Biomechanical testing of the calcified metacarpal articular surface and its association with subchondral bone microstructure in Thoroughbred racehorses.

The research explores the biomechanical properties of the hardened (calcified) joint surfaces in Thoroughbred racehorses, and its association with changes in the underlying supportive bone (subchondral bone) structure and the horses’ training history. Findings suggest that racing training influences the properties of these articular surfaces and that horses with certain types of bone fatigue injuries show reduced material properties in these surfaces.

Study Factors and Methodology

• This is a cross-sectional study conducted on the third metacarpal condyle (a part of the horse leg system) of 31 Thoroughbred horses.
• The research utilized micro-computed tomography (microCT) to examine the structure of the condyles. The hyaline cartilage, which overlies the calcified surface, was removed to facilitate testing.
• The study employed a testing technique called Reference Point Indentation (RPI) which measures the mechanical properties of the calcified surface, including its toughness.
• The Indentation Distance Increase (IDI) measured here is an inverse measure of toughness; hence a higher IDI implies reduced toughness of the surface.
• Training histories of the horses were obtained from their trainers. This data was juxtaposed against the biomechanical property measurements to find any correlation.

Key Findings

• Untrained horses had higher Indentation Distance Increase (IDI) than those who underwent training, implying that training affects the toughness of these joint surfaces.
• Horses that suffered fatal bone fatigue injuries or POD (Palmar/plantar osteochondral disease), a common ailment in racehorses were associated with higher IDI scores, pointing to decreased toughness of their calcified articular surfaces.
• The study found that connectivity density and trabecular pattern factor, aspects reflective of how the bone tissue is interconnected and structured, were associated with changes in the calcified surface’s toughness.

Conclusions

• The application of RPI to measure the mechanical properties of the calcified articular surface is unique, but the authors caution about potential variability due to surface unevenness.
• Initiation of race training was found to be associated with altered material properties of the calcified articular surfaces.
• Reduced toughness of these surfaces was also apparent in horses that had bone fatigue injuries not just in the metacarpus but other skeletal areas.
• The study suggests that the connectivity and shape of the underlying bone may be more critical in determining the articular surface’s resistance to failure rather than traditional measures like bone volume and density.