A retrospective study of catastrophic pelvic fractures in California Thoroughbred racehorses.

Overview

• This study investigates catastrophic pelvic fractures in Thoroughbred racehorses in California by analyzing autopsy reports from 1992 to 2018.
• The research compares affected horses’ exercise histories with matched control horses to identify characteristics and potential risk factors linked to pelvic fractures.

Study Design and Data Collection

• Retrospective review of autopsy reports from California racehorses that died naturally or were euthanized due to complete pelvic fractures.
• Study period spanned 26 years, from 1992 to 2018.
• Exercise history data of affected horses were compared against matched control horses to understand differences in training and racing patterns.

Key Findings on Pelvic Fractures

• Total of 133 horses sustained catastrophic pelvic fractures during the study period.
• Pelvic fractures accounted for 2.7% of all musculoskeletal fatalities in racehorses.
• Timing of fractures:
  • 48.0% occurred during training sessions.
  • 35.0% occurred during actual races.
  • 17.0% occurred during non-exercise periods.
• Age distribution:
  • 73.5% of pelvic fractures occurred in horses aged 4 years or younger.
  • 26.5% occurred in horses aged 5 years or older.
• Sex distribution:
  • Females had a higher incidence of fractures (68.1%) compared to geldings (23.1%) and intact males (8.8%).
• Bilateral fractures (fractures on both pelvic sides) were seen in 46.9% of cases.
• The ilium (a major pelvic bone) was fractured in 90.3% of horses, either alone or with other pelvic bones.
• Bilateral iliac wing fractures (fractures on both sides of the ilium) occurred in 28.4% of cases.

Preexisting Conditions and Fracture Characteristics

• Preexisting periosteal calluses (new bone growth indicative of prior bone injury) were present in 31.9% of horses with pelvic fractures.
• 88.9% of these calluses were associated specifically with ilial fractures, indicating prior injury at the same site.

Outcomes and Mortality

• 25.7% of horses with complete pelvic fractures died spontaneously (without euthanasia).
• Among spontaneous deaths, 89.6% were due to massive internal bleeding caused by lacerated blood vessels associated with the fracture.

Exercise and Racing History Comparison

• Horses with pelvic fractures:
  • Participated in fewer races spread further apart in time.
  • Exercised less intensely throughout their careers.
  • Experienced more frequent lay-ups (periods of rest or non-racing activity).
  • Had 31% less overall exercise time and 40% fewer competitive events since their last lay-up compared to control horses.

Implications and Recommendations

• The study suggests that preexisting injuries, such as those indicated by periosteal calluses, may contribute to the risk of catastrophic pelvic fractures.
• Identifying these factors early could help in diagnosis, treatment, and prevention strategies for racehorses.
• Recommendations include monitoring horses for signs of preexisting pelvic injuries and considering modifications in training regimens to reduce fracture risk.