An in vitro biomechanical investigation of an equine interlocking nail.

This research study investigates the mechanical properties of an Equine Interlocking Nail (EIN) used in horse tibia surgery, comparing the in vitro test results with estimated in vivo loads. The results demonstrate that the EIN’s torsional yield strength is insufficient to provide stability in real-life conditions, suggesting further modifications are needed for this method of fracture repair.

Research Methodology

• The study employed in vitro biomechanical investigation to measure the mechanical properties of the EIN.
• The experiment was conducted using twelve adult tibiae from horse cadavers. Osteotomized tibiae were stabilized using the EIN and tested.
• Each EIN-stabilized tibia was tested under different conditions: compression, 3-point bending, 4-point bending, and torsion. Each of these tests is designed to simulate the different types of forces a horse’s leg might experience in the real world.

Research Results

• The results of the tests showed that the mean compressive yield load and bending moment of the EIN-tibial composite were greater than the loads expected postoperatively in vivo. This means that the EIN was stronger than needed under compression and bending forces.
• However, the testing results revealed that the mean torsional yield load was less than that expected in vivo. This suggests that the EIN is not strong enough to withstand the torsional forces a horse’s leg would experience, particularly during walking.
• These findings imply that while the EIN can withstand the loads exerted by compressive and bending forces, it fails to provide sufficient torsional (twisting) strength. Consequently, the EIN may lack the necessary stability for walking in adult horses.

Conclusions and Implications

• Given its low torsional yield strength, the EIN is currently an unsuitable method for tibial fracture repair in adult horses. The results indicate that the EIN’s mechanical properties may not withstand the postoperative torsional loads encountered during walking.
• Nevertheless, the potential biological advantages offered by this method of fracture repair warrant further investigation and modification of the interlocking nail design. Future development could render this method more effective for treating adult equine tibial fractures.