Descriptive epidemiology of fractures occurring in British Thoroughbred racehorses in training

REASONS FOR PERFORMING STUDY: Musculoskeletal injury is the major cause of days lost from training and wastage in Thoroughbred racehorses. Little scientific information is available on the majority of injuries occurring in training. OBJECTIVES: To estimate the incidence of fractures in British racehorses in training and describe the occurrence of different fracture types and bones involved. METHODS: Thirteen UK racehorse trainers participated in a prospective study, providing data on horses in their care for 2 years. Details on horses, their daily exercise and fracture occurrence were recorded. RESULTS: A total of 1178 horses provided 12,893 months at risk. Nontraumatic fracture incidence was 1.15/100 horse months (95% CI = 0.98, 1.35) and 78% of fractures occurred during training. A wide variety of fracture types and bones were involved, although at least 57% were stress fractures. Pelvic and tibial stress injuries accounted for 28% of fractures diagnosed. CONCLUSIONS: It is important to study injuries in training as well as in racing. The number of stress fractures suggests that training regimes for young Thoroughbreds could often be improved to create a more robust skeleton, able to withstand injury. POTENTIAL RELEVANCE: Studying injuries in racehorses in training can provide a scientific basis for the design of safer training regimes.     

Cumulative racing-speed exercise distance cluster as a risk factor for fatal musculoskeletal injury in Thoroughbred racehorses in California

Thoroughbred racehorses which suffered a fatal musculoskeletal injury (FMI) while racing or race training at a California racetrack during 9 months of 1991 were studied to determine the importance of intensive, high-speed exercise schedules prior to injury. Seventy-seven horses which sustained an FMI while racing and 45 horses which sustained an FMI while race training were successfully matched by race or timed workout session with one control horse and included in the analyses. Race and timed workout (racing-speed exercise) histories were obtained for the case and control horses. Two-month cumulative, racing-speed cutoff distances were calculated from the control horse sample by two methods. Median racing-speed exercise frequencies and distances of the control horses were used to estimate age-specific (2, 3, 4 and ≥ 5 years), 2-month cumulative, racing-speed distances (Method 1). For the second method, the last race or timed workout for each control horse occurring just prior to, or on the date of injury for the matched case horse was identified. Cumulative racing-speed distances 2 months prior to these exercise events were determined for each control horse and used to estimate median age-specific (2, 3, 4 and ≥ 5 years), 2-month cumulative racing-speed distances (Method 2). The cumulative cutoff distances estimated from both methods were used to classify each matched pair according to the presence or absence of a 2-month cumulative, racing-speed distance which exceeded the age-appropriate cutoff distance (exercise distance cluster) within 6 months prior to injury. Manlel-Haenszel matched-pair odds ratios and 95% confidence limits were calculated separately for the racing and race-training fatal injuries. The relative risk for racing FMI was significantly greater for those horses which ran 2-month, cumulative racing and timed workout distances in excess of the cutoff values determined with Method 1 (relative risk (RR) = 3.0, 95% confidence interval (CI) = 1.2, 7.6) and Method 2 (RR = 7.2, 95% CI = 2.6, 20.6). The relative risk for race-training FMI was significantly greater for those horses which ran 2-month, cumulative racing and timed workout distances in excess of the cutoff values determined with Method 2 (RR = 3.4, 95% CI =1.0, 13.2).     

Risk factors for proximal sesamoid bone fractures associated with exercise history and horseshoe characteristics in Thoroughbred racehorses

