A systematic literature search to identify performance measure outcomes used in clinical studies of racehorses

Cardiovascular Fitness and Stride Acceleration in Race-Pace Workouts for the Prediction of Performance in Thoroughbreds

In-training racehorse physiological data can be leveraged to further explore race-day performance prediction. To date, no large retrospective, observational study has analysed whether in-training speed and heart rate recovery can predict racehorse success. Speed (categorised as 'slow' to 'fast' according to the time taken to cover the last 600 m from a virtual finish line) and heart rate recovery (from gallop to 1 min after exercise) of flat racehorses (n = 485) of varying age, sex and type according to distance (e.g., sprinter, miler and stayer) were obtained using a fitness tracker from a single racing yard in Australia. Race-pace training sessions on turf comprised 'fast gallop' (n = 3418 sessions) or 'jumpout' (n = 1419). A posteriori racing information (n = 3810 races) for all 485 racehorses was extracted and combined with training data. Race performance was categorised as win/not-win or podium or not, each analysed by logistic regression. Colts (p < 0.001), stayers (p < 0.001) and being relatively fast over the last 600 m of a benchmark test in training (p < 0.008) were all predictive of race performance. Heart rate recovery after exercise (p = 0.21) and speed recorded at 600 m of a 1 km benchmark test in training (p = 0.94) were not predictive. In-training physiological data analytics used along with subjective experience may help trainers identify promising horses and improve decision-making.

Equine subchondral lucencies: Knowledge from the medial femoral condyle

Equine subchondral lucencies (SCL) have been described since the first availability of suitable radiographic equipment. The initial clinical sign can be lameness, but SCLs are often first found on surveys of juvenile horses and are primarily a radiographic concern for public auctions. When lameness is present, it varies from subtle to obvious and can be intermittent. Some SCLs heal spontaneously, and some remain blemishes, but when the SCL and lameness are persistent, further damage to the joint and limitations to an athletic career are likely. SCLs were initially described in the distal limb followed by the stifle, and the medial femoral condyle (MFC) is now considered the most common location. The aim of this review is to highlight the initial pathology and discuss the clinical and experimental information available on equine SCLs. SCL treatment has evolved from rest alone and has progressed to debridement, grafting, intralesional injection, and most recently, transcondylar screw and absorbable implant placement. Comparison of success rates between techniques is difficult due to variations in follow-up and outcome measures, and no single technique is best for all SCLs. Treatment appears to increase success by 15%-20% over rest alone, but the method chosen depends on many factors. This review emphasizes the need for further work to fully understand SCL formation and all aspects of trabecular bone healing to optimize surgical therapy and improve treatment success.

Subchondral lucencies of the medial femoral condyle in yearling and 2-year-old Thoroughbred sales horses: Prevalence, progression and associations with racing performance

BACKGROUND

Subchondral lucencies (SCLs) in the distal aspect of the medial femoral condyle (MFC) of young Thoroughbred horses are a source of controversy on presale radiographs. There is limited scientific evidence regarding the risk of progression and impact on future racing performance.

OBJECTIVES

To (1) identify the prevalence of MFC SCLs on sales repository radiographs in yearling and 2-year-old Thoroughbreds; (2) identify any association between grade of MFC SCL and future racing performance and (3) monitor changes in MFC SCL grades between yearling and 2-year-old sales.

STUDY DESIGN

Prospective cohort study.

METHODS

Radiographs were obtained with consignor permission from a 2016 yearling sale and five 2017 2-year-old sales. Stifle radiographs were evaluated and MFC SCLs graded on a scale of 0-3. Axial MFC lucencies were recorded separately. Maximum MFC grades per horse were analysed for associations with racing performance outcomes, adjusted for sex, to the end of the horses' 4-year-old racing year. Analysis was via logistic, negative binomial or linear regression as appropriate, with the threshold for significance set at α = 0.05.

