Training practices, speed and distances undertaken by Thoroughbred racehorses in Victoria, Australia.

BACKGROUND: Musculoskeletal injuries (MSI) in racehorses are commonly due to bone fatigue, a function of the number of cycles (strides) and the magnitude of load applied to the limb. These parameters can be estimated using speed and distance, with greater than 6000 m/month at a gallop (>14 m/s), in combination with canter distances greater than 44,000 m/month, reported to increase fracture risk. Despite their importance, there are limited data on the distances and speeds horses are exposed to during training. OBJECTIVES: Estimate training volume at different speeds undertaken by Australian Thoroughbred racehorses. STUDY DESIGN: Cross-sectional study. METHODS: Registered trainers (n = 66) in Victoria, Australia were surveyed. Questions were designed to assess the full training workload from initial pre-training to training performed to achieve and maintain race fitness, as well as information on rest periods. Descriptive analyses were stratified by trainer- and horse-level factors, with assessment of variance within and between groups. Cluster analyses were used to identify similar workload intensity groups. RESULTS: Horse-level factors (age, targeted race distance) were associated with workload (younger

Associations between pre-injury racing history and tibial and humeral fractures in Australian Thoroughbred racehorses.

Long bone fractures in racehorses may present as stress fractures which have a good prognosis, or complete fractures, which often result in a fatal outcome. In order to identify differences in modifiable management practices that may contribute to these outcomes, racing histories of horses with humeral or tibial fractures and of matched controls were examined. A retrospective case-control study of Australian Thoroughbred racehorses diagnosed with a fracture of the humerus or tibia by scintigraphy or at post-mortem between 2002 and 2016 was undertaken. Control horses were matched from the same race or trial on age and sex. Statistical analysis was performed using conditional logistic regression, χ2 and Mann-Whitney U tests. More humeral fractures than tibial fractures were fatal (12/47, 26% vs. 3/35, 8.6%, P = 0.049). No differences in pre-injury racing histories were observed between cases and controls for humeral and tibial fractures. Both humeral and tibial fracture case horses were younger than the registered Thoroughbred racing population (P < 0.001), but horses sustaining humeral fractures were older than those with tibial fractures (3.3 ± 0.9 vs. 2.8 ± 0.8 years, P = 0.005) yet raced fewer times prior to the injury (0.5 ± 1.1 vs. 1.3 ± 1.7 races, P = 0.009). Horses with fatal humeral fractures were less likely to have raced than those with non-fatal humeral fractures (16.7% vs. 55.6%, P = 0.02). In conclusion, tibial and humeral fractures occur in young racehorses, and humeral fractures are more likely to be fatal in those with the least exposure to trialling and racing.

Solar angle of the distal phalanx is associated with scintigraphic evidence of subchondral bone injury in the palmar/plantar aspect of the third metacarpal/tarsal condyles in Thoroughbred racehorses.

BACKGROUND: Subchondral bone injury at the palmar/plantar aspect of the condyles of the third metacarpal/metatarsal bone (MC/MT3) commonly causes lameness and poor performance in racehorses. Injury occurs due to repetitive loading, the magnitude of which may be influenced by the position of the distal phalanx relative to the ground surface, i.e. the solar angle. The association of solar angle and injury at the palmar/plantar condyles of distal MC/MT3 therefore warrants investigation. OBJECTIVES: Investigate the relationship between solar angle and radiopharmaceutical uptake at the palmar/plantar aspect of distal MC/MT3 on scintigraphic images of racehorses. STUDY DESIGN: Retrospective case-controlled study. METHODS: Scintigraphic images of Thoroughbred racehorses presented for poor performance or lameness were graded for intensity of radiopharmaceutical uptake in the palmar/plantar aspect of distal MC/MT3. Solar angle was graded (positive, neutral or negative), referring to the angle of the solar plane of the distal phalanx relative to the ground surface. Repeatability of solar angle (n = 1226 limbs) and agreement with objective radiographic evaluation (n = 52 limbs) were evaluated. Prescintigraphy performance data were collected from race records. Associations between solar angle, performance and radiopharmaceutical uptake were investigated using multivariable logistic regression. RESULTS: Repeatability of scintigraphic solar angle grading (κ = 0.89, 95% CI 0.87-0.91) and agreement of scintigraphic and radiographic solar angle (κ = 0.88, 95% CI 0.75-0.97) were excellent. Horses that performed best prior to presentation were more likely to have both greater radiopharmaceutical uptake and a neutral/negative solar angle. When controlling for prior performance, horses with neutral/negative forelimb solar angle were twice as likely to have moderate/marked radiopharmaceutical uptake than horses with positive solar angle (P<0.02). Horses with negative hindlimb solar angle were six times more likely to have moderate/marked radiopharmaceutical uptake than horses with positive/neutral solar angle (P<0.001). MAIN LIMITATIONS: Population bias due to preselected hospital population. CONCLUSIONS: Both solar angle and race performance are independently associated with increased bone activity in the palmar/plantar aspect of the third metacarpal/tarsal condyles. The Summary is available in Portuguese - see Supporting Information.

