Cartilage damage involving extrusion of mineralisable matrix from the articular calcified cartilage and subchondral bone.

The study is about a unique pathology that affects articular calcified cartilage and subchondral bone in Thoroughbred racehorses, likely due to repetitive overload arthrosis. The pathology is associated with hyaline articular cartilage degeneration and has no significant association with other variables like the number of racing seasons, age, earnings, or training duration.

Introduction

• The research explores a peculiar pathology observed in the joints of Thoroughbred racehorses. Specifically, the scientists investigate afflictions of the articular calcified cartilage (ACC) and subchondral bone (SCB), the parts most implicated in overload arthrosis – damage resulting from repetitive strain on the joints.
• The condition has been associated with degeneration of the hyaline articular cartilage (HAC), a tissue that enables smooth movement of the joints.

Methodology

• The researchers examined portions from the left third metacarpal/metatarsal bones from 39 trained Thoroughbred racehorses that were euthanized due to welfare reasons.
• Several imaging techniques, including point projection microradiography, backscattered electron scanning electron microscopy (BSE SEM), light microscopy, and confocal scanning light microscopy, were used to study the tissue samples.
• They also used nanoindentation, a method to measure mechanical properties of tissues at the nanometer scale, to analyse the stiffness of the extruded matrix.
• Data related to the horses’ training and racing career were collected to understand if any aspect of their experience had influenced the onset or severity of the condition.

Findings

• The researchers found highly mineralized projections originating from cracks in the ACC mineralizing front, extending up to two-thirds of the thickness of the HAC, and corresponding with surface fibrillation directly over their location.
• Through nanoindentation, they determined that this extruded matrix was notably stiffer than any other mineralized phase in the sample by a magnitude of two.
• There was a significant association between the presence of these projections and a high cartilage Mankin histology score (a grading system for evaluating severity of damaged cartilage) and instances of cartilage loss on the condyle, implying a pathological condition.
• The presence of projections showed no significant correlation with variables such as total number of racing seasons, horse age, earnings, total distance galloped in a career, training duration, or presence of wear lines.

Conclusion

• The study identifies a unique pathology associated with repetitive overload arthrosis, fundamentally impacting the ACC and SCB in Thoroughbred racehorses.
• This research could potentially provide critical insights for addressing similar joint issues in humans, where the phenomenon of cartilage degeneration plays a similar role in conditions such as osteoarthritis.