RESULTS

Radiographs from 2508 yearlings (5016 stifles) and 436 2-year-olds (872 stifles) were included in the study. MFC SCLs of grades 1-3 were observed in 242 (9.65%) yearlings and 49 (11.2%) 2-year-olds. Bilateral MFC SCLs of grades 1-3 were observed in 54 (2.2%) yearlings and 12 (2.8%) 2-year-olds. Grade 1 MFC SCLs in yearlings either remained unchanged (14/31), progressed to a grade 2 (6/31) or resolved (11/31) by the 2-year-old sale. Grade 2 MFC SCLs in yearlings remained unchanged (6/10), progressed to a grade 3 (2/10) or improved to a grade 1 (2/10). Yearlings with a grade 3 MFC SCL had a 78% probability of starting a race (95% confidence interval [CI] 58.2-89.6%), compared with an 84% probability of racing for grade 0 yearlings (95% CI 82.7-85.8%). Six of the seven yearlings with axial MFC lucencies raced.

MAIN LIMITATIONS

This study may underestimate the prevalence of severe lesions in the general yearling population of U.S. Thoroughbreds. However, the convenience sample used is representative of the population of interest at sales. The study design could not address exclusions prior to sale.

CONCLUSIONS

Grade 1 MFC SCLs are the most common type seen in yearling and 2-year-old sales horses. The majority of yearling grade 1 MFC SCLs resolved or remained static by 2-year-old sales. It was also possible for grade 2 and 3 MFC SCLs to improve one grade between sales. Fewer sales yearlings with a grade 3 MFC SCL raced, but in those that did race there was no evidence of worse performance compared to unaffected peers. Axial MFC lucencies did not affect racing performance.

A cross-sectional study of colic and rate of return to racing in Thoroughbreds at Seoul Racecourse in Korea between 2010 and 2020

BACKGROUND

The incidence of colic and the outcomes of colic surgery have not been surveyed in racetracks in Korea.

OBJECTIVES

This study examined the incidence, mortality, and case fatality of colic and investigated the effects of age and sex after an exploratory celiotomy on the long-term survival rate (return to racing), subsequent racing performance, and career longevity.

METHODS

The incidence, mortality, and case fatalities of colic were examined over an 11-year period. The records of 40 horses that had undergone a celiotomy, after participating in at least one race and 75 race-matched control horses were analyzed. The racing performance and career length of the horses that returned to racing post-surgery were compared with a control group.

RESULTS

The annual incidence, fatality rate of colic, and annual mortality rate at Seoul Racecourse were 6.5, 2.8 per 100 horse-years, and 0.2 deaths cases per 100 horse-years, respectively. Of the 40 horses that underwent colic surgery, 26 (65%) returned to racing. The likelihood of returning to racing decreased with increasing age of the horses, and geldings had a lower probability of returning. While the performance in the five preoperative races between the two groups was not significantly different, a significant decrease in racing performance was observed after the surgery date (p < 0.01). Horses that underwent colic surgery did not show a significant decrease in career length.

CONCLUSIONS

Surgical treatment for colic at the age of three and four years had a negative impact on the racing performance. On the other hand, there was no significant difference in career longevity between the two groups.

Evaluation of fitness parameters in relation to racing results in 245 Standardbred trotter horses submitted for poor performance examination: A retrospective study

In racehorses, the associations between physiological parameters obtained by exercise testing and racing results have been questioned. We hypothesized that fitness variables measured during a treadmill incremental test may be related with racing outcomes and lifetime career. Our study aimed to investigate the role of fitness parameters obtained during a treadmill test in performance evaluation and career prediction in poorly performing Standardbreds, through a retrospective review of the clinical records of 245 trotters that underwent an incremental treadmill test. Several fitness parameters were assessed, and their correlations with racing data (number of starts, wins and placings) in the 3 months before and 6 months after examination were evaluated; moreover their associations and predictive power for lifetime racing results and earnings were considered. The associations between fitness parameters and measures of racing performance as well as the associations between racing results over time were evaluated by Spearman's correlation in the whole population and in different age groups. Multivariate regression models predicting the total number of starts, wins and earnings based on fitness parameters were constructed, controlling for age, weight, and sex. Maximum speed and the speed at the aerobic threshold were the parameters correlated with the most racing results, in the three evaluation periods (3 months before, 6 months after, lifetime). Other parameters predictive of career outcomes were maximum blood lactate concentration and maximum hematocrit. Interestingly, in 2-year-old Standardbreds, the only parameters correlated with racing results were maximum hematocrit and minimum pH, suggesting they may reflect individual potential. Both the racing results obtained before and after examination were predictive of lifetime career, with those following hospitalization being more strongly correlated. In conclusion, parameters obtained during treadmill tests both reflect the racing outcomes and the career potential.

Treatments and Prognosis for Subchondral Cystic Lesions in the Distal Extremities in Thoroughbred Prospect Racehorses

Subchondral cystic lesions (SCLs) in equines and their treatments have been mainly studied in the medial femoral condyle of the femur. SCLs in the distal extremities affecting the fetlock or interphalangeal joints are frequent, but treatment or prognosis studies in horses are currently sparse. Our objective was to compare four treatments for SCLs in the distal extremities (intralesional injection of corticosteroids, transcortical drilling, cortical screw placement, and absorbable hydroxyapatite implant placement) and report the racing prognoses for affected thoroughbred yearlings. Data from 113 thoroughbred yearlings treated for SCLs in the distal extremities were collected from 2014 to 2020. Age at surgery, sex, bone affected, radiographic SCL measurements, SCL shape, and type of treatment were recorded. Sale data and racing performance were collected for the operated horses and for 109 maternal siblings that were free of SCLs. An analysis was conducted to assess if SCL size affected racing prognosis and to detect differences in sale value and selected racing parameters between the cases and controls. The outcomes for the different treatments, the different bones affected, and the SCL shape type were also analyzed. There was no difference in the ability to start in a race between the cases and controls (60.2% vs. 69.7%, respectively). The auction value of the treated horses was significantly lower than that of their siblings. The bone affected did not impact any of the racing variables studied, whereas the height of the SCLs negatively affected the number of wins and placed races. The type of treatment for the horses affected by SCLs did not have an impact on sale prices, ability to start a race, race starts, wins, and places, or age at the time of the first start. In conclusion, yearlings diagnosed with an SCL in the distal extremities had lower auction prices and decreased racing performances, with lower numbers of wins correlated with larger SCL heights compared to the siblings. Similar racing performance was found regardless of the treatment received.

Associations between Medical Disorders and Racing Outcomes in Poorly Performing Standardbred Trotter Racehorses: A Retrospective Study

Poor performance in racehorses is commonly associated with subclinical diseases. This study aims to evaluate the associations between medical disorders and racing results in Standardbred trotters. The clinical records of 248 poorly performing Standardbreds were retrospectively reviewed, and their racing results were extracted from an online database, concerning the periods 3 months before and 6 months after hospitalization and the entire lifetime. Generalized linear models were used to evaluate the effects of different disorders on racing outcomes. Airway neutrophilia was associated with limiting lifetime starts and wins pre- and post-hospitalization, while mastocytosis was associated with less wins in the post-hospitalization period. Therefore, lower airway inflammation showed both short- and long-term impacts on racing performance. Severe upper airway obstructions and gastric ulcers showed associations with less placings in the post-discharge period but no long-term influence on performance. The significance of exertional rhabdomyolysis was indeterminable, yet interference with the number of starts in the post-discharge period was reported and associated with lower total career earnings. Exercise-induced pulmonary hemorrhage and cardiac arrhythmias were not associated with worse racing outcomes: therefore, their role in poor performance remains unclear.

Medical causes of poor performance and their associations with fitness in Standardbred racehorses

BACKGROUND

Poor performance is a multifactorial syndrome of racehorses, commonly associated with subclinical disorders, which can be diagnosed by exercise testing.

