and specific uptake patterns in racehorses suffering from metacarpal/metatarsal condylar fractures.

CLINICAL SIGNIFICANCE

PET has a possible role in the prevention, diagnosis, and postoperative monitoring of metacarpal/metatarsal condylar fractures in racehorses.

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.

Three-Dimensional Imaging and Histopathological Features of Third Metacarpal/Tarsal Parasagittal Groove and Proximal Phalanx Sagittal Groove Fissures in Thoroughbred Horses

Fissure in the third metacarpal/tarsal parasagittal groove and proximal phalanx sagittal groove is a potential prodromal pathology of fracture; therefore, early identification and characterisation of fissures using non-invasive imaging could be of clinical value. Thirty-three equine cadaver limbs underwent standing cone-beam (CB) computed tomography (CT), fan-beam (FB) CT, low-field magnetic resonance imaging (MRI), and macro/histo-pathological examination. Imaging diagnoses of fissures were compared to microscopic examination. Imaging features of fissures were described. Histopathological findings were scored and compared between locations with and without fissures on CT. Microscopic examination identified 114/291 locations with fissures. The diagnostic sensitivity and specificity were 88.5% and 61.3% for CBCT, 84.1% and 72.3% for FBCT, and 43.6% and 85.2% for MRI. Four types of imaging features of fissures were characterised on CT: (1) CBCT/FBCT hypoattenuating linear defects, (2) CBCT/FBCT striated hypoattenuated lines, (3) CBCT/FBCT subchondral irregularity, and (4) CBCT striated hypoattenuating lines and FBCT subchondral irregularity. Fissures on MRI appeared as subchondral bone hypo-/hyperintense defects. Microscopic scores of subchondral bone sclerosis, microcracks, and collapse were significantly higher in locations with CT-identified fissures. All imaging modalities were able to identify fissures. Fissures identified on CT were associated with histopathology of fatigue injuries.

Residual effects of intra-articular betamethasone and triamcinolone acetonide in an equine acute synovitis model

BACKGROUND

Intra-articular (IA) corticosteroids are regularly used in equine athletes for the control of joint inflammation.

OBJECTIVES

The goal of this study was to use an acute synovitis inflammation model to determine the residual effects of IA betamethasone and triamcinolone acetonide on various inflammatory parameters and lameness.

STUDY DESIGN

Crossover randomised trial.

METHODS

Five mixed-breed, 2-year-old horses were randomly allocated to an IA treatment of the radiocarpal joint with 9 mg of either betamethasone or triamcinolone acetonide. Two weeks following treatment, horses were injected with 1 μg of lipopolysaccharide (LPS) diluted in 1 ml of saline. Following LPS injection, horses were crossed-over and both sets of injections were repeated after a washout period. Blood samples were collected at multiple time points for mRNA analysis, as well as serum amyloid A (SAA) and cortisol determination. At each time point, lameness was also subjectively scored. Additional injections with saline-only or LPS-only (twice) were conducted as negative and positive controls, respectively. Two-way repeated measures analysis of variance was used to analyse all data.

RESULTS

Corticosteroid-only treatments result in significant mRNA expression differences, as well as significant and prolonged cortisol suppression. Following LPS injection, there was a residual treatment effect with triamcinolone evidenced by a significant treatment effect on IL-6 and PTGS1 (cyclooxygenase-1), lameness, SAA and cortisol concentrations, while only IL-6 expression was affected by betamethasone.

MAIN LIMITATIONS

The acute synovitis model used here results in significant inflammation and is not representative of the low-grade inflammation seen with typical joint disease and residual anti-inflammatory effects may be more profound in naturally occurring joint disease.

CONCLUSIONS

Current regulatory guidelines may be insufficient if the concern is residual anti-inflammatory effects. Additionally, intra-articular corticosteroid administration is not without risk, as evidenced by a significant suppression of serum cortisol concentration and, as such, the benefits of their administration should be weighed against those risks.

