Effects of immobilization followed by remobilization on mineral density, histomorphometric features, and formation of the bones of the metacarpophalangeal joint in horses.

This research investigated the impacts of immobilization and remobilization on the long bones of the metacarpophalangeal joint in horses. The findings suggest that eight weeks of exercise after single-limb immobilization is not enough to recover the loss in bone mineral density.

Research Method and Process

• The study comprised of five healthy horses. One forelimb of each horse was immobilized with a fiberglass cast for seven weeks, followed by a remobilization period of eight weeks with increasing exercise.
• To track bone labelling and subsequent analysis, two different substances—Calcein and Oxytetracycline—were injected intravenously during both the immobilization and exercise phases.
• Upon euthanasia, the researchers examined the sagittal sections of the metacarpal bones and proximal phalanges of the horses via radiography, dual energy x-ray absorptiometry, histomorphometry, and bone label analysis.

Research Findings

• Radiography revealed a loss of bone mineral density in the subarticular regions of the immobilized metacarpal bones and phalanges, with subchondral lesions detected in metacarpal bones in two horses.
• In phalanges, there was a significant decrease in the subarticular volumetric bone mineral density.
• There were measurements of remarkably less bone volume and calcein-labeled bone surface and more vascular volume and oxytetracycline-labeled bone surface in immobilized phalanges, when compared to the contralateral (opposite side) phalanges.

Conclusions

• Based on the study results, it was concluded that eight weeks of exercise following a single-limb immobilization is inadequate for full recovery of volumetric bone mineral density.
• Additionally, findings suggest that during the periods of immobilization and remobilization, the subchondral and trabecular bone appear to be actively remodeling.

In essence, this research suggests that longer rehabilitation periods may be necessary for horses after limb immobilization to regenerate the lost bone mineral density fully. Plus, it indicates that immobilization notably affects the microstructure of the bone, leading to active remodeling during the recovery process.