An investigation of the relationship between race performance and superficial digital flexor tendonitis in the Thoroughbred racehorse

Reasons for performing study: There is limited information regarding the number of races and the period for evaluation of outcome which is critical for assessment of SDF tendonitis treatments. Objective: To evaluate the re‐injury rate and racing performance of Thoroughbred racehorses that sustain SDF tendonitis in relation to matched controls in terms of number of races post treatment and maximum racing performance ratings before and after injury. Study design: Clinical records and racing histories of 401 racehorses with a first occurrence of SDF tendonitis diagnosed by ultrasonography. Controls were of the same age, sex and were horses training in the same establishment at the time of injury as the case horses and where the trainer reported that the horse had not had a previous SDF tendon injury or treatment. Results: Eighty percent of both case and control horses returned to racing after the date of injury, and the re‐injury proportion within 3 years of treatment was 53%. The difference in Racing Post Rating_(max) (RPR_(max)) and the Racing Post Rating in the race immediately before the treatment date was significantly smaller in case horses (mean = 9.6 lbs; range = 0–75) compared to control horses (mean = 17.0 lbs; range = 0–79). No significant decrease in RPR_(max) was noted post injury. No difference between case and control horses was found for return to racing and racing 3 times, but control horses were significantly more likely to compete 5 races post treatment date than case horses. Conclusion and clinical relevance: Injury was associated with an individual's pre‐injury maximum performance level and return to racing and completion of 3 races are not useful indicator of the outcome of horses with SDF tendonitis. The assessment of the outcome of horses with an SDF injury in a population of racehorses using the number of races post injury requires a minimum of 5 races post injury to be a useful indicator. Further, a re‐injury proportion in a population of horses in training for 3 years post treatment.     

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.     

The association of 2‐year‐old training milestones with career length and racing success in a sample of Thoroughbred horses in New Zealand

Reasons for performing study: There is increasing evidence that exercise early in life has a positive effect on musculoskeletal health. At present, there is little whole population research investigating the effect of racing as 2‐year‐olds on future racing career. Objectives: To investigate the association between attaining training milestones as 2‐year‐olds with length of career and racing success in Thoroughbred horses in New Zealand. Methods: Retrospective data were obtained of the 2001/02‐born Thoroughbred foal crop. The 3 training milestones were: registered with a trainer, trialled and raced. The association of the training milestones with career length was measured using the outcomes: number of race starts and number of years raced, in a Cox regression model. Logistic regression models analysed the association of the training milestones with the outcomes: won or placed in a race. Linear regression was performed to assess the association of training milestones with total career earnings. Results: Of 4683 horses in the population; 3152 horses were registered with a trainer, 2661 horses trialled and 2109 horses raced. Horses that raced as 2‐year‐olds had significantly (P<0.001) more race starts than those first raced as 3‐year‐olds or older, this was also true when the 2‐year‐old year data were omitted. Horses that raced as 2‐year‐olds had significantly (P<0.001) more years racing. Horses registered with a trainer, trialled or raced as 2‐year‐olds were more likely to have won or been placed in a race than those that achieved the milestones as 3‐year‐olds or older. Horses that first trialled and raced as 2‐year‐olds had greater total earnings than those that first trialled or raced at a later age. Conclusions and potential relevance: Two‐year‐old training milestones had a strong association with positive racing career outcomes. Horses in training or racing as 2‐year‐olds may have better musculoskeletal health throughout life than horses that are first in training or racing at a later age.     

Experimental infection of caprine arthritis-encephalitis virus in sheep

AIM: To describe outcomes for horses diagnosed with incomplete, non-displaced fractures of the frontal plane of the radial facet (INFR) of the third carpal bone (C3) treated by placement of a lag screw across the fracture under arthroscopic guidance.

METHODS: Horses (n=13) diagnosed with INFR and treated between December 1999 and January 2005 using a lag screw placed over the fracture were studied. For each case, five horses matched for sire, age and sex which were not known to have INFR were sought for comparison. Racing performance data were collected from a commercial online database. The racing performance of cases pre- and post-operatively, and of cases and matched horses in the post-operative period was compared.

RESULTS: Sixteen INFR were found in the 13 horses. Radiographic evidence of healed fracture lines 2–4 months after surgery was seen in 11/16 (69%) fractures; 11/13 (85%) cases raced again after a median recovery period of 292 (range 149–681) days. Treatment was considered successful in 9/13 (69%) cases, which were still in training or had been retired for reasons other than lameness localised to the middle carpal joint at the end of the study period. Just 6/13 (46%) cases had raced prior to injury. The racing ability pre- and post-operatively of five cases was compared, three (60%) of which performed better post-operatively than they had before. There was no significant difference in racing longevity or ability post-operatively between patients and matched (control) horses.

CONCLUSIONS: Post-operatively, there was little difference in the racing performance between horses diagnosed with INFR which had a lag screw placed across the fracture line and horses matched for sire, age and sex which were not known to have INFR.

CLINICAL RELEVANCE: Horses which were diagnosed with INFR of C3 and had a lag screw placed across the fracture had a good prognosis for future racing performance.     

Nonsurgical management of type II fractures of the distal phalanx in 48 Standardbred horses

OBJECTIVE: To evaluate nonsurgical management of type II fractures of the distal phalanx in Standardbred horses. DESIGN: Retrospective study of 48 affected horses. RESULTS: Most fractures occurred on the lateral palmar process of the left forelimb or the medial palmar process of the right forelimb; 81% of horses were considered sound enough to return to training and 63% raced. Of those returning to racing, 41% competed in > 10 races, 37% in 2 to 10 races and 22% in only 1 race. There was no difference in performance before and after fracture. Twenty-four of 25 horses had a bar shoe fitted for > 50% of the treatment phase. Of those horses returning to training without a bar shoe, 89% refractured at the same site. Sixty percent of horses returning to training with a bar shoe raced successfully. The total convalescent time, the time rested in a box and the time spelled in a paddock were similar for horses returning to racing and those that did not. The age of the horse had no effect on the ability to return to racing. CONCLUSION: The prognosis for type II fractures of the distal phalanx is guarded. It is advisable to fit a bar shoe on the horse during convalescence. Horses returning to training and racing with a bar shoe appear less likely to refracture the distal phalanx. Those horses that return to racing can perform at a level similar to that prior to fracture.     

Outcome of lag-screw treatment of incomplete fractures of the frontal plane of the radial facet of the third carpal bone in horses

AIM: To describe outcomes for horses diagnosed with incomplete, non-displaced fractures of the frontal plane of the radial facet (INFR) of the third carpal bone (C3) treated by placement of a lag screw across the fracture under arthroscopic guidance. METHODS: Horses (n=13) diagnosed with INFR and treated between December 1999 and January 2005 using a lag screw placed over the fracture were studied. For each case, five horses matched for sire, age and sex which were not known to have INFR were sought for comparison. Racing performance data were collected from a commercial online database. The racing performance of cases pre- and post-operatively, and of cases and matched horses in the post-operative period was compared. RESULTS: Sixteen INFR were found in the 13 horses. Radiographic evidence of healed fracture lines 2-4 months after surgery was seen in 11/16 (69%) fractures; 11/13 (85%) cases raced again after a median recovery period of 292 (range 149-681) days. Treatment was considered successful in 9/13 (69%) cases, which were still in training or had been retired for reasons other than lameness localised to the middle carpal joint at the end of the study period. Just 6/13 (46%) cases had raced prior to injury. The racing ability pre- and post-operatively of five cases was compared, three (60%) of which performed better post-operatively than they had before. There was no significant difference in racing longevity or ability post-operatively between patients and matched (control) horses. CONCLUSIONS: Post-operatively, there was little difference in the racing performance between horses diagnosed with INFR which had a lag screw placed across the fracture line and horses matched for sire, age and sex which were not known to have INFR. CLINICAL RELEVANCE: Horses which were diagnosed with INFR of C3 and had a lag screw placed across the fracture had a good prognosis for future racing performance.     

Conservative treatment of intra-articular distal phalanx fractures in horses not used for racing

OBJECTIVE: To determine the success rate and whether specific patient and treatment factors influenced the outcome after conservative treatment with a bar shoe with quarter clips of intra-articular fractures of the distal phalanx in horses not used for racing. DESIGN: Retrospective study. SAMPLE POPULATION: Thirty-two client-owned horses. PROCEDURE: Hospital records of horses that had been treated conservatively for intra-articular fractures of the distal phalanx at Skara Equine Hospital or Halland Animal Hospital in Sweden between 1995 and 2001 were reviewed. Racehorses in active training and horses affected with other musculoskeletal diseases were excluded from the study. Follow-up was performed by questionnaire and telephone inquires to the owners 1 to 7 years after injury. RESULTS: Twenty-two horses (69%) returned to their previous or expected level of use and did not wear their bar shoe when they were put back into training. There was no statistically significant correlation between outcome and patient or treatment variables, or bony union of the fracture. CONCLUSIONS AND CLINICAL RELEVANCE: Conservative treatment of intra-articular fractures of the distal phalanx carries a fair prognosis for return to previous or expected level of use in horses not used for racing. Radiographic evidence of fracture healing and age of the patient do not seem to influence the prognosis. Horses not used for racing do not need to be shod with a bar shoe with quarter clips for the rest of their athletic career.     

Compression bone plating of a medial condylar fracture of the third metatarsal bone in a Thoroughbred filly

A medial condylar fracture of the third metatarsal bone in a 2-year-old Thoroughbred filly was repaired successfully by use of compression bone plating. At discharge from the hospital, thickening of the metatarsus was evident, and proliferative changes were associated with the site of bone plate application. It was expected that these changes would limit the filly's use as a racehorse, and a return to training was not recommended. Especially in horses that may return to racing, use of compression bone plating initially should not replace stall rest or lag screw fixation treatment of this type of injury. However, the use of a similar approach in selected cases of medial condylar fracture of the third metatarsal bone is encouraged, especially when additional fissure lines are evident on radiographs.     

Results of treatment of 145 fractures of the third metacarpal/metatarsal condyles in 135 horses (1986-1994).

The objectives of this study were to correlate condylar fracture characteristics and type of treatment with subsequent capacity for athletic ability, and to determine the characteristics of healing that affect prognosis after fracture fixation. Medical records, post operative radiographic studies and race records were examined for 135 horses sustaining 145 fractures. Sixty-five percent of horses overall started in a race post injury (SPI) in a mean time of 9.7 months with a mean of 13.7 races post injury. Having raced pre-injury did not confer an advantage to starting post injury, though nonstarters pre-injury tended to take longer to return. For horses starting pre- and post injury, 66% improved or maintained their race class level after injury, whereas 64.2% decreased their race earnings post injury. Eighty-five percent of the fractures received internal fixation, of which 70% were complete fractures. Eighty-seven percent of horses with incomplete-nondisplaced fractures treated conservatively raced post injury. The percent SPI for incomplete-nondisplaced, complete-nondisplaced and complete-displaced fractures treated with internal fixation were 74%, 58%, and 60%, respectively. Males (72%) raced post injury more frequently than fillies (53%), and may represent a truer probability of SPI. Spiral fractures tended to take longer until their first start (mean 13.3 months). Fifty-two percent of horses with articular fragments were able to race post injury. Horses were more likely to start if 2-4 month radiographic healing revealed no evidence of the fracture except the presence of lag screws. Based on this series of cases, the majority of horses, with proper treatment, were able to return to racing regardless of fracture characteristic. Prognosis appeared to be affected by the severity of the injury to the joint, the presence of articular comminution and the quality of surgical repair.     

Apical fracture of the proximal sesamoid bone in standardbred horses: 43 cases (1990-1996).