OBJECTIVE: To assess individual and combined associations of high-speed exercise and horseshoe characteristics with risk of forelimb proximal sesamoid bone fractures and proximal sesamoid bone midbody fractures in Thoroughbred racehorses. ANIMALS: 269 deceased Thoroughbred racehorses. PROCEDURES: A case-control study design was used to compare 121 horses with a fracture of at least 1 of 4 forelimb proximal sesamoid bones (75 horses had a midbody fracture) and 148 horses without a forelimb proximal sesamoid bone fracture. Univariable and multivariable logistic regression analyses were used to evaluate potential risk factors for association with proximal sesamoid bone fracture. RESULTS: Compared with horses that died without proximal sesamoid bone fractures, horses that died with proximal sesamoid bone fractures were more likely to be sexually intact males, spend more time in active trainingand racing, complete more events, train and race longer since their last layup, have higher exercise intensities during the 12 months prior to death, and have greater cumulative distances for their career. Horses with proximal sesamoid bone midbody fractures were more likely to be sexually intact males, train and race longer since their last layup, and have higher exercise intensities during the 12 months prior to death. CONCLUSIONS AND CLINICAL RELEVANCE: Limitingexercise intensity and the continuous time spent in activity duringa horse's career may decrease the frequency of forelimb proximal sesamoid bone fractures in Thoroughbred horses.     

Quantitative analysis of scintigraphic findings in tibial stress fractures in Thoroughbred racehorses

OBJECTIVE: To develop a quantitative method of interpreting tibial scintigrams of Thoroughbred racehorses with tibial stress fractures that may facilitate diagnosis of fractures and to provide prognostic information regarding future performance of affected horses. ANIMALS: 35 Thoroughbred racehorses. PROCEDURES: Static bone-phase scintigrams of tibial stress fractures were quantitatively analyzed by use of ratios of the mean radionuclide counts per pixel in a region of interest (ROI) drawn around the area of increased uptake of radiopharmaceutical to mean counts per pixel in a second ROI drawn around an apparently normal area of the tibial diaphysis. In horses with unilateral fractures, ratios for the contralateral tibia were determined by use of 2 ROIs drawn at the same positions as the ROIs in the fractured tibia. Ratios were compared between fractured versus apparently normal tibias, between horses that returned to racing versus those that did not, and among horses with various grades of lameness. The association between ratios for fractured tibias and intervals between diagnosis and return to racing was also assessed. RESULTS: Mean ratio of ROIs in apparently normal tibias was 1.35 (95% confidence interval [CI], 1.21 to 1.50); that in tibias with stress fractures was 3.55 (95% CI, 2.50 to 4.60). These ratios were significantly different. None of the associations between ratios for fractured tibias and grades of lameness or performance outcomes were significant. CONCLUSIONS AND CLINICAL RELEVANCE: Tibial stress fracture scintigrams can be quantitatively analyzed. A prospective study with a controlled rehabilitation period is necessary to evaluate the possible applications of this method.     

Descriptive epidemiology of fracture,tendon and suspensory ligament injuries in National Hunt racehorses in training

Reasons for performing study: While fractures and tendon injuries are known to be important diseases in National Hunt (NH) racehorses during racing, there are no accurate estimates of their incidence in NH training yards. Objectives: To estimate the incidence of fractures and tendon and suspensory ligament injuries (TLIs) in NH racehorses in training; to describe the injuries incurred and to compare injury incidence rates by horse age, trainer, gender and background (ex‐flat vs. ex‐store horses). Methods: Cohort data were collected from 14 UK NH training yards for 2 racing seasons. Daily exercise regimens and details of fractures and TLIs occurring in study horses were recorded. Results: Data were gathered from 1223 horses that spent 9466 months at risk of injury. The fracture incidence rate was 1.1/100 horse months and varied significantly by trainer (P<0.001) but not by gender, age or background. The pelvis and third metacarpal bone (MCIII) were the most common fracture sites, although this varied between racing and training. The TLI incidence rate was 1.9/100 horse months and varied significantly by trainer (P = 0.05) and age (P<0.001) but not by gender or background. However, exstore horses were significantly more likely to have a TLI on the racecourse than ex‐flat horses (P = 0.01). Superficial digital flexor injuries accounted for 89% of all TLIs, the remainder being suspensory ligament injuries. Conclusions and potential relevance: Fractures and TLIs are important causes of morbidity and mortality in NH racehorses in training in England. This study provides accurate estimates of their incidence in this population and provides a baseline against which to monitor the effect of future interventions.     