OBJECTIVES

Describe the prevalence of medical causes of poor performance in Standardbreds unassociated with lameness, and evaluate their relationships with fitness variables measured by exercise treadmill test.

ANIMALS

Hospital population of 259 nonlame Standardbred trotters referred for poor performance.

METHODS

The horses' medical records were retrospectively reviewed. Horses underwent a diagnostic protocol including resting examination, plasma lactate concentration, treadmill test with continuous ECG and assessment of fitness variables, creatine kinase activity, treadmill endoscopy, postexercise tracheobronchoscopy, bronchoalveolar lavage (BAL), and gastroscopy. The prevalence of different disorders was evaluated, including cardiac arrhythmias, exertional myopathies, dynamic upper airway obstructions (DUAOs), exercise-induced pulmonary hemorrhage (EIPH), moderate equine asthma (MEA), and gastric ulcers (EGUS). The associations of these disorders with fitness variables were investigated individually and using multivariable models.

RESULTS

Moderate equine asthma and EGUS were the most common disorders, followed by EIPH, DUAOs, cardiac arrhythmias, and exertional myopathies. Hemosiderin score was positively correlated with BAL neutrophils, eosinophils, and mast cells; increased creatine kinase activity was associated with BAL neutrophilia, DUAOs, premature complexes, and squamous gastric disease. Treadmill velocity at a plasma lactate concentration of 4 mmol/L and at heart rate of 200 beats per minute was negatively affected by BAL neutrophilia, multiple DUAOs, exertional myopathies, and squamous gastric disease.

CONCLUSIONS

The multifactorial nature of poor performance was confirmed, with MEA, DUAOs, myopathies and EGUS representing the main diseases involved in fitness impairment.

A Scoping Review of Non-Structural Airway Disease as a Cause of Poor Performance in Racehorses

The association between poor performance and respiratory disease in Thoroughbred racehorses that do not have a structural abnormality of the respiratory tract, is often based on anecdotal evidence. The objective of this scoping review was to examine the scientific evidence for such associations. Publications were selected based on a search of three databases (PubMed, Scopus, and CAB Direct), in English and without date restriction, followed by a screening process to exclude non-relevant papers, duplicates, and reviews. This process identified 996 publications of which 20 were analysed using the Quality in Prognosis Studies (QUIPS) tool. The results indicated that the evidence supporting the relationship between proposed diagnostic indicators and poor performance is variable. There is a need for better quality evidence. In particular, there are conflicting reports relating to the impact of equine asthma and EIPH on athletic performance. Furthermore, a lack of standardisation in the measurement of racehorse performance makes it difficult to compare findings from different studies. The industry would benefit from high-level guidance concerning the design of controlled performance studies in Thoroughbred racehorses to collect comprehensive data and facilitate targeted interventions.

Date of birth and purchase price as foals or yearlings are associated with Thoroughbred flat race performance in the United Kingdom and Ireland

Background

Methods

Results

Conclusions

Intralesional bone marrow and superior check desmotomy is superior to conservative treatment of equine superficial digital flexor tendonitis

BACKGROUND

Superficial digital flexor tendon (SDFT) injury is common in racehorses and a significant cause of lost training days and wastage in the industry.

OBJECTIVES

To compare the post-injury performance of Thoroughbred and Standardbred racehorses diagnosed with SDFT tendonitis treated with intralesional bone marrow and superior check desmotomy or managed conservatively and further to compare this performance with that of uninjured racehorses.

STUDY DESIGN

Retrospective and case-controlled.

METHODS

Medical and race records of racehorses treated surgically or managed conservatively for SDFT tendonitis were collated. Signalment, lesion severity and treatment were identified and performance post-injury compared. Performance of the treatment groups was further assessed by comparison with uninjured racehorses matched for age, sex, number of starts pre-injury and randomly selected from the cases' last races.

