Overload arthrosis: strain patterns in the equine metacarpal condyle.

The research explores patterns of strain in the equine metacarpal condyle, a joint in a horse’s leg, during overload arthrosis, a degenerative condition in joints caused by excessive strain. The study examines how differing degrees of bone sclerosis, a thickening and hardening of bone, distributed force through the joint under different conditions.

Methodology

• The study took samples of joints in varying states of sclerosis, ranging from mild to severe. It also examined joints where collapse, a serious potential consequence of sclerosis, was imminent.
• These bone slices were then subjected to forces simulating the pressure exerted by the sesamoid bone, a bone embedded within a tendon aiding joint movement, during different stages of a horse’s gait cycle.
• The research employed contact radiography to examine changes in the bone under these forces. By tracking changes in the pattern of the bone’s structures, the study was able to establish the strains created by these forces.

Results

• The study found that strain levels were proportional to the forces applied and were greatest during the midstance phase of gait, when the joint is supporting most of the horse’s weight.
• Strain patterns were different across samples and different loading positions, suggesting variability in how stresses are distributed through joints.
• As sclerosis of the underlying subchondral bone, or the layer of bone beneath the joint’s cartilage, increased, the study found increased shear strain in the overlaying structures called trabeculae, the spongy part of bone that supports and reduces weight in the joint.
• However, no consistent strain pattern was identified where devitalization, the process of bone cells dying, or mechanical failure occurs. This suggests the strain distribution varies, potentially based on factors not examined in this study.
• Higher strains sometimes occurred at the joint surface in relation to the edge of the platen, a model sesamoid bone, suggesting that the sesamoid bone’s position and forces may contribute to the onset of arthrosis.

Conclusion

• In summary, the study found that the process of sclerosis in subchondral bones redistributes stress throughout the joint, particularly to the trabeculae, which can lead to increased strain in those areas. However, no consistent pattern of strain indicating areas of potential mechanical failure or devitalization was found. The sesamoid bone’s interaction with the joint was identified as potentially having an effect on strain pattern, indicating future avenues for research.