Osteopetrosis in a neonatal donkey.

Osteopetrosis is a rare disorder characterised by a defect in osteoclastic bone resorption. This report describes osteopetrosis in a neonatal donkey that suffered a displaced tibial fracture. Radiographic examination identified generalised reduction in medullary cavity size, thickened mid-diaphyseal cortices and conical metaphyseal bone extending toward the mid-diaphysis of long bones. Postmortem examination identified additional fractures and brittle bones. Histologically, osteoclasts were absent in multiple bone sections. Diaphyseal cortices consisted of concentric bone lamellae with marrow tissue infiltration. Large wedges of secondary spongiosa extended from the metaphyseal growth plate. Clinical and histopathological features were similar to an osteoclast-deficient, autosomal recessive form of osteopetrosis in humans.

Retrospective study of outcome following desmotomy of the accessory ligament of the deep digital flexor tendon for type 1 flexural deformity in Thoroughbreds.

OBJECTIVE: Determine the long-term outcome for Thoroughbreds undergoing desmotomy of the accessory ligament of the deep digital flexor tendon (DAL-DDFT) for type 1 flexural deformity of the distal interphalangeal joint (DIPJ). DESIGN: Retrospective matched cohort study PROCEDURE: Medical records were retrieved over a 17-year period for Thoroughbreds that underwent DAL-DDFT for type 1 flexural deformity. Long-term outcome was determined by analysis of race records and comparison with maternal siblings. Comparisons between cases and controls included 2-year-old, 3-year-old and total career performance data. RESULTS: There were 46 cases of DAL-DDFT. The mean age at surgery was 151 days (median 118, range 2-562); 48% of case horses and 77% of 90 controls started in a race. For case horses that did race, the time to first race, total number of starts and prize money per race were not significantly different to maternal siblings. Age at the time of surgery did not alter the likelihood of starting a race. CONCLUSION: Thoroughbreds undergoing DAL-DDFT for type 1 flexural deformity of the DIPJ are less likely to race when compared with their maternal siblings. For those that do race, the time to first race, total races and earnings per race are not different from controls. There is no evidence to suggest that age at the time of surgery influences the likelihood of racing.

Retrospective investigation of prognostic indicators for adult horses with infection of a synovial structure.

OBJECTIVE: To investigate predictors of survival and athletic function in adult horses with infection of a synovial structure. HYPOTHESES: Increasing duration from contamination to referral, bone or tendon involvement and positive microbial culture decreases short-term survival. Synovitis and/or sepsis at 5 days post-admission and involvement of Staphylococcus spp. decreases long-term athletic function. DESIGN: Retrospective study. METHODS: Records over 4 years of adult horses with synovial sepsis were reviewed. A two-tailed Fisher's exact test, Mann-Whitney U test or t-test was used to examine whether variables were predictive of short-term survival and long-term athletic function. RESULTS: During the study period 75 horses underwent treatment for infection of 93 synovial structures. Short-term survival was 84% (63/75) and 54% (30/56) of horses returned to athletic function. Of the variables measured at admission, duration from contamination to referral did not affect survival, whereas evidence of bone or tendon involvement decreased survival and athletic function. Of the variables available during treatment, abnormal synovial fluid at 4-6 days post-admission and positive microbial culture reduced athletic function. Staphylococcal infection was associated with persistent sepsis. CONCLUSIONS: Of the variables available at presentation, only evidence of bone or tendon involvement negatively affected survival and athletic function. During treatment of synovial sepsis, analysis of synovial fluid at 4-6 days and bacterial culture results have prognostic value.

Muscle strain injuries of the hindlimb in eight horses: diagnostic imaging, management and outcomes.

OBJECTIVE: To describe the clinical presentation, ultrasound findings, management and outcome in horses with muscle tear injuries of the hindlimbs. DESIGN: Retrospective case series Procedure Medical records of eight horses were reviewed and information on signalment, history, presenting complaint, physical examination findings and further diagnostic tests were recorded. Diagnosis of muscle injury was determined by the presence of abnormal ultrasound findings, compared with the contralateral limb, and, when required, nuclear scintigraphy. Follow-up information was obtained via telephone interviews with owners, trainers and referring veterinarians. RESULTS: Muscle tears causing lameness were identified in the middle gluteal (3), semitendinosus (1), semimembranosus (2) and gracilis (2) muscles. Tears were classified by ultrasound imaging as partial (6) or complete (2). The degree of lameness did not appear to be indicative of the extent of injury or of completion of healing. Long-term follow-up was available for seven horses and the outcome was favourable in six cases. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonography is useful in the diagnosis and assessment of moderate to severe muscle strain injuries. The prognosis appears to be favourable in most cases, although recurrence of injury and lameness can delay the return to athletic activity and an inferior outcome with persistent gait abnormality may occur.