RESULTS

The study population comprised 114 racehorses divided into surgical (39/114), conservative (38/114) and control groups (37/114). Horses that had surgery were more likely to return to racing than those managed conservatively (OR 4.7 95% CI [1.6-14.3], P = .006). Standardbreds were more likely to return to race compared with Thoroughbreds (OR 4.0 95% CI [1.2-13.3], P = .03). There was no statistically significant difference in the average number of placings, average number of wins and post-injury earnings between the surgically treated and conservatively managed groups (P = .9, P = .9 and P = .7, respectively). The average number of lifetime starts post-injury/post-selection between surgery, conservative and control groups were not statistically significantly different (P = .2). Surgically treated horses had a statistically significantly shorter time to start post-injury compared with the conservative group (P = .04).

MAIN LIMITATIONS

The retrospective nature of the study precludes an actual fit as a nonrandomised clinical trial and the nonrandomised nature of the allocation of the treatment groups is biased.

CONCLUSIONS

Surgical intervention of superficial digital flexor tendonitis in racehorses suffering flexor tendon injury showed a higher likelihood of return to racing than conservative treatment.

Who Is Healthy? A Review of How Equine Control Groups Are Defined in Clinical Orthopaedic Research 1999-2021

INTRODUCTION

 Proper identification of healthy subjects is essential in case-control studies. However, standardized definitions of healthy controls are lacking in equine orthopaedic research.

OBJECTIVES

 The aim of this study was to define the non-invasive methods used for selecting healthy control horses in osteoarthritis (OA), desmitis and tendinitis research.

METHODS

 Systematic review. Case-control studies with a healthy control group and longitudinal studies where horses had to be healthy at the start were included. Studies where joints were visualized by arthroscopy or post-mortem examination were excluded.

RESULTS

From 2,472 OA papers and 2,746 desmitis/tendinitis papers, 127 and 84 papers met the inclusion criteria respectively. For OA, 11 methods were identified for defining healthy subjects with a median of three methods used per paper. Dynamic examination, radiographic evaluation and clinical examination were the most frequent. Eight different methods were identified in the desmitis/tendinitis papers with a median of three methods per paper; ultrasonography, clinical- and dynamic examination were the most frequent.

CONCLUSIONS

 Overall, the OA and desmitis/tendinitis studies used similar methods for defining subjects as healthy, but the way the examinations were performed and interpreted was inconsistent. In several studies, healthy controls were not examined for lameness. The most common methods have limitations for detecting horses with early OA, which may have implications for interpretation of results. Standardized use of more sensitive and objective methods could be beneficial.

Comparative results of 3 treatments for medial femoral condyle subchondral cystic lesions in Thoroughbred racehorses

OBJECTIVES

To compare 3 different methods for treatment of medial femoral condyle (MFC) subchondral cystic lesions in Thoroughbred horses <24 months old based on the criterion of ability to race post-treatment.

STUDY DESIGN

Retrospective cohort study.

ANIMALS

Thoroughbreds (n = 107, age < 24 months) diagnosed with MFC subchondral cystic lesions.

METHODS

Medical records between January 2004 and December 2017 were reviewed. Three treatment methods were used in these horses during that time frame: arthroscopic debridement, intralesional autologous mesenchymal stem cell (MSC) injection, and intralesional corticosteroid injection. The outcome evaluated was the ability to compete in a pari-mutuel race.

RESULTS

Seventy-eight of 107 Thoroughbreds (73%) raced post-treatment; 41/57 (72%) of horses treated by arthroscopic debridement raced; 16/19 (84%) of horses treated with intralesional MSCs raced; 21/31 (68%) of horses treated with intralesional corticosteroids raced. There was no difference between groups in the ability to start a race. Sex, limb affected, and lesion size also had no effect on the ability to start a race. There was a trend for increasing lesion size reducing the probability of racing.

CONCLUSIONS

Seventy-three percent of the horses raced, but there was no difference in the ability of unraced Thoroughbreds to race after treatment of MFC subchondral cystic lesions with arthroscopic debridement, intralesional mesenchymal stem cells, or intralesional corticosteroids.