Evaluation of detailed training data to identify risk factors for retirement because of tendon injuries in Thoroughbred racehorses

OBJECTIVE: To identify the risk factors for premature retirement because of tendon injury in a Thoroughbred racehorse population. ANIMALS: 175 Thoroughbred racehorses (cases) at the Hong Kong Jockey Club that were retired from racing because of tendon injury between 1997 and 2004 and for which the last preretirement exercise was at a fast pace were each matched with 3 control horses that were randomly selected from all uninjured horses that had galloped on the same date as that last exercise episode. PROCEDURES: Training data for all horses were examined. Conditional logistic regression analyses were performed to identify risk factors for retirement from racing attributable to tendon injury. Two multivariable conditional logistic regression models were created; each contained 8 explanatory variables. RESULTS: Compared with control horses, case horses were older at the time of import, accumulated more race distance soon after import, were more likely to have had previous official veterinary or ultrasonographic examinations, raced fewer times during their career, and were in training for a longer period and had exercised at a reduced intensity during the 180-day period preceding the last fast-paced work date. CONCLUSIONS AND CLINICAL RELEVANCE: In addition to identification of risk factors for tendon injury among racing Thoroughbreds, results have suggested that resources focused on obtaining accurate training data may be misdirected in the absence of internationally agreed criteria for incident tendon injury among racehorses. Nevertheless, changes in training intensity and findings of previous clinical examinations could be used to identify horses at risk of tendon injury-associated retirement.     

Stress fractures of the tibia and humerus in Thoroughbred racehorses: 99 cases (1992-2000)

OBJECTIVE: To determine clinical characteristics of and outcome in Thoroughbred racehorses with tibial or humeral stress fractures. DESIGN: Retrospective study. ANIMALS: 99 Thoroughbreds with tibial or humeral stress fractures. PROCEDURE: Information obtained from the medical records included history, signalment, and clinical, radiographic, and scintigraphic findings. Outcome was determined by interviewing trainers, performing follow-up examinations, and analyzing race records. RESULTS: Seventy-four tibial stress fractures were identified in 61 Thoroughbreds, and 48 humeral stress fractures were identified in 39 Thoroughbreds (1 horse was included in both groups). Tibial stress fractures occurred most commonly in 2-year-old or unraced horses. Fractures were located in 1 of 3 sites in the tibia (most commonly, the caudolateral cortex of the mid-diaphysis) and 1 of 4 sites in the humerus (most commonly, the caudodistal cortex). Forty-four of 58 (76%) tibial stress fractures and 18 of 32 (56%) humeral stress fractures were identified radiographically. Humeral stress fractures involving the caudodistal cortex were not detected radiographically. Treatment consisted of rest and exercise restriction, and 49 of 61 (80%) horses with tibial stress fractures and 30 of 39 (77%) horses with humeral stress fractures returned to racing. Humeral stress fractures recurred in 6 horses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that in Thoroughbred racehorses, tibial stress fractures occurred most commonly in unraced 2 year olds, whereas humeral fractures occurred most commonly in older horses that had raced previously. The prognosis for racing following treatment was good.     

Arthroscopic removal of fracture fragments involving a portion of the base of the proximal sesamoid bone in horses: 26 cases (1984-1997)

OBJECTIVE: To determine the outcome of horses with basal fractures of the proximal sesamoid bone from which a fracture fragment involving a portion of the base of the bone was removed arthroscopically and to determine whether fragment size was associated with outcome. DESIGN: Retrospective study. ANIMALS: 26 horses. PROCEDURE: Dorsopalmar and axial-abaxial lengths of the fracture fragment were measured on the dorsopalmar and mediolateral radiographic views, respectively, and percentage of the base of the sesamoid bone involved was estimated. Fractures were classified as grade 1 (< or = 25% of the base involved) or grade 2 (> 25% but < 100% of the base involved). Outcome was classified as successful if the horse started at least 2 races or unsuccessful if the horse started only 1 race or failed to return to racing. RESULTS: There were 24 racehorses and 2 nonracehorses. Twelve (50%) of the racehorses returned to racing and started at least 2 races. Eight of 14 horses with grade-1 fractures and 4 of 10 horses with grade-2 fractures had a successful outcome. Ten of 16 horses without associated articular disease had successful outcomes, compared with 2 of 8 horses with associated articular disease. However, fragment size and presence of associated articular disease were not significantly associated with outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with basal fractures of the proximal sesamoid bone from which a fracture fragment involving a portion of the base of the bone is removed arthroscopically have a fair prognosis for return to racing.     

