An in vitro biomechanical comparison of an interlocking nail system and dynamic compression plate fixation of ostectomized equine third metacarpal bones.

This study compared two methods of stabilizing a surgically cut (ostectomized) horse’s third metacarpal bone: (1) the interlocking nail system, and (2) the double dynamic compression plate technique. The results showed that while both techniques had similar performance in bending tests, the double plating method was superior in resistance to twisting or torsion.

Research Methodology

• The research involved ten pairs of adult horse forelimbs. The third metacarpal bones (MC3) from these limbs were divided into two groups for testing: one examined the bones’ response to bending (caudocranial four-point bending), while the other measured twisting or torsion resistance.
• In each group, one bone was fixed with interlocking nails, while the contralateral bone was fitted with two dynamic compression plates, one dorsally and one laterally. All bones underwent mid-diaphyseal ostectomies, a surgical procedure where a segment of the bone is removed.
• Each construct was subjected to specific tests to measure rigidity, the bending moment at which deformation starts (yield bending moment), and the bending moment at which the construct fails (failure bending moment).
• These results were then compared within each pair using a statistical technique known as paired T-test to find if any significant difference existed between the performances of the two fixation methods. The threshold for statistical significance was set at P<.05.

Results

• In the context of bending, both the interlocking nail and double plating techniques displayed similar performances. There was no significant difference in composite rigidity, yield bending moment, and failure bending moment between the two.
• However, in torsion tests, the double plating technique was significantly superior. It outperformed the interlocking nail system in terms of composite rigidity, gap stiffness (a measure of how a bone can resist deformation when subjected to torsional forces), and yield load (the torque at which deformation commences).

Conclusions

• The study concluded that both fixation methods — the interlocking nail system and the double dynamic compression plate technique — are equally effective in terms of their biomechanical properties when subjected to bending forces.
• However, when it comes to torsion, the double plating technique is markedly more effective than the interlocking nail system in stabilizing ostectomized equine MC3. It offered higher composite rigidity, gap stiffness, and yield load, making it the preferred option for situations where resistance to twisting is crucial.