A postmortem grading system for articular cartilage loss of the dorsoproximal aspect of the proximal phalanx of Thoroughbred racehorses.

Overview

• This research developed a grading system to assess cartilage damage on a specific bone (proximal phalanx, P1) of Thoroughbred racehorses.
• The study compared horses that suffered catastrophic fractures to those euthanized for other reasons to understand cartilage damage related to injury and racing demands.

Background

• The metacarpophalangeal (front limb) and metatarsophalangeal (hind limb) joints undergo high motion and compression during galloping, making them injury-prone in racehorses.
• In New Zealand, the proximal phalanx (P1) is a common site of race-day fractures, but details about cartilage lesions in this bone were lacking prior to this study.
• Understanding cartilage damage on P1 helps clarify joint health and injury mechanisms in racing horses.

Study Design and Methods

• The researchers collected 102 proximal phalanges (P1 bones) from Thoroughbred racehorses that underwent postmortem exams.
• Horses were divided into two groups:
  • Fracture cohort: 18 horses euthanized due to catastrophic fractures.
  • Control cohort: 16 horses euthanized for non-musculoskeletal reasons.
• They developed a modified 3-point scoring system to grade cartilage damage on the dorsoproximal surface of P1:
  • Score 0 = No cartilage damage
  • Score 1 to 3 = Increasing severity of cartilage damage

Key Findings

• There was no significant difference in cartilage scores between fracture and control groups, suggesting cartilage loss in this region may not directly predict fracture risk.
• Cartilage damage was higher on the medial aspect (inner side) of the left forelimb and right hindlimb.
  • This aligns with biomechanical stress since New Zealand horses race counterclockwise, putting more strain on these limbs.
• Cartilage damage scores increased with horse age and number of career starts.
  • Suggests that wear and tear accumulate over time and repeated racing.
  • Indicates reduced ability of cartilage to repair as horses grow older.

Interpretation and Implications

• The grading system developed provides a standardized way to describe cartilage condition on the dorsoproximal P1 surface in racehorses.
• The lack of difference between fracture and control groups suggests other factors besides cartilage loss may contribute to catastrophic fractures of P1.
• Medial limb cartilage damage patterns support the idea that repetitive strain from racing direction influences joint wear.
• Age-related increase in cartilage damage underscores the importance of considering cumulative effects of racing over a horse’s career.
• These insights could help trainers, veterinarians, and researchers monitor joint health and potentially inform preventative strategies for joint injuries.