Subchondral bone failure in overload arthrosis: a scanning electron microscopic study in horses.

The research study examines how mechanical overload can cause a common arthrosis in racehorses, leading to subchondral bone failure. The researchers investigated the progression of this bone failure by examining the bones of 25 racehorses with varying stages of the disease.

Research Methodology

• The research study focused on the metacarpal condyle of the fetlock joint of racehorses. This particular joint is commonly affected by arthrosis due to excessive mechanical load during racing. In some severe cases, the impact causes lameness in horses.
• Twenty-five fetlock condyles from different racehorses with stages of disease ranging from mild subchondral bone sclerosis to severe bone collapse were selected for this study.
• Parasagittal slices of these condyles were radiographed and examined through scanning electron microscopy to provide a detailed analysis of the bone structure.

Results and Findings

• The early signs of subchondral bone failure were fine matrix cracks in the bone layer just above the calcified cartilage. These were believed to be caused by the loss of water or other non-collagenous components in the bone structure.
• The development of microcracks was noticed in the sclerotic bone within close proximity to the calcified cartilage layer. These cracks were aligned parallel to the cartilage layer and expanded in irregular branching lines.
• As the condition worsened, larger cracks or microfractures developed gaps, resulting in fragmentation along their margins.
• There were instances of osteoclast resorption sites along the fracture lines, which indicated that activated bone remodeling may have caused a weakening in the bone structure.
• Bone collapse occurred due to the compaction of the fragmented matrix along these microfractures. If a bone collapse took place, fracture lines were noticed through the calcified cartilage. This was associated with indentation at the articular cartilage at the site of the fracture.

The study provides a deeper understanding of bone failure in racehorses and their progression. It may aid in developing effective preventative measures and treatments to mitigate the impact of this widespread issue.