A case-crossover study of intensive racing and training schedules and risk of catastrophic musculoskeletal injury and lay-up in California Thoroughbred racehorses

The objective of this study was to investigate the relationship between intensive racing and training schedules and risk of either catastrophic musculoskeletal injury (CMI) or lay-up from racing in California Thoroughbreds. Thoroughbred racehorses that sustained a CMI during racing or training and either were subsequently euthanized or died on a California racetrack during 1991 and 1992 were studied using a case-crossover study design. Each study subject (case) provided its own self-matched control information in the form of ‘typical’ exposure frequency, determined or estimated from historic information. Periods of rapid average daily accumulation of high-speed exercise distance were identified for each horse from official race and training histories with a sliding 60-day window. Those window frames containing an average daily rate of distance accumulation exceeding 75th percentile cutoff values were classified as exposed frames followed by 30 days of increased risk, or hazard periods. All remaining days (excluding periods of layoff from racing) were considered non-hazard time at risk. The relative risk (RR) of CMI within 30 days following a period of rapid accumulation of high-speed exercise distance (during a hazard period) was 4.2 (95% confidence interval [CI]= 3.0, 5.8). Of these 214 cases, 84 (39%) were injured during a hazard period whereas on average only 22% of total career time at risk was hazard time for these horses. A second analysis was performed for horses with at least 1 lay-up period from racing of ≥ 60 days. RR for a lay-up beginning during a hazard period was estimated for the last lay-up experienced by each horse. The RR for lay-up beginning during a hazard period was 4.8 (95% CI = 2.9, 8.1). Of these 98 cases, 32 (33%) of the lay-ups began during a hazard period whereas on average, only 22% of at-risk time up to last lay-up was hazard time for these horses.     

Scapula stress fractures in Thoroughbred racehorses: Eight cases (1997–2006)

No case series exists in the literature describing scapula stress fractures. The purpose of this study was to review the clinical findings, diagnostic images and outcome of 8 horses diagnosed with scapula stress fractures. Scapula stress fractures were seen in Thoroughbred racehorses displaying acute moderate forelimb lameness. Nuclear scintigraphy identified the mid‐distal scapula spine and/or scapula supraspinous fossa as predilection sites. Conservative management resulted in a good prognosis for return to racing, but stress fracture recurrence may be seen.     

Characteristics of Thoroughbred and Quarter Horse racehorses that sustained a complete scapular fracture

Reasons for performing study: To determine if scapular fractures occur in racehorses with distinctive characteristics. Objectives: To test the hypothesis that Thoroughbred (TB) and Quarter Horse (QH) racehorses with a scapular fracture have similar characteristics that are different from those of their respective racetrack populations. Methods: Necropsy findings, case details, last race information and career earnings for TB and QH racehorses that had a scapular fracture in California between 1990 and 2008 were retrospectively compared between breeds. Horse signalment, career earnings, career starts and race characteristics were obtained for all California racehorses. Comparisons were made between affected horses, other racehorses that died, and all horses that raced, in California during the 19 year period. Results: Seventy‐three TB and 28 QH racehorses had a similar, complete comminuted scapular fracture with an articular component, and right forelimb predilection. The QHs had a higher incidence of scapular fracture incurred during racing than TBs (0.98 vs. 0.39/1000 starters). The TB and QH incident rates for musculoskeletal deaths incurred racing were 20.5 and 17.5/1000 starters, respectively; however, a greater proportion of TB musculoskeletal deaths occurred training (40% vs. 8%). Horses with a scapular fracture were more likely to be male and aged 2 or ≥5 years than the racetrack population. Most affected QHs (64%) were 2‐year‐olds; most TBs (74%) were aged ≥3 years. Scapular fractures occurred more commonly during racing in QHs (70%) than TBs (44%). Race‐related scapular fracture was more likely to occur in a Maiden race than in a non‐Maiden race. Horses with a scapular fracture had fewer career starts than the racetrack population. Conclusions and potential relevance: Despite breed differences for signalment and exercise distances, both breeds incur a complete scapular fracture that is more likely to occur in the right scapula of young and older, male racehorses, early in their race career or after few races. Quarter Horses sustain a catastrophic scapular fracture more frequently than TBs.     