Relationship between CT-Derived Bone Mineral Density and UTE-MR-Derived Porosity Index in Equine Third Metacarpal and Metatarsal Bones

Fatigue-related subchondral bone injuries of the third metacarpal/metatarsal (McIII/MtIII) bones are common causes of wastage, and they are welfare concerns in racehorses. A better understanding of bone health and strength would improve animal welfare and be of benefit for the racing industry. The porosity index (PI) is an indirect measure of osseous pore size and number in bones, and it is therefore an interesting indicator of bone strength. MRI of compact bone using traditional methods, even with short echo times, fail to generate enough signal to assess bone architecture as water protons are tightly bound. Ultra-short echo time (UTE) sequences aim to increase the amount of signal detected in equine McIII/MtIII condyles. Cadaver specimens were imaged using a novel dual-echo UTE MRI technique, and PI was calculated and validated against quantitative CT-derived bone mineral density (BMD) measures. BMD and PI are inversely correlated in equine distal Mc/MtIII bone, with a weak mean r value of -0.29. There is a statistically significant difference in r values between the forelimbs and hindlimbs. Further work is needed to assess how correlation patterns behave in different areas of bone and to evaluate PI in horses with and without clinically relevant stress injuries.

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.

Novel computed tomographic analysis demonstrates differences in patterns of bone mineral content between fracture configurations in distal condylar fractures of the third metacarpal/metatarsal bones in 97 Thoroughbred racehorses

OBJECTIVE

To evaluate bone mineral content patterns between fracture configurations using novel CT image analysis.

ANIMALS

CT images from 97 Thoroughbred racehorses with third metacarpal/tarsal condyle fractures provide the case population for analysis.

PROCEDURES

Fractures were grouped by radiographic appearance. Image analysis objectively measured area of highly attenuating pixels (aHAP), areal density of highly attenuating pixels (dHAP) utilizing novel convex hull analysis, and subjective assessment of apparent attenuation intensity ranking (AAIR) for each fracture. Differences between fracture configuration groups were evaluated.

RESULTS

Analysis of dHAP identified lower-density regions of highly attenuating pixels in propagating fractures and higher-density regions of highly attenuating pixels in unicortical fractures (P = .028). Complete and incomplete configurations were almost indistinguishable in dHAP (P = 1.000). The ratio of dHAP between fractured and nonfractured condyles revealed higher density gradients between condyles in unicortical (P = .040) and incomplete (P = .031) fractures than propagating fractures.

CLINICAL RELEVANCE

Differences in patterns of bone mineral content were identified between propagating, bicortical (incomplete and complete), and unicortical fractures of third metacarpal/tarsal bone condyles. Computer-assisted geometric measurement of dHAP identified on CT images could help to assess fracture risk in equine athletes. This application may have greater relevance as standing CT screening becomes more available.

An in vitro model for discovery of osteoclast specific biomarkers towards identification of racehorses at risk for catastrophic fractures

BACKGROUND

Focal bone microcracks with osteoclast recruitment and bone lysis, may reduce fracture resistance in racehorses. As current imaging does not detect all horses at risk for fracture, the discovery of novel serum biomarkers of bone resorption or osteoclast activity could potentially address this unmet clinical need. The biology of equine osteoclasts on their natural substrate, equine bone, has never been studied in vitro and may permit identification of specific biomarkers of their activity.

OBJECTIVES

1) Establish osteoclast cultures on equine bone, 2) Measure biomarkers (tartrate resistant acid phosphatase isoform 5b (TRACP-5b) and C-terminal telopeptide of type I collagen (CTX-I)) in vitro and 3) Study the effects of inflammation.

STUDY DESIGN

In vitro experiments.

METHODS

Haematopoietic stem cells, from 5 equine sternal bone marrow aspirates, were differentiated into osteoclasts and cultured either alone or on equine bone slices, with or without pro-inflammatory stimulus (IL-1β or LPS). CTX-I and TRACP-5b were immunoassayed in the media. Osteoclast numbers and bone resorption area were assessed.

RESULTS

TRACP-5b increased over time without bone (p < 0.0001) and correlated with osteoclast number (r = 0.63, p < 0.001). CTX-I and TRACP-5b increased with time for cultures with bone (p = 0.002; p = 0.02 respectively), correlated with each other (r = 0.64, p < 0.002) and correlated with bone resorption (r = 0.85, p < 0.001; r = 0.82, p < 0.001 respectively). Inflammation had no measurable effects.

MAIN LIMITATIONS

Specimen numbers limited.

