An in vitro biomechanical investigation of an MP35N intramedullary interlocking nail system for repair of third metacarpal fractures in adult horses.

This research study explored the mechanical properties of horse metacarpal bones (MC3) repaired with an MP35N interlocking nail system, comparing it to normal, unbroken bones. The findings suggest that while the repaired bones were less stiff and strong than intact bones, the repairing system was satisfactory to endure the in vivo forces experienced by horses’ legs and could be considered a viable treatment option for MC3 fractures.

Research Methodology

The researchers conducted their investigation on cadaveric equine MC3 bones:

• Twenty-four pairs of these bones were used in the study.
• Each pair was divided into four groups (six pairs per group) dedicated for different mechanical stress tests: compression, bending in different directions (palmarodorsal and mediolateral), and torsion.
• In each pair, one bone was left as an intact specimen while the other was intentionally damaged and repaired with an MP35N interlocking nail system.
• The damages were done by gap ostectomy, a surgical procedure to create a space in the bone, and stabilized with a 4-hole, 14-mm-diameter, 250-mm-long, MP35N intramedullary nail, and four, 7-mm-diameter, 60-mm-long MP35N interlocking screws.

Results

• The intact specimens were found to be significantly stronger and stiffer than the repaired counterparts in all testing conditions except in palmarodorsal bending.
• However, the repaired specimens demonstrated sufficient resilience against the forces exerted during the tests. They achieved mean yield strengths that were 57% for compression, 81% for palmarodorsal bending, 68% for mediolateral bending, and 78% for torsion, in relation to the intact specimens.
• Additionally, the repaired specimens achieved mean stiffnesses that were 53% for compression, 58% for palmarodorsal bending, 41% for mediolateral bending, and 47% for torsion, in contrast to the intact specimens.

Conclusions

• On the whole, the study concludes that while repaired MC3 bones show comparatively lower mechanical properties than intact bones, they still surpassed the reported in vivo loads for dorsopalmar bending and compression, as well as the estimated in vivo torsional loads.
• Therefore, an MP35N interlocking nail system shows promise as a feasible technique for the repair of MC3 fractures in horses, providing adequate strength and stability post-surgery. It is particularly recommended for fractures with applicable configurations that are best suitable for such a repair approach.