Histological Features of the Distal Third Metacarpal Bone in Thoroughbred Racehorses, With and Without Lateral Condylar Fractures.

This research examined the distal third metacarpal bone of thoroughbred racehorses, studying histopathological markings present on magnetic resonance imaging (MRI) to understand the clinical implications of such abnormalities. Significantly, the study found correlations between the severity of changes in superficial and deeper osteochondral tissues, the number of race starts, and scores of articular cartilage damage.

Methodology

• The horses’ metacarpal bones were observed and categorized based on features noticed through MRI.
• Sections of these bones were taken and treated for histopathological examination, looking specifically at the articular cartilage (the smooth, white tissue covering the ends of bones where they come together to form joints) and the subchondral bone (the layer of bone just below the cartilage).

Scoring System

• The detected lesions in the bones were scored using a system partly based on the grading system from the Osteoarthritis Research Society International.
• The system involved ranking the severity of a lesion.

Data Analysis

• The researchers used descriptive statistics and linear mixed effects models to analyze the collected data.

Results

• A positive correlation was found between the severity of alterations in superficial and deeper osteochondral tissues, and between the number of race starts and the articular cartilage score.
• No correlation was found between age and either the articular cartilage or subchondral bone scores.
• There was moderate variation seen in articular cartilage and subchondral bone scores, but individual bones showed differences as well.

Specific Findings

• Bones that showed focal palmar necrosis (cellular death in a specific area on the palm side of the hand) had significant differences in the histological scoring of the articular cartilage in comparison to bones that didn’t show this phenomena.
• Bones displaying incomplete fractures or large areas of bone remodelling showed notable differences in subchondral bone pathology when compared with bones with focal palmar necrosis.
• Haematoidin, a blue-colored by-product of hemoglobin breakdown, often associated with local hemorrhage, was found in areas with excessive subchondral bone and both hardened and/or irregular bone density, indicating poor blood circulation in these areas.