How do metacarpophalangeal joint extension, collateromotion and axial rotation influence dorsal surface strains of the equine proximal phalanx at different loads in vitro?

This research investigated how different load conditions, joint movements, and rotations affect the strains on a specific bone in a horse’s leg, with a view to better understand common fractures in this area. The study found that strain increases with movement and rotation, and made promising insights into the causes of sagittal fractures in horses.

Study Purpose and Objectives

• The study aimed to gain a better understanding of the biomechanics of the equine metacarpophalangeal joint (MCPJ) and potential reasons for sagittal fractures in the proximal phalanx (P1) bone, part of a horse’s leg.
• The study’s objectives were to measure changes in P1 bone strains, collateromotion (side-to-side movement), and axial rotation (turning) during MCPJ extension, which is the process of straightening the joint, in a controlled environment.

Methods

• The study used limbs of six horse cadavers and placed markers on the bones to track their movements relative to each other when loaded with different forces, up to 10,500 Newtons.
• The movements were recorded and analyzed during the extension of the MCPJ.
• At the same time, the strains (deformation resulting from stress) on the dorsoproximal P1 bone surface were measured with strain gauges.

Results

• The research found that axial rotation and collateromotion increased with MCPJ extension. The greatest principal strain increased linearly as the load varied from 2000 to 10,500 Newtons.
• Minimum principal and maximum shear strains were found to have curvilinear relationships with limb loading, showing negligible strain until approximately 6000N, after which strain rapidly increased.
• The direction of the minimum principal strain on the P1 bone shifted by about 30-40 degrees as the load increased, moving from a proximolateral-distomedial (from the upper side to the lower middle) to a nearly proximodistal direction (from top to bottom).

Conclusion

• Findings suggest that near maximum MCPJ extension, combined with axial rotation and collateromotion, leads to a rapid increase in strain on the P1 bone, along with a change in the direction of the principal strain.
• The changes observed in strain magnitude and direction could help explain the occurrence of sagittal P1 fractures in horses and contribute to a more comprehensive understanding of equine leg biomechanics.