CONCLUSIONS

Equine osteoclasts were successfully cultured on equine bone slices and their bone resorption quantified. TRACP-5b was shown to be a biomarker of equine osteoclast number and bone resorption for the first time; CTX-I was also confirmed to be a biomarker of equine bone resorption in vitro. This robust equine specific in vitro assay will help the study of osteoclast biology.

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.

Computed tomographic assessment of fracture characteristics and subchondral bone injury in Thoroughbred racehorses with lateral condylar fractures and their relationship to outcome

OBJECTIVE

To investigate the effects of fracture characteristics and concurrent subchondral bone pathology identified with computed tomography (CT) on the racing performance of Thoroughbred racehorses with fractures of the MC3/MT3 lateral condyle.

STUDY DESIGN

Retrospective cohort study.

SAMPLE POPULATION

Thoroughbred racehorses (n = 50) with a fracture of the MC3/MT3 lateral condyle, which had preoperative CT and internal fixation performed.

METHODS

Medical records were reviewed for age, sex, limb, and surgical treatment. Computed tomography scans were evaluated to determine fracture characteristics including length, whether the fracture was incomplete or complete, and displacement. The presence of subchondral bone injury (SBI), sesamoid bone fracture, articular comminution, and fragmentation in the joint was noted. Racing data was obtained from an online database. Univariable and multivariable analyses determined associations between independent variables and outcomes.

RESULTS

Thirty-three (66%) horses raced after surgery. Horses with sesamoid bone fractures (P = .021), MC3/MT3 comminution (P = .016) and intra-articular fragmentation (P = .015) were less likely to race postoperatively. Concurrent SBI did not affect outcome. In the final multivariable model, sex (P = .015) and whether a fracture was incomplete or complete (P = .007) were the most significant predictors of racing postoperatively with females and horses with complete fractures being less likely to race.

CONCLUSION

The prognosis for racing after a lateral condylar fracture is favorable but is decreased in horses with complete fractures and certain concurrent joint pathology.

CLINICAL SIGNIFICANCE

Horses presenting with lateral condylar fractures commonly have concurrent joint pathology. Computed tomography can aid in preoperative evaluation and prognostication by enabling more complete fracture assessment.

Race-Level Reporting of Incidents during Two Seasons (2015/16 to 2016/17) of Harness Racing in New Zealand

The objective of this study was to describe the incident and non-incident reporting of harness racing in New Zealand, the primary injury and reporting outcomes, and to examine horse- and race-level variables associated with the odds of these outcomes. Retrospective stipendiary stewards’ reports of race day events during the 2015/16 to 2016/17 racing seasons were examined. The number of incident and non-incident events and binomial exact 95% confidence intervals (CI) were calculated per 1000 horse starts. Most reports were for non-incidents and an examination was requested for poor performance (11.06 per 1000 starts (95% CI = 10.23–11.89). Races with more than eight participants were 1.9 (95% CI = 1.13–3.4) times more likely to have an incident than races with eight or less participants. The low incidence of significant injuries such as fractures (0.13 per 1000 starts (95% CI = 0.03–0.23) reflects the lower risk of injury in harness racing compared to Thoroughbred racing. The high incidence of poor performance reports highlights the steward’s role in maintaining animal welfare to a high standard.

Imaging and Gross Pathological Appearance of Changes in the Parasagittal Grooves of Thoroughbred Racehorses

Simple Summary

Early detection of racehorses at risk of stress fracture is key to reducing the number of horses with catastrophic fractures while racing. Bone changes are often visible in the limbs of Thoroughbred racehorses in work, particularly in the fetlock region. However, it is currently unknown whether some of these changes indicate an impending fracture or are a healthy adaptation to high-speed exercise. This study looks at imaging and gross changes in a specific area (parasagittal grooves (PSGs) of the cannon bone) and the utility of X-ray, computed tomography (CT) and magnetic resonance imaging (MRI) to detect the changes. All fetlock joints were assessed from twenty horses that died during racing or training, including horses with and without fetlock fracture. Overall, X-ray was poor for detecting PSG changes. Some PSG changes on CT and MRI were common in Thoroughbred racehorses and possibly represent normal bone adaptation when seen in clinical cases. However, certain CT and MRI findings were more prevalent in horses with a fracture, possibly indicating microdamage accumulation and increased risk of fracture. Bilateral advanced imaging is recommended in clinical cases of suspected fetlock pathology.

Abstract

(1) Background: Parasagittal groove (PSG) changes are often present on advanced imaging of racing Thoroughbred fetlocks and have been suggested to indicate increased fracture risk. Currently, there is limited evidence differentiating the imaging appearance of prodromal changes in horses at risk of fracture from horses with normal adaptive modelling in response to galloping. This study aims to investigate imaging and gross PSG findings in racing Thoroughbreds and the comparative utility of different imaging modalities to detect PSG changes. (2) Methods: Cadaver limbs were collected from twenty deceased racing/training Thoroughbreds. All fetlocks of each horse were examined with radiography, low-field magnetic resonance imaging (MRI), computed tomography (CT), contrast arthrography and gross pathology. (3) Results: Horses with fetlock fracture were more likely to have lateromedial PSG sclerosis asymmetry and/or lateral PSG lysis. PSG lysis was not readily detected using MRI. PSG subchondral bone defects were difficult to differentiate from cartilage defects on MRI and were not associated with fractures. The clinical relevance of PSG STIR hyperintensity remains unclear. Overall, radiography was poor for detecting PSG changes. (4) Conclusions: Some PSG changes in Thoroughbred racehorses are common; however, certain findings are more prevalent in horses with fractures, possibly indicating microdamage accumulation. Bilateral advanced imaging is recommended in racehorses with suspected fetlock pathology.

Cartilage Degeneration of the Metacarpal Condyle and Enthesopaties of The Collateral Ligaments of Equine Metacarpophalangeal Joint

Articular degeneration can be characterized by fibrillation and eburnation of the articular layers of the metacarpophalangeal (MP) joint. Structural changes within the articular joint predispose the development of osteophytes, enthesophytes and, in many cases is associated with changes the collateral ligaments of the MP joint. The aim of the present study was to investigate the relationship between degenerative processes of the articular cartilage and the enthesopathies of collateral ligaments (superficial or deep portion) of the equine MP joint, using radiographic, ultrasonographic and anatomopathological exam, as well as establishing their sensitivity. Thirty equine forelimbs were selected from animals that died due to various clinical conditions with an average age of 5.7 years which came from a private clinic or sent to the Laboratory of Veterinary Pathology of UFSM. The specimens were placed in a hydraulic press and submitted to radiographic evaluation of the MP joint (lateromedial, flexed lateromedial, dorsopalmar, dorsolateral-palmaromedial oblique 45⁰ and dorsomedial-palmarolateral oblique 45⁰ projections). Transversal and longitudinal ultrasound images of the dorsal and collateral aspect of the MP joint were obtained using a Sonosite Edge machine with a 5 to 10 MHz linear transducer. Subsequently, the specimens were sent for gross and histopathological examination. A highly positive correlation (P value <.001) was observed between ultrasonographic and macroscopic techniques, showing a relationship between the cartilaginous degenerations of the MP joint and the medial and lateral LC enthesopathies.

Comparative evaluation of tomosynthesis, computed tomography, and magnetic resonance imaging findings for metacarpophalangeal joints from equine cadavers

OBJECTIVE

To describe the technique and assess the diagnostic potential and limitations of tomosynthesis for imaging of the metacarpophalangeal joint (MCPJ) of equine cadavers; compare the tomosynthesis appearance of pathological lesions with their conventional radiographic, CT, and MRI appearances; and evaluate all imaging findings with gross lesions of a given MCPJ.

SAMPLE

Distal portions of 4 forelimbs from 4 equine cadavers.

PROCEDURES

The MCPJs underwent radiography, tomosynthesis (with a purpose-built benchtop unit), CT, and MRI; thereafter, MCPJs were disarticulated and evaluated for the presence of gross lesions. The ability to identify pathological lesions on all images was assessed, followed by semiobjective scoring for quality of the overall image and appearance of the subchondral bone, articular cartilage, periarticular margins, and adjacent trabecular bone of the third metacarpal bone, proximal phalanx, and proximal sesamoid bones of each MCPJ.

RESULTS

Some pathological lesions in the subchondral bone of the third metacarpal bone were detectable with tomosynthesis but not with radiography. Overall, tomosynthesis was comparable to radiography, but volumetric imaging modalities were superior to tomosynthesis and radiography for imaging of subchondral bone, articular cartilage, periarticular margins, and adjacent bone.