CLINICAL SIGNIFICANCE

The 3 reported treatment options may be considered for treatment of MFC subchondral cystic lesions with a good prognosis for racing post-treatment. Owners should be advised that increasing lesion size decreases the probability of racing.

Association of Thoroughbred Racehorse Workloads and Rest Practices with Trainer Success

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

Comparing racing performance following arthroscopic surgery of metacarpophalangeal/metatarsophalangeal and carpal joints in Thoroughbred racehorses rehabilitated using conventional and underwater treadmill therapies

BACKGROUND

Rehabilitation of horses using underwater treadmill therapy has been shown to improve joint range of motion, joint mobility, stride length and proprioceptive parameters with experimental studies. However, studies investigating the prognosis and return to function following rehabilitation are lacking.

METHODS

A retrospective study of Thoroughbred racehorses treated with arthroscopic surgery for osteochondral fragments of the metacarpophalangeal (MCP) or metatarsophalangeal (MTP) joints or carpal joints undergoing conventional rehabilitation or underwater treadmill assisted rehabilitation at the same facility were included. The objective of the current study was to investigate if underwater treadmill assisted rehabilitation following arthroscopy in the Thoroughbred racehorse was positively associated with returning to racing, time to return to racing and postoperative racing performance including Beyer Speed Figures.

RESULTS

Surgery was performed on 165 horses on 174 surgical occasions; 70 (40.2 per cent) underwent underwater treadmill rehabilitation, with the remainder undergoing conventional rehabilitation. The time to return to racing was a median of 227 (IQR 185-281) days and 239 (IQR 205-303) days for underwater treadmill and conventional rehabilitation, respectively (P=0.16). Of the horses that raced presurgery, 83 per cent (58/70) of underwater treadmill rehabilitated horses and 61 per cent (63/104) of horses undergoing conventional rehabilitation returned to racing following surgery (P=0.02).

CONCLUSION

Underwater treadmill rehabilitation is superior in returning a Thoroughbred racehorse to racing following arthroscopic surgery of the carpus and/or MCP/MTP joints.

Career outcome of Thoroughbred racehorses with metacarpo/metatarsophalangeal joint dorsal chip fracture managed nonsurgically and surgically: A retrospective cohort study

BACKGROUND

Arthroscopy has been advocated as the treatment of choice for dorsal osteochondral chip fracture of the metacarpo/metatarsophalangeal (MCP/MTP) joint. However, there is no published research on racing performance outcomes of horses with this pathology managed nonsurgically.

OBJECTIVES

To compare racing career outcomes of Thoroughbred racehorses with nonsurgically (non-SX) or surgically (SX) managed MCP/MTP dorsal osteochondral chip fracture alongside a cohort of horses with no dorsal osteochondral chip fracture (unexposed).

STUDY DESIGN

Retrospective cohort study conducted between 2006 and 2014.

METHODS

Radiographs of Thoroughbred racehorses were reviewed to identify MCP/MTP dorsal osteochondral chip fractures. Unexposed horses under the care of the same practice were recruited randomly from training records. Racing outcomes were analysed using survival analysis and logistic, linear and negative binomial regression techniques.

RESULTS

Dorsal osteochondral chip fractures were identified in 98 (70 non-SX, 28 SX) horses and compared with 648 unexposed horses. There was no significant difference among non-SX, SX, and unexposed horses in respect of total career starts, or likelihood of ever winning, placing, or earning money in a race (P > .05). SX horses had a significantly higher rate of wins/start than non-SX horses (rate ratio 1.6, CI 1.1-2.4, P = .02) and unexposed horses (rate ratio 1.9, CI 1.3-2.8, P = .001). Total career earnings for the SX horses were 4.1 times that of the unexposed horses (95% CI 1.2-14.5, P = .03), although total career earnings did not differ significantly between non-SX and unexposed horses (P = .8).

MAIN LIMITATIONS

Retrospective observational study where management technique was not randomised or blinded. Small number of surgically managed horses and potential selection bias for surgical management.