Training-related factors associated with dorsometacarpal disease in young Thoroughbred racehorses in the UK

REASONS FOR PERFORMING STUDY: Dorsometacarpal disease (DMD) is common in young Thoroughbred (TB) racehorses, often interfering with their training programme. No reports exist on incidence rate or associated risk factors in the UK. OBJECTIVES: To estimate the incidence rate of DMD in TB horses in training for flat racing in the UK and identify associated risk factors, particularly in relation to training regimens. METHODS: Data were drawn from a large prospective study in which TB horses in 13 training yards were monitored for a period of up to 2 years, recording daily training information and details of musculoskeletal injury, including DMD. The incidence of DMD was calculated and survival analysis performed to determine features of the training regimen related to the risk of disease. RESULTS: A total of 335 horses provided 4235 months at risk of DMD. Seventy-nine first episodes were recorded, resulting in an incidence rate of 1.87/100 horse months (95% confidence interval 1.50-2.33). Increasing exercise distances at canter and high speed in short periods (up to 1 month) were associated with an increasing risk of DMD. However, increasing cumulative exercise distances since entering training were associated with a decreasing risk of the disease. CONCLUSIONS: The risk of DMD in young TBs decreases with accumulation of distances exercised at canter and high speed; this reflects the adaptive response of the third metacarpal bone to the loads placed upon it. However, increasing exercise distances in short periods (up to 1 month) increases the risk of DMD, probably as a consequence of microdamage and its associated remodelling response, and should therefore be avoided. POTENTIAL RELEVANCE: Training regimens for young TBs can be adjusted to prevent the occurrence of DMD. Early but gradual introduction of small amounts of high-speed exercise may be beneficial. Canter exercise should be kept minimal on high-speed work days and large amounts of both cantering and high-speed work per week, 2 weeks or per month should be avoided, particularly during the early stages of training, in order to minimise the risk of DMD.     

Risk factors for musculoskeletal injuries of the lower limbs in Thoroughbred racehorses in New Zealand

AIM: To investigate risk factors for injury to musculoskeletal structures of the lower fore- and hind-limbs of Thoroughbred horses training and racing in New Zealand. METHODS: A case-control study analysed by logistic regression was used to compare explanatory variables for musculoskeletal injuries (MSI) in racehorses. The first dataset, termed the Training dataset, involved 459 first-occurrence cases of lower-limb MSI in horses in training, and the second, the Starting dataset, comprised a subset of those horses that had started in at least one trial or race in the training preparation that ended with MSI (n=294). All training preparations for horses that did not suffer from MSI for which complete data were available were used in the analyses as controls, and provided 2,181 and 1,639 preparations for the Training and Starting datasets, respectively. Multivariate logistic regression was used to evaluate risk factors, and results were reported as odds ratios (OR) and 95% confidence intervals (CI). RESULTS: Horses aged > or =5 years were at higher risk of injury than 2-year-olds. Elevated odds of MSI occurred in horses in the Starting dataset that were training in the 1997-1998 year compared with the 1999-2000 year, and in those horses where trials comprised >20% of all starts in a preparation. Training preparations that ended in winter, and horses in their third or later training preparation, had lower odds of MSI compared with those ending in other seasons or the first preparation, respectively. Reduced odds of MSI were observed in preparations in which starts occurred compared with those that had no starts, and in the Starting dataset, preparations that included more than one start had a reduced likelihood of MSI compared with preparations that had only one start. In the Training dataset, preparations longer than 20 weeks were associated with reduced odds of MSI compared with those shorter than 20 weeks. Cumulative racing distance in the last 30 days of a training preparation was best modelled with linear and quadratic terms. Results indicated that increasing cumulative racing distances were associated with an initial reduction in the odds of MSI that then levelled out and finally appeared to increase again as the explanatory variable continued to increase. The risk of MSI varied significantly between trainers. CONCLUSION: This study identified intrinsic (age) and extrinsic risk factors for MSI in training and racing Thoroughbreds in New Zealand. The risk of MSI initially decreased, then increased, as cumulative racing distance increased. Significant variation between trainers indicated management and training methods influence the risk of MSI.     

