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

Area of Science:

• Equine orthopedics
• Veterinary pathology
• Biomechanical analysis

Background:

• Mechanical overload frequently causes arthrosis in the metacarpal condyle of the fetlock joint in racehorses.
• Severe forms of this condition can lead to lameness, often associated with subchondral bone failure.

Purpose of the Study:

• To investigate the progression of subchondral bone failure in racehorse fetlocks, from microcracks to bone collapse.
• To analyze the relationship between microstructural changes in subchondral bone and articular cartilage damage.

Main Methods:

• Examination of 25 racehorse fetlock condyles at various stages of disease using radiography and scanning electron microscopy.
• Analysis of parasagittal slices to identify microcracks, fragmentation, and bone collapse in the subchondral bone layer.

Main Results:

• Earliest microcracks were observed in sclerotic bone, 1-3 mm from the calcified cartilage layer, extending parallel to it.
• Fragmentation and gaps formed along crack margins, with evidence of osteoclastic resorption indicating remodeling-induced weakening.
• Bone collapse resulted from matrix compaction along microfractures, correlating with calcified cartilage fractures and articular cartilage indentation.

Conclusions:

• Subchondral bone failure in racehorse fetlocks progresses through microcrack formation, fragmentation, and eventual collapse.
• These microstructural changes are directly linked to traumatic osteochondrosis and articular cartilage damage.
• Understanding this progression is crucial for managing and preventing fetlock joint pathology in equine athletes.