CONCLUSIONS

Nonsurgical management of this injury appears to be a valid management choice given that it was not associated with significant effects on racing career performance relative to a large unexposed cohort in this study population.

Racing performance after surgical repair of medial condylar fracture of the third metacarpal/metatarsal bone in thoroughbred racehorses

OBJECTIVE

To report the performance of thoroughbred racehorses after surgical repair of a medial condylar fracture of the third metacarpal/metatarsal bone.

STUDY DESIGN

Retrospective cohort study.

SAMPLE POPULATION

Forty-three horses surgically treated for medial condylar fractures, 30 with previous racing experience, 13 without previous racing experience (nonexperienced).

METHODS

Medical records (2009-2017) were reviewed for signalment, radiographic fracture characteristics, repair technique, and postoperative morbidity and mortality. Each experienced horse was matched with two horses randomly selected from its most recent race to serve as healthy controls. Racing performance parameters (race rating, competitive level, speed rating, performance index) and career racing statistics were compared with multiple regression models between injured experienced horses and controls. The career racing statistics for nonexperienced horses were evaluated. Reasons for nonreturn to racing were obtained.

RESULTS

The median duration of follow-up was 6 years (minimum 2, maximum 10). Twenty-one of 43 (49%) horses raced again as well as 18 of 30 (60%) experienced horses and three of 13 (23%) nonexperienced horses. Experienced horses were five times more likely than nonexperienced horses to return to racing (95% confidence interval = 0.07-0.58, P = .003). Higher preoperative racing performance parameters were associated with return to racing. Racing performance parameters were lower after the date of fracture in injured horses compared with controls.

CONCLUSION

Experienced horses were more likely to return to racing after medial condylar fracture repair, although their performance was generally lower than that of comparably uninjured horses.

CLINICAL SIGNIFICANCE

Owners should be aware that horses with medial condylar fractures likely will race at a lower level than their uninjured peers.

Sagittal plane slab fractures of the third carpal bone in 45 racing Thoroughbred horses

BACKGROUND

Sagittal plane slab fractures of the third carpal bone are a recognised injury in the racehorse. Currently no published data exist for the UK Thoroughbred racehorse population.

OBJECTIVES

To document return to racing following sagittal slab fracture of the third carpal bone in a UK-based racehorse population, and to compare conservative and surgical management.

STUDY DESIGN

Single centre retrospective study.

METHODS

Computerised medical and racing records were searched over a 15-year period for Thoroughbred racehorses with a simple sagittal slab fracture of the third carpal bone. Horses with comminuted fractures and short incomplete linear lucencies were excluded. Time from intervention to next race was recorded. Success rates were compared by Fisher's Exact Test and Mann-Whitney U Test.

RESULTS

Forty-seven horses, with 49 fractures met the inclusion criteria. Overall, 27 horses raced following injury (60%). Median time to first start was 251 days (115-600, IQR 109). Fifteen horses with 16 fractures were managed conservatively. Seven horses (47%) raced, 115-508 days following injury (median 240 days, IQR 306). Thirty horses underwent surgery; this involved placement of a single 3.5-mm lag screw under arthroscopic guidance. Twenty horses (67%) raced again 145-600 days following surgery (median 264 days, IQR 102). A higher proportion of horses managed surgically improved their Racing Post Rating (RPR) following injury (14/20), compared with those managed conservatively (1/7, P = .02).

MAIN LIMITATIONS

The numbers of horses are small, particularly for those managed conservatively. Treatment was not randomly allocated, and as such several horses which underwent conservative management were subsequently retired for breeding.

CONCLUSIONS

This case series indicates that both arthroscopic repair and conservative management of sagittal slab fractures of the third carpal bone allows horses to successfully return to training and racing.

Nonsurgical and surgical management of metacarpo/metatarsophalangeal joint dorsal chip fracture in the Thoroughbred racehorse

BACKGROUND

Arthroscopy is considered the treatment of choice for dorsal osteochondral chip fractures of the metacarpo/metatarsophalangeal (MCP/MTP) joints in the racehorse; however, there is no published research on non-surgical management of this injury.