Associations between physiotherapy findings and subsequent diagnosis of pelvic or hindlimb fracture in racing Thoroughbreds

Reasons for performing study: Physiotherapists who work in racehorse training yards routinely treat horses' backs and hindquarters and may be able to recognise signs that indicate the presence of (impending) pelvic or hindlimb fracture before it becomes catastrophic. Objective: To establish whether physiotherapy assessment findings in Thoroughbred racehorses referred for routine physiotherapy could be predictive of subsequent (within 30 days) pelvic or hindlimb fracture diagnosis. Methods: Retrospective veterinary and physiotherapy data from a cohort of Newmarket (UK) Thoroughbred racehorses, were used. A case‐control study compared physiotherapy assessment findings of racehorses with and without a subsequently diagnosed pelvic or hindlimb fracture. Uni‐ and multivariable logistic regression was used to investigate and quantify the strength of association between physiotherapy findings and subsequent fracture diagnosis. Statistical significance was set at P<0.05. Results: A total of 513 horses provided 14 fracture cases for analysis. Presence of pelvic bony asymmetry, muscle atrophy of the quarters, reduced reflex movements of dorsi‐ and/or ventroflexion and spasm or tenderness on palpation of the gluteal muscles were significantly associated with subsequent fracture diagnosis in univariable analysis. Multivariable analysis indicated that horses subsequently diagnosed with pelvic or hindlimb fracture were 11.1 times more likely to show pelvic bony asymmetry, 4.7 times more likely to display muscle atrophy of the quarters and 6.6 times more likely to have spasm or tenderness on palpation of the gluteal muscles than those that were not. Conclusions: Racehorses presented for physiotherapy that show pelvic bony asymmetry, muscle atrophy of the quarters and/or spasm or tenderness on palpation of the gluteal muscles should alert the physiotherapist to the potential presence of (impending) pelvic or hindlimb fracture. Potential relevance: Earlier detection of (impending) pelvic or hindlimb fracture in racing Thoroughbreds could reduce the incidence of catastrophic fractures.     

STRESS REMODELING AND STRESS FRACTURE OF THE HUMERUS IN FOUR STANDARDBRED RACEHORSES

Two 2-year-old pacers, a 3-year-old pacer and a 2-year-old-trotter with acute forelimb lameness were admitted for nuclear scintigraphic examination. Horses were grade 3-4/5 lame. There was increased radiopharmaceutical uptake (IRU) in the distal cranial medial aspect of the humerus in one horse and along the caudal humeral cortex in the other three horses. Two of the four horses were affected bilaterally. Radiographic abnormalities consisted of thickening of the caudal cortex of the mid-diaphysis of the humerus but radiographic changes were not present in all horses. All horses were managed with stall rest initially then stall rest with hand-walking followed by limited turn out for a total of four months. None of the horses had raced before injury. One horse has returned to race training and the other three horses have returned to racing. Average time to return to racing was 329 days. Humeral stress fractures in Standardbred horses are rare. Diffuse patterns of IRU have not been reported in the humerus and are likely indicative of severe stress remodeling. Standardbred racehorses with stress fractures or stress remodeling of the humerus appear to have a good prognosis for return to racing.     