OBJECTIVE: To determine whether fracture fragment dimensions, suspensory ligament damage, and racing status at the time of injury were associated with outcome in Standardbred horses with apical fracture of the proximal sesamoid bone. DESIGN: Retrospective study. ANIMALS: 43 Standardbred racehorses. PROCEDURE: Medical records, racing records, and radiographs were reviewed, and ultrasonographic findings were scored. Measurements of the fractured portion of the proximal sesamoid bone were made. RESULTS: Seventy-four percent (32/43) of horses were pacers, and 26% (11/43) were trotters. Statistical differences between trotters and pacers regarding ability to start, number of starts, or amount of money earned after injury were not detected. Females earned significantly more money per start after injury than males. Eighty-six percent (37/43) of fractures involved hind limbs and 14% (6/43) involved forelimbs. Horses with forelimb injuries earned less money per start. Severity of suspensory ligament damage did not affect postinjury racing performance. A higher proportion of horses that had raced before injury returned to racing after surgery than horses that had not raced before injury, although a significant difference between these groups was not detected. Eighty-eight percent of horses that raced before injury raced after injury. Fifty-six percent of horses that did not race before injury raced after injury. Fracture fragment dimensions did not affect outcome. CLINICAL IMPLICATIONS: Dimensions of the apical fracture fragment of the proximal sesamoid bone in Standardbred horses and degree of suspensory ligament damage did not affect outcome. Prognosis for return to racing soundness is good in horses that had raced before injury and fair in horses that had not raced before injury.     

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.     

Bacterial culture of septic synovial structures of horses: Does a positive bacterial culture influence prognosis?

Reasons for performing study: The influence of synovial fluid culture on short‐ and long‐term prognosis of cases with septic synovitis requires study. Hypotheses: Horses with a positive bacterial culture from septic synovial fluid are less likely to survive or return to successful athletic function than those with a negative bacterial culture from septic synovial fluid. Methods: Records of mature horses presented to 2 equine referral hospitals for investigation of suspected septic synovitis were examined. Horses (n = 206) were included in the study if synovial fluid was submitted for full laboratory examination, including bacterial culture. A diagnosis of septic synovitis was based on a nucleated cell count >30 × 10⁹ cells/l or >90% neutrophils and other clinical, cytological and bacteriological parameters. Long‐term follow‐up was obtained by telephone questionnaire. Univariate analysis, using the Fisher's exact test, was used for all outcomes. Results: Fourteen (20.9%) of 67 horses with a positive bacterial culture from synovial fluid were subjected to euthanasia because of persistent synovial sepsis compared to 2 (1.44%) of 139 with negative bacterial cultures (P<0.001). Overall survival and successful long‐term return to function in horses with a positive bacterial culture was 50% (24/48 horses) compared to 70.5% (74/105) in culture negative horses (P = 0.01). In horses that survived to be discharged, successful long‐term return to function was not significantly different between culture positive and culture negative groups. Growth of Staphylococcus aureus from synovial fluid did not affect short‐term survival to discharge from the hospital compared to other positive bacterial culture; however, successful long‐term return to function was only 30.4% (4/13) in horses from which S. aureus was cultured compared to 73.9% (17/23) of horses in which other bacteria were cultured (P = 0.015). Conclusions and potential clinical relevance: Horses with a positive bacterial culture from a septic synovitis have a poorer prognosis for survival to discharge from hospital and overall long‐term return to function than horses that yielded no bacterial growth. When S. aureus was cultured, the long‐term prognosis was poorer.     

Diagnosis and management of proximal sesamoid bone fractures in the horse

Fractures of the proximal sesamoid bones (PSBs) range in severity from simple to complex and comminuted and can be articular or nonarticular. The majority of PSB fractures are diagnosed in racehorses, but PSB fractures, especially simple ones, do occur in sport horses undertaking various disciplines. For simple apical, basilar and abaxial articular PSB fractures, surgical removal via arthroscopy carries the best prognosis for return to athletic performance. Removal of apical and abaxial PSB fractures generally result in a favourable prognosis for return to racing but are dependent on the amount of suspensory ligament injury. Removal of basilar PSB fracture fragments results in a less favourable or fair prognosis for return to racing. Mid‐body PSB fractures typically require (lag screw) surgical fixation preferably with arthroscopic guidance and carry a fair to guarded prognosis for return to racing.     