CONCLUSIONS AND CLINICAL RELEVANCE

With regard to the diagnostic characterization of equine MCPJs, tomosynthesis may be more accurate than radiography for identification of lesions within subchondral bone because, in part, of its ability to reduce superimposition of regional anatomic features. Tomosynthesis may be useful as an adjunctive imaging technique, highlighting subtle lesions within bone, compared with standard radiographic findings.

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.

A Comparative Review of Autologous Conditioned Serum and Autologous Protein Solution for Treatment of Osteoarthritis in Horses

Many alternative treatments aimed at modulating osteoarthritis (OA) progression have been developed in the past decades, including the use of cytokine inhibitors. IL-1β is considered one of the most impactful cytokines in OA disease and therefore, its blockage offers a promising approach for the modulation of OA. Interleukin-1 receptor antagonist (IL-1Ra) is a naturally occurring anti-inflammatory protein belonging to the IL-1 family that competes with IL-1β for occupancy of its receptors, without triggering the same downstream inflammatory response. Because of its natural anti-inflammatory properties, different methods have been proposed to use IL-1Ra therapeutically in OA. Autologous conditioned serum (ACS) and autologous protein solution (APS) are blood-derived products produced with the use of specialized commercial kits. These processes result in hemoderivatives with high concentrations of IL-1Ra and other cytokines and growth factors with potential modulatory effects on OA progression. Several studies have demonstrated potential anti-inflammatory effect of these therapies with promising clinical results. However, as with any hemoderivatives, clinical outcomes may vary. For optimal therapeutic use, further research is warranted for a more comprehensive understanding of the product's composition and interaction of its components in joint inflammation. Additionally, differences between ACS and APS treatments may not be clear for many clients and clinicians. Thus, the objective of this narrative review is to guide the reader in important aspects of ACS and APS therapies, in vitro and in vivo applications and to compare the use of both treatments in OA.

Expression of select mRNA in Thoroughbreds with catastrophic racing injuries

BACKGROUND

The ability to identify horses at risk for catastrophic injuries continues to be a pressing issue for the racing industry, especially given recent events in North America.

OBJECTIVES

Since most catastrophic injuries occur in areas of existing pathology and this pathology is likely to elicit an inflammatory response, it was hypothesised that analysis of messenger RNA (mRNA) expression would detect significant changes in select genes in horses at risk for a catastrophic injury.

STUDY DESIGN

Prospective cohort study.

METHODS

Five racing jurisdictions across the United States participated in this study. A total of 686 Tempus^® RNA Blood Tube samples were collected for mRNA analysis from 107 catastrophically injured horses, as well as from noninjured horses sampled either prerace (n = 374) or postrace (n = 205). A subset of horses (n = 37) were sampled both prerace and postrace for analysis of expression changes during the postrace period.

RESULTS

Of 21 genes analysed via RT-qPCR, the expression of 12 genes (ALOX5AP, CD14, IL-10, IL-1β, IL-6, IL-8, MMP1, PTGS2, TLR4, TNFα, TNFSF13B and VEGFA) changed significantly within 45 minutes after a race and were excluded. Of the remaining nine genes (BMP-2, IGF-1, IL1RN, MMP2, MMP9, Osteoprotegrin, RANKL, SAA1 and TGFβ), three genes (IGF-1, IL1RN and MMP2) were found to be significantly different between catastrophically injured and noninjured horses using multiple logistic regression modelling. Receiver operating characteristic analysis of models, which included mRNA expression, demonstrated sensitivities from 76%-82% (95% CI: 67%-93%) and specificities from 84%-88% (95% CI: 71%-94%) at the Youden Index.

MAIN LIMITATIONS

Samples were collected as soon as possible postinjury (within 30 minutes).

CONCLUSIONS

Analysis of mRNA expression of specific genes in the future may be considered as an economical, accessible and noninvasive means by which horses at risk for catastrophic injury can be identified.

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.

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.

Subchondral focal osteopenia associated with proximal sesamoid bone fracture in Thoroughbred racehorses

BACKGROUND

Proximal sesamoid bone (PSB) fracture is the most common fatal injury in Thoroughbred (TB) racehorses in the United States. Epidemiological and pathological evidence indicates PSB fracture is likely the acute culmination of a chronic stress-related process. However, the aetiopathogenesis of PSB fracture is poorly understood.

