Effect of sequential removal of parts of the second metacarpal bone on the biomechanical stability of the equine carpus.
Authors: Seabaugh Kathryn A, Hubert Jeremy D, Kawcak Christopher E, McGilvray Kirk C, Santoni Brandon G, Rao Sangeeta, Baxter Gary M
Journal: Veterinary surgery : VS
Summary
# Editorial Summary Removal of the second metacarpal bone (MC2) is occasionally considered for managing MC2 fractures or degenerative disease, yet little evidence exists regarding its biomechanical consequences for carpal function. Researchers subjected 16 cadaveric equine forelimbs to axial compression and combined compression-torsion testing, progressively removing 50%, 80%, and finally 100% of MC2 to measure changes in carpal stiffness and intercarpal motion. Complete MC2 resection resulted in significantly reduced torsional stiffness—the carpus became notably less able to resist twisting forces—whilst axial (vertical) compressive stiffness remained unchanged; additionally, rotational movement around the long axis increased substantially between the second and third carpal bones and between the second carpal bone and third metacarpal when MC2 was entirely absent, but not when only partial removal occurred. These findings suggest that partial MC2 resection may preserve adequate biomechanical stability for weight-bearing, whereas complete resection compromises the carpus's ability to manage torsional loads—a critical consideration when assessing surgical outcomes and long-term soundness in horses undergoing this procedure.
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Practical Takeaways
- •Partial MC2 lesions (50–80% bone loss) maintain adequate torsional stability in the carpