Multidirectional in vivo strain analysis of the equine radius and tibia during dynamic loading with and without a cast.

This research studied how casts impact strain distribution in horse limb bones (radius and tibia) during movement. It found that while casts change the direction of the most significant tension, they may not actually help stabilize fractures and could add stress to the fracture site.

Methods and experiments

• The research utilized rosette strain gauges, which are devices used to measure strain, or deformation, on a material’s surface. The gauges were applied to the equine radius and tibia, two long bones found in a horse’s forelimb and hindlimb respectively.
• The researchers focused their tests on three different sites of each bone – the proximal metaphysis, mid-diaphysis, and distal metaphysis.
• At each site, four gauges were used, placed at different directions around the bone – cranial (toward the head), caudal (toward the tail), medial (toward the middle), and lateral (toward the side).
• Strain data were recorded while the horse was walking, under two scenarios: with a full-limb plaster cast, and without.

Findings on strain direction and impact of casts

• The major axis of tensile strain, or the direction in which the most significant tension was observed, was found on the craniolateral aspect of the radius, meaning it was facing both the head and side of the horse.
• However, the largest observed strains at the distal end of the radius were torsional, indicating a twisting deformation.
• The application of a cast changed the primary tension direction on the radius from the craniolateral surface to the caudal surface, or towards the tail of the horse.
• The principal tensile strain of the tibia was observed just to the lateral side of the cranial aspect, in both the proximal and diaphyseal regions. This indicates a tension directed slightly to the side of the horse’s head.
• As with the radius, the largest strains in the distal tibia were torsional, and the application of a cast modified the major tension axis.
• Unlike with the radius, however, the cast did not decrease the strains’ magnitude measured on the tibia.

Implications for fracture stabilization

• The study concludes that casts might not be effective in stabilizing fractures of the radius and tibia in equines, according to the strain distribution observed.
• Even though they altered the direction of the main tensile strain, they did not reduce the absolute coordinates of the strains measured.
• The research suggests that casts may even add additional stress to the fracture site, posing a potential risk to bone repair.