Macroscopic changes in the distal ends of the third metacarpal and metatarsal bones of Thoroughbred racehorses with condylar fractures

OBJECTIVE: To determine changes in the distal ends of the third metacarpal and metatarsal bones (MCIII and MTIII) of Thoroughbred racehorses that had sustained a catastrophic condylar fracture during high-speed exercise. SAMPLE POPULATION: Fractured and contralateral MCIIIs and MTIIIs from 11 Thoroughbred racehorses that sustained a displaced condylar fracture during racing, both MCIIIs from 5 Thoroughbred racehorses euthanatized because of a catastrophic injury other than a condylar fracture, and both MCIIIs from 5 horses of other breeds that had not been professionally trained or raced. PROCEDURE: Macroscopic observations were made of the distal ends of the bones before and after digestion of the articular cartilage with NaOH. RESULTS: In all 11 racehorses with a displaced condylar fracture, the fracture was associated with a branching array of cracks in the condylar groove. In this region, fracture margins were smooth, and there was loss of subchondral bone. Comminution of the dorsal cortex was also seen. Parasagittal linear wear lines in the articular cartilage, erosions in the articular cartilage of the condyles, loss of the underlying subchondral bone, and cracking of condylar grooves were all more severe in the Thoroughbred racehorses than in the horses that had not been professionally trained or raced. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that condylar fractures in horses are pathologic fatigue or stress fractures that arise from a preexisting, branching array of cracks in the condylar groove of the distal end of MCIII or MTIII.     

Risk factors for and outcomes of noncatastrophic suspensory apparatus injury in Thoroughbred racehorses

OBJECTIVE: To evaluate effects of toe grabs, exercise intensity, and distance traveled as risk factors for subclinical to mild suspensory apparatus injury (SMSAI) in Thoroughbred racehorses and to compare incidence of severe musculoskeletal injury (MSI) in horses with and without SMSAI. DESIGN: Nested case-control study. ANIMALS: 219 Thoroughbred racehorses racing or in race training. PROCEDURE: Racehorses were examined weekly for 90 days to determine incidence of suspensory ligament injury and monitor horseshoe characteristics. Every horse's exercise speeds and distances were recorded daily. Conditional logistic regression was used to compare exposure variables between incident case (n = 25) and selected control (125) horses. Survival analysis was used to compare time to MSI for horses with (n = 41) and without (76) SMSAI. RESULTS: The best-fitting logistic model for the data included age (< 5 vs > or = 5 years old), toe grab height the week of injury (none vs very low, low, regular, or Quarter Horse height), and weekly distance the week preceding injury (miles). Although the 95% confidence intervals for all odds ratios included 1, the odds for SMSAI appeared to increase with the presence of a toe grab, higher weekly distance, and age > or = 5 years. Horses that had SMSAI were significantly more likely to have a severe MSI or severe suspensory apparatus injury than were horses that did not. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that pre-existing SMSAI is associated with development of severe MSI and severe suspensory apparatus injury. Modifying training intensity and toe grab height for horses with SMSAI may decrease the incidence of severe MSI.     

Intralesional injection of platelet-rich plasma followed by controlled exercise for treatment of midbody suspensory ligament desmitis in Standardbred racehorses