Surgical and nonsurgical management of sagittal slab fractures of the third carpal bone in racehorses: 32 cases (1991-2001)

OBJECTIVE: To compare results (ie, return to racing and earnings per race start) of surgical versus nonsurgical management of sagittal slab fractures of the third carpal bone in racehorses. DESIGN: Retrospective study. ANIMALS: 32 racehorses (19 Thoroughbreds, 11 Standardbreds, and 2 Arabians). PROCEDURE: Medical records and radiographs were reviewed to obtain information regarding signalment and treatment. Follow-up information was obtained from race records. Robust regression analysis was performed to evaluate earnings per start in horses that raced at least once before and after injury. RESULTS: 22 (69%) horses raced at least once after treatment of the fracture. All 7 horses treated by means of interfragmentary compression raced after treatment, and horses that underwent interfragmentary compression had significantly higher earnings per start after the injury than did horses treated without surgery. Eight of 9 horses treated by means of arthroscopic debridement of the damaged cartilage and bone raced after treatment, but only 7 of 16 horses treated without surgery (ie, stall rest) were able to return to racing after treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that racehorses with sagittal slab fractures of the third carpal bone have a favorable prognosis for return to racing after treatment. Horses treated surgically were more likely to race after treatment than were horses treated without surgery.     

Arthroscopic removal of fractures of the lateral malleolus of the tibia in the tarsocrural joint: A retrospective study of 13 cases

There is limited information on the treatment of lateral malleolus (LM) fractures in the horse, with no previously published case series for the outcome following arthroscopic removal of such fractures. This report reviews and evaluates findings of a retrospective study of 13 horses admitted to a private equine referral hospital over a 10 year period (1999–2009) that underwent arthroscopic removal of fractures of the LM. Hospital records were reviewed and details including patient history, aetiology of the fracture and limb affected, results of all diagnostic tests and surgical reports were documented. Performance information concerning Thoroughbred horses that went onto race post operatively was collected using an online database. Owners and trainers were contacted regarding the return to performance for non‐Thoroughbred cases or those that did not go onto race post operatively. Of the 13 horses presented, 12 were Thoroughbreds, 9 of which were National Hunt racehorses and 3 were Flat racehorses. The other horse in the study was used for general purpose riding. All cases presented with an acute unilateral fracture. Eleven of the 13 had >6 months post operative follow‐up and all were nonlame. Of the 12 Thoroughbreds, 10 have raced again, a total of 104 times (median 5 times). The median time from surgery to return to racing was 241 days (180–366 days). It is concluded that horses with fractures of the LM have an excellent prognosis for return to full athletic performance following arthroscopic debridement; and that arthroscopic fragment removal is an appropriate treatment method for fractures of the LM.     

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.     

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.     

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).     

The prevalence of temporal bone fractures is high in horses with severe temporohyoid osteoarthropathy

Temporohyoid osteoarthropathy is a well‐recognized cause of equine neurologic disease. Temporal bone fractures associated with temporohyoid osteoarthropathy have been recognized with CT, however, little information is available regarding these fractures. The aims of this retrospective analytical study were to assess the prevalence of these fractures and to describe the specific configurations and associated imaging and clinical features. Fracture of the temporal bone was identified with CT in 16 of 39 included horses. All fractures were unilateral, minimally displaced and extended through the temporal bone in a rostrodorsal to caudoventral orientation. Two fracture configurations were identified: in nine cases, the fracture extended the full width of the petrous pyramid into the cranial vault and in seven cases, the fracture only extended through the lateral part of the petrous temporal bone, not involving the cranial vault. Fusion of the temporohyoid joint was present in 13 of the 16 fracture cases. Quarter Horses were over‐represented in the fractured population (14/16). All horses with fractures had ipsilateral neurologic deficits. Patient outcomes were not significantly different between temporohyoid osteoarthropathy horses with and without temporal bone fractures (P = 0.68). However, six of the nine patients with cranial vault involvement did not return to their previous use. Findings support previous studies indicating that temporal bones should be carefully assessed for concurrent fractures when temporohyoid osteoarthropathy is identified in CT images, especially when there is fusion of the temporohyoid joint. An improved awareness of specific fracture configurations will help with detection of these fractures.