OBJECTIVES

To compare clinical features, intra-articular medication use and return to racing in Thoroughbred racehorses with non-surgically (non-SX) or surgically (SX) managed MCP/MTP dorsal chip fracture.

STUDY DESIGN

Retrospective observational study conducted between 2006 and 2014.

METHODS

Radiographs of Thoroughbred racehorses were reviewed to identify MCP/MTP dorsal osteochondral chip fractures. Clinical and intra-articular medication data were obtained from veterinary records, and return to racing data from a public online resource.

RESULTS

A total of 98 MCP/MTP horses with dorsal chip fractures were identified (70 non-SX, 28 SX). Median age was 2 years (range 2-7 years). Osteochondral chip fractures predominantly involved the forelimbs (n = 92, 93.9%) and the majority were considered by the treating clinician to be clinically active (n = 85, 86.7%). Significantly more SX horses had a reported ongoing problem associated with the affected joint than non-SX horses (P = 0.002), however there was no significant difference between non-SX and SX horses in the number of intra-articular medications of affected joint per month of follow-up (P = 0.22). The proportion of horses racing post-diagnosis was not significantly different between non-SX (55/70; 78.6%, 95% CI 69.0, 88.2%) and SX horses (24/28; 85.7%, 95% CI 72.8, 98.73%) (P = 0.57). Median time to first start following diagnosis for non-SX (106 days, range 1-326) was significantly shorter than for SX horses (203 days, range 9-559) (P = 0.002).

MAIN LIMITATIONS

Management technique was not randomised or blinded, with few surgically managed horses.

CONCLUSIONS

The results contribute to the current evidence base used to guide management of osteochondral chip fractures of the MCP/MTP joints in the racehorse, and indicate that non-surgical management may be a valid treatment option for some injuries.

A 10-year study of arthroscopic surgery in racing Thoroughbreds and Quarter Horses with osteochondral fragmentation of the carpus

BACKGROUND

Osteochondral fragmentation of the carpus is a common cause of lameness in racehorses. Prognosis following arthroscopic removal of the fragments was reported in 1987, but little is known of recent success rates.

OBJECTIVE

To identify associations between the severity and location of osteochondral fragments in the carpus, and to describe the racing performance of horses pre- and post-surgery in Thoroughbreds and Quarter Horses. To identify factors associated with a horse racing post-surgery.

STUDY DESIGN

Retrospective study of clinical records (2006-2016).

METHODS

Surgical and racing records for racehorses undergoing arthroscopic surgery of the carpus were collated during the 10-year study period. Signalment, location of osteochondral fragmentation and grade of defect left after removal and debridement identified and racing performance pre- and post-surgery were described, stratified by breed. Logistic regression analysis was used to identify factors associated with unsuccessful return to racing.

RESULTS

In total, 828 horses (n = 416 Quarter Horses; n = 412 Thoroughbreds) underwent 880 carpal arthroscopies after fragments were found on radiography. Sixty-five percent (n = 289) and 27% (n = 118) of the lesions were bilateral in Quarter Horses and Thoroughbreds respectively (P<0.001). In both breeds, the most commonly affected bone was the dorsodistal radial carpal bone (n = 320/659; 48.6%). Overall, 82% (n = 686; n = 358 Quarter Horses, n = 328 Thoroughbreds) of horses raced post-surgery, with 69.5% (n = 476; n = 228 Quarter Horses, n = 248 Thoroughbreds) racing at the same or a higher level of competition. Factors associated with horses not returning to racing post-surgery were increasing horse age, female horses, and a lesion grade of 4, while racing pre-surgery was protective.

MAIN LIMITATIONS

This study does not include a control population for comparison.

CONCLUSIONS

There were significant differences between the location and severity of lesions in Quarter Horses, when compared to Thoroughbreds. The majority of horses return to racing following surgery, although performance was influenced by lesion severity. The Summary is available in Portuguese - see Supporting information.