An in vitro biomechanical investigation of an MP35N intramedullary interlocking nail system for repair of third metacarpal fractures in adult horses.
Authors: Galuppo Larry D, Stover Susan M, Aldridge Amanda, Hewes Christina, Taylor Kenneth T
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: MP35N Interlocking Nail Fixation for Equine Third Metacarpal Fractures Fracture repair in the equine third metacarpal bone (MC3) demands fixation methods capable of withstanding substantial and multidirectional loading forces during rehabilitation and return to work. Researchers subjected 24 pairs of cadaveric MC3 bones to mechanical testing across four loading modes—compression, palmarodorsal and mediolateral bending, and torsion—comparing intact bones with those gap-ostectomized and stabilised using a 14-mm MP35N intramedullary nail with four 7-mm interlocking screws. The constructs demonstrated significantly reduced strength and stiffness across most loading modes, achieving only 53–81% of intact bone yield strength and 41–58% of stiffness depending on the direction of force applied. Critically, however, the constructs' mechanical properties exceeded both documented in vivo loading forces during normal locomotion and estimated torsional loads that the limb experiences functionally. These findings suggest that whilst MP35N interlocking nail fixation does not restore intact bone biomechanics, the system provides sufficient load-bearing capacity for clinical fracture repair in MC3 bones with appropriate fracture configurations, supporting its consideration as a viable surgical option alongside traditional repair methods.
Read the full abstract on PubMed
Practical Takeaways
- •The MP35N interlocking nail can safely stabilize third metacarpal fractures because construct strength exceeds the actual forces these bones experience during normal loading
- •Mediolateral bending represents the weakest point of this fixation system—be cautious with lateral-impact injuries or horses returning to work too quickly
- •This system is a viable option for metacarpal fractures with suitable configuration, offering an alternative to plate fixation or external devices
Key Findings
- •MP35N interlocking nail constructs achieved 57-81% of intact bone yield strength across compression, bending, and torsional loading modes
- •Constructs demonstrated lower stiffness than intact bones (41-58% of intact values), with mediolateral bending showing the greatest weakness
- •Yield strengths in dorsopalmar bending (81%) and compression (57%) exceeded reported in vivo physiological loads on equine third metacarpal bones
- •MP35N interlocking nail system provided adequate mechanical stability for fracture repair in applicable configurations despite being weaker than intact bone