OBJECTIVE

To characterise bone abnormalities that precede PSB fracture.

STUDY DESIGN

Two retrospective case-control groups of PSBs from TB racehorses with, and without, unilateral biaxial PSB fracture.

METHODS

Proximal sesamoid bones were harvested post-mortem from TB racehorses subjected to euthanasia for unilateral biaxial PSB fracture (cases) or causes unrelated to PSB fracture (controls) while racing or training. The fractured medial PSB (FX-PSB) and contralateral intact medial PSB (CLI-PSB) from racehorses that sustained PSB fracture, and an intact medial PSB (CTRL-PSB) from racehorses that did not have a PSB fracture were collected as case and control specimens. Study 1 distributions of morphological features were compared among case and control groups using visual examination, photographs, radiographs and histology of whole PSBs and serial sagittal sections (10 FX-PSB, 10 CLI-PSB and 10 CTRL-PSB). Study 2 local bone volume fraction and mineral densities were compared among case and control PSBs using microcomputed tomography (9 FX-PSB, 9 CLI-PSB and 9 CTRL-PSB).

RESULTS

A focal subchondral lesion characterised by colocalised focal discoloration, radiolucency, osteopenia, low tissue mineral density and a surrounding region of dense cancellous bone was identified in most case horses but not in controls. This subchondral lesion was found in a slightly abaxial mid-body location and was bilaterally present in most case horses.

MAIN LIMITATIONS

The post-mortem samples may not represent the spectrum of abnormalities that occur throughout the development of the subchondral lesion. Lateral PSBs were not examined, so their contribution to biaxial PSB fracture pathogenesis is unknown.

CONCLUSION

Abaxial subchondral lesions are consistent with pre-existing injury and likely associated with PSB fracture.

Undenatured Type II Collagen (UC-II) in Joint Health and Disease: A Review on the Current Knowledge of Companion Animals

OA is quite common in companion animals, especially in large breed dogs and horses. Collagen, the most abundant protein of mammals, has specific connective tissue types for skin, bones, reticulate, basal lamina, bones, cell surfaces, while type II collagen (UC-II) forms the main structure of cartilage tissue. Even at the smaller dosages, UC-II has also been reported to be more effective than the glucosamine and chondroitin sulfate supplements, which are the supplements most frequently used in the market. In this review, we summarize the effects of UC-II on joint health and function in health and disease conditions in companion animals.

Abundant osteoclasts in the subchondral bone of the juvenile Thoroughbred metacarpus suggest an important role in joint maturation

BACKGROUND

The administration of bisphosphonate medications, which target osteoclastic-bone remodelling, to juvenile and adult racehorses is a matter of debate owing to concerns that these molecules remain bound to the bone-mineralised matrix and may interfere with subsequent bone growth, adaptation to exercise and healing of bone microdamage in equine athletes. Osteoclasts participate in endochondral ossification, subchondral bone remodelling and bone repair. There is a knowledge gap on the role of equine osteoclast biology in the growth and maturation of joint surfaces and this information is important to inform judicious bisphosphonate use.

OBJECTIVES

Measure and compare the osteoclast density in the subchondral bone of Thoroughbred (TB) distal third metacarpi (McIII) at different sites, varying depths from the articular surface and with age (0-84 months).

STUDY DESIGN

Ex vivo cadaveric study.

METHODS

McIIIs from foals, yearlings and adults were collected, fixed in formaldehyde and stored at 4°C. Sections were cut from the lateral hemi-metacarpus, stained and scored for cartilage degeneration. Osteoclasts were counted on immunohistochemically (Cathepsin K) stained sections. Osteoclast density was compared in regions of interest (ROIs-the sagittal ridge, axial and abaxial condyle) and also at two depths (0-3 mm and 3-6 mm) into the subchondral bone below the osteochondral junction.

RESULTS

The osteoclast density was consistently highest in the subchondral cortical bone plate (0-3 mm) when compared with the deeper trabecular bone in all age groups. Furthermore, the osteoclast density was significantly higher in juvenile Thoroughbreds (foals and yearlings) within both sites in the subchondral bone when compared with adults.

MAIN LIMITATIONS

The number of specimens available for study was restricted.