OBJECTIVE: To determine outcome of Standardbred racehorses with moderate to severe midbody suspensory ligament desmitis (MSD) treated by means of ultrasound-guided intralesional injection of a single dose of platelet-rich plasma (PRP) followed by a program of gradually increased exercise. DESIGN: Nonrandomized clinical trial. ANIMALS: 9 Standardbred racehorses. PROCEDURES: Following injection of PRP, horses were allowed a controlled, gradual return to exercise. Race records for the year prior to injury and for 3 consecutive years after horses returned to racing were reviewed. For comparison purposes, race records of 9 Standardbred racehorses with no history of MSD racing at the same time were also reviewed. RESULTS: All 9 horses with MSD returned to racing after treatment; median time to return to racing was 32 weeks. All 9 horses raced at least once during the first and second years after returning to racing, but only 5 raced during the third year. When number of starts, total earnings, and earnings per start were compared between case and comparison horses, the only significant differences were number of starts during the third year after case horses returned to racing and earnings per start during the first year after case horses returned to racing, with values being significantly lower for case horses than for comparison horses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that horses with moderate to severe MSD treated by means of intralesional injection of a single dose of PRP followed by a program of gradually increased exercise had an excellent prognosis for returning to racing.     

Evaluation of horseshoe characteristics and high-speed exercise history as possible risk factors for catastrophic musculoskeletal injury in thoroughbred racehorses

OBJECTIVE: To evaluate horseshoe characteristics and high-speed exercise history as risk factors for catastrophic musculoskeletal injury in Thoroughbred racehorses. ANIMALS: 377 horses (37,529 race starts). PROCEDURES: Shoe characteristics included material, toe grab height, heel traction device, pads, and rim shoes. Racing variables were obtained from a computerized database. Forty-three horses that had a musculoskeletal injury and then failed to race or train for 6 months (cases) and 334 noninjured horses from the same race in which a horse was injured (controls) were compared regarding risk factors. RESULTS: Overall, 98% of race starts were associated with aluminum shoes, 85% with toe grabs, 32% with pads, and 12% with rims on forelimb horseshoes. Among 43 horses with musculoskeletal injury, sex (geldings), an extended interval since last race, and reduced exercise during the 30 or 60 days preceding injury were risk factors for catastrophic injury. Odds of injury in racehorses with toe grabs on front shoes were 1.5 times the odds of injury in horses without toe grabs, but this association was not significant (95% confidence interval, 0.5 to 4.1). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that horses that return to racing after an extended period of reduced exercise are at high risk of catastrophic musculoskeletal injury. Results regarding the use of toe grabs as a possible risk factor for catastrophic injury were inconclusive because the probability of declaring (in error) that use of toe grabs was associated with an increased risk of musculoskeletal injury (eg, odds ratio > 1.0) was 38%.     

Horse-level risk factors for fatal distal limb fracture in racing Thoroughbreds in the UK

REASONS FOR PERFORMING STUDY: Fractures below the level of the radius or tibia (distal limb fractures) are the most common cause of equine fatality on UK racecourses; however, little is known about their epidemiology or aetiology. Identification of risk factors could enable intervention strategies to be designed to reduce the number of fatalities. OBJECTIVES: To identify horse-level risk factors for fatal distal limb fracture in Thoroughbreds on UK racecourses. METHODS: A case-control study design was used. Fractures in case horses were confirmed by post mortem examination and 3 matched uninjured controls were selected from the race in which the case horse was running. One hundred and nine cases were included and information was collected about previous racing history, horse characteristics and training schedules. Conditional logistic regression was used to identify the relationship between a number of independent variables and the likelihood of fracture. RESULTS: Horses doing no gallop work during training and those in their first year of racing were at significantly increased risk of fracture on the racecourse. Case horses were also more likely to have trained on a sand gallop, i.e. a gallop described by trainers as being primarily composed of sand. CONCLUSIONS: Modifications to training schedules, specifically within the first year of racing, may have a large impact on the risk of fatal distal limb fracture on the racecourse. Horses should do some gallop work in training and our results suggest that the minimum distance galloped should be between 805-2012 m (4-10 furlongs)/week. POTENTIAL RELEVANCE: The information from this study can be used to alter training schedules in an attempt to reduce the incidence of fatal distal limb fracture in Thoroughbred racehorses. Training should include some gallop work, and further studies, recording the exact level of work, will help to identify an optimum range of training speeds and distances which will reduce the liklihood of catastrophic fracture on the racecourse.