Evaluation of increased subchondral bone density in areas of contact in the metacarpophalangeal joint during joint loading in horses.

This study examined how horse’s bones react under different stress loads, particularly with increased density in subchondral bone (underlying layer of bone in joints) in the metacarpophalangeal joints (knuckle-like joints in the forelimbs). Evidence suggested that as load increased, contact area as well as bone density increased.

Methods

• Forelimbs were obtained from six horses without any musculoskeletal disease. The choice of horses free from musculoskeletal disease was to ensure the reliability of the results.
• Computed tomographic scans of the intact metacarpophalangeal joints were taken for the measurement of subchondral bone density.
• Each limb was placed on a materials testing system and extended to 150 degrees and 120 degrees in the metacarpophalangeal joint.
• The joint was then stained with either safranin-O or toluidine blue injection. These stains highlight changes in bone and joint tissue, making it easier to observe and measure.
• The joint was disarticulated (separated), and the surface area was digitized. This provided a high-resolution, quantitative measurement of the surface area for analysis.
• Calculations were made for total articular surface area, contact area, and percentage contact area at each angle. This was done for the distal third metacarpal condyles, the proximal phalanx, and the proximal sesamoid bones. These measures helped determine how different parts of the joint are impacted by load.

Results

• With increased load, there was a significant growth in the contact area on the third metacarpal condyles, proximal sesamoid bones, and the proximal phalanx, supporting the hypothesis that increased load results in increased contact area.
• Computed tomographic scans seemed to reveal a higher density in areas of contact. However, these high density areas appear to be subjective and vary in their visual interpretation.

Conclusions

• Areas which remained consistently in contact under a higher load were correlated with increased subchondral bone density. This lends credence to the theory that the subchondral bone adapts to the load it is subjected to.
• As the load increased, the contact area also expanded, suggesting that those areas not normally subjected to load may experience high stress during high impact loading situations.
• The quantification of how contact in the joint varies under different loading conditions, and the bone’s adaptation to this change can provide insight into both normal and abnormal joints.
• These observations and quantitative data may also provide valuable insights into the development of osteochondral diseases and their pathogenesis.