CONCLUSIONS

Osteoclasts are important in normal McIII epiphyseal and articular surface maturation and have a propensity to localise at the osteochondral junction and subchondral cortical bone plate zone in juvenile Thoroughbreds.

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.

Warmblood fragile foal syndrome type 1 mutation (PLOD1 c.2032G>A) is not associated with catastrophic breakdown and has a low allele frequency in the Thoroughbred breed

Background

Catastrophic fractures are among the most common cause of fatalities in racehorses. Several factors, including genetics, likely contribute to increased risk for fatal injuries. A variant in the procollagen‐lysine, 2‐oxoglutarate 5‐dioxygenase1 gene (PLOD1 c.2032G>A) was shown to cause Warmblood fragile foal syndrome type 1 (WFFS), a fatal recessive defect of the connective tissue. Screening of multiple horse breeds identified the presence of the WFFS allele in the Thoroughbred. PLOD1 is involved in cross‐linking of collagen fibrils and thus could potentially increase the risk of catastrophic breakdown.

Objectives

Estimate the frequency of the WFFS allele (PLOD1 c.2032G>A) and determine if it is a risk factor for catastrophic breakdown in the Thoroughbred.

Study design

Case–control genetic study.

Methods

Genomic DNA from hair and/or tissue samples was genotyped for the WFFS allele. Fisher’s Exact tests were performed to compare allele and carrier frequencies between the case cohort (catastrophic breakdown, n = 22) and several cohorts with no record of injury (n = 138 raced/trained at same track and season and n = 185 older than 7 years and raced during same season), nonracers (n = 92), and a random sample without consideration for racing history (n = 279).

Results

The frequency of the PLOD1 c.2032G>A variant in the Thoroughbred breed is low (1.2%). Seventeen of 716 Thoroughbreds tested were carriers (2.4%) and no WFFS homozygotes were detected. Only one catastrophic breakdown case carried the WFFS allele. No statistically significant difference in allele or carrier frequency was identified between case and control cohorts (P>0.05 in all comparisons performed).

Main limitations

This study evaluated cases from one single track.

Conclusions

This study demonstrated that the PLOD1 c.2032G>A associated with WFFS is present at very low frequency in Thoroughbreds and is not a genetic risk factor for catastrophic breakdown.

A method for fatigue testing of equine McIII subchondral bone under a simulated fast workout training programme

BACKGROUND

Standard fatigue testing of bone uses a single load and frequency applied until failure. However, in situ, the subchondral bone of Thoroughbred racehorses is subjected to a combination (or a spectrum) of loads and frequencies during training and racing.

OBJECTIVE

To investigate the use of a fatigue testing method for equine third metacarpal (McIII) subchondral bone under a spectrum of loading conditions which a racehorse is likely to experience during a fast workout.

STUDY DESIGN

In vitro biomechanical experimental study.

METHODS

McIII subchondral bone specimens (n = 12) of racehorses were harvested from left and right medial condyles. A novel fatigue loading protocol was developed based upon a standard sequence of gaits during a typical fast workout protocol. This loading pattern, or loading loop, was repeated until the failure of the specimen.

RESULTS

The mean ± standard deviation for all specimens for total time-to-failure was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 fast workouts). Ten of twelve specimens withstood at least one complete loop equivalent to a fast workout. All specimens failed during simulated gallop loading.

MAIN LIMITATIONS

The resting time between loops was much shorter than in vivo resting time and specimens were unconfined during compressive testing.

CONCLUSIONS

This novel fatigue loading protocol more closely mimics in vivo fatigue loading of McIII subchondral bone and demonstrates the importance of the highest speeds in the development of subchondral bone injury.

Bone marrow oedema-type signal in the proximal phalanx of Thoroughbred racehorses

This study focused on 8 Thoroughbred racehorses showing bone marrow oedema-type signal in the proximal sagittal groove of the proximal phalanx, with the aim of understanding its clinical significance. Standing magnetic resonance imaging played an important role in assessing osseous abnormalities that were not radiographically identifiable. Further, a histopathological result from one of the cases showed there was oedema surrounding adipose tissues with increase in density of trabecular scaffolding. This may indicate presence of osseous injury within the area of decreased elasticity due to subchondral bone modeling. This study suggests that detection of osseous abnormality based on bone marrow oedema-type signal, and application of appropriate care following injury would contribute to prevent deterioration of stress-related fractures of the proximal phalanx.

