In vitro comparison of the effect of parallel and divergent transfixation pins on breaking strength of equine third metacarpal bones.

This research studies the breaking strength of horse metacarpal bones with transfixation pins placed in two different configurations – parallel and 30 degrees divergent. The outcome revealed that bones with divergent pins had significantly more strength than those with parallel pins.

Research Objective

The overall goal of the study was to examine the breaking strength (the torque at the point of failure) of equine third metacarpal (leg) bones with two different placements of transfixation pins – parallel to each other and 30 degrees divergent from each other. This was done in an in vitro environment to afford absolute control over experimental variables.

• The transfixation pins are commonly used in orthopedic surgeries to stabilize fractures.
• The breaking strength determines the amount of torque or twisting force required to break the bone – an indication of bone strength.

Methodology

The team used the third metacarpal bones from the forelegs of 12 horses for the study. These bones were paired and two transfixation pin holes were made in the distal metaphysis (end portion of the bone before the joint) in the assigned configuration with the aid of a specially created jig.

• The bones were then tested deliberately in torsion (twisting) to measure the force at which they failed.
• By doing so, the researchers were able to calculate the torque at the point of failure for each set of bones and compare it based on limb and pin configuration.

Findings

The study found a significant difference in the breaking strength between the two pin configurations tested.

• Bones with pins in a divergent configuration were found to be significantly stronger than those with parallel pins.
• The fractures achieved during testing also differed based on the pin configuration. In bones with parallel pins, the fractures were longitudinal oblique and propagated from a singular bone-pin interface; whereas bones with divergent pins displayed more comminuted (fragmented) fractures from multiple bone-pin interfaces.

The results from this research could potentially change surgical practices when placing fixation pins in equine orthopedic surgeries. It suggests that divergent placement of the pins significantly improves the strength of the repair.