A Thoroughbred racehorse with a unicortical palmar lateral condylar fracture returned to training 14 days after surgery: a hypothesis on the role of a single bone screw on crack propagation

A 2-year-old Thoroughbred racehorse had LF lameness that began post high-speed exercise and persisted for two days before the horse once again became sound. Diagnostic analgesia localized the lameness to the LF distal metacarpus, and a standing MRI identified a unicortical condylar fracture. A single 5.5 mm cortical screw was placed in lag fashion. The horse began hand walking at 14 days, racetrack jogging at 30 days, and racing at 5 months after the day of surgery. Placement of a single lag screw ahead of the tip of the crack in unicortical condylar fracture may be useful for reducing the recovery period for horses returning to training and racing.

Subchondral bone microdamage accumulation in distal metacarpus of Thoroughbred racehorses

BACKGROUND

Microdamage accumulation leads to subchondral bone injury and/or fracture in racehorses. An understanding of this process is essential for developing strategies for injury prevention.

OBJECTIVES

To quantify subchondral bone microdamage in the third metacarpal bone of Thoroughbred racehorses at different stages of the training cycle.

STUDY DESIGN

Cross-sectional.

METHODS

Bone blocks from the palmar aspect of the medial condyles of third metacarpal bones from 46 racing Thoroughbred horses undergoing post-mortem were examined with micro computed tomography (microCT) to detect calcified microcracks, and light microscopy to quantify bulk stained microcracks. Racing and training histories were obtained for comparison with microdamage data using regression modelling.

RESULTS

Subchondral bone microcracks were observed in all bones with at least one method. Microdamage grade was greater in older horses, levelling-off for horses 5 years and older (quadratic term P = 0.01), and with lower bone material density in the parasagittal groove (P = 0.02). Microcrack density was higher in older horses (P = 0.004), and with higher bone volume fraction (BV/TV) in the parasagittal groove in horses in training (interaction effect, P = 0.01) and lower in horses resting from training (P = 0.02).

MAIN LIMITATIONS

Cross-sectional data only. Incomplete detection of microdamage due to the limits of resolution of microCT and lack of three-dimensional imaging with microscopy. Multicollinearity between variables that indicated career progression (e.g. age, number of career starts, duration of training period) was detected.

CONCLUSIONS

Fatigue damage in the distal metacarpal subchondral bone is common in Thoroughbred racehorses undergoing post-mortem and appears to accumulate throughout a racing career. Reduced intensity or duration of training and racing and/or increased duration of rest periods may limit microdamage accumulation. Focal subchondral bone sclerosis indicates the presence of microdamage.

Epidemiology of fractures: The role of kick injuries in equine fractures

BACKGROUND

Fractures occur commonly in equids and often are associated with complications and a poor outcome. There are no reports on the epidemiology of fractures in a heterogeneous equine population.

OBJECTIVES

To study the epidemiology of fractures in a heterogeneous equine population, focusing on differences between fractures resulting from a kick and fractures, resulting from other causes and investigating predictors for recovery.

STUDY DESIGN

Retrospective case series.

METHODS

Data of all equids presented to the Equine Department, Vetsuisse Faculty, University of Zurich between 1990 and 2014 and diagnosed with a fracture were reviewed and those with a known cause were included in this study. Mann-Whitney and chi-squared tests were used to compare recovery rates of fractures resulting from a kick and fractures resulting from other causes, and a logistic regression was carried out for multivariate analysis of the most important factors affecting recovery.

RESULTS

Here, 1144 cases fulfilled the inclusion criteria. Of all fractures (with a known cause), 43.6% were the result of a kick from another equid. Kicks often produced open fractures (44.7%) that involved bones of the limbs (85.6%). Overall recovery was 70.1%. Logistic regression showed that high-grade lameness accompanying the fracture and severe comminution negatively affected recovery.

MAIN LIMITATIONS

The equids in this study were drawn from a referred population, which likely precluded the inclusion of both minor fractures and catastrophic fractures that necessitated immediate euthanasia. Moreover, many cases were excluded because the cause of the fracture could not be determined from the patient record.

CONCLUSIONS

Kicks are the most common cause of fractures in a heterogeneous equine population and measures to reduce the incidence of kicks are necessary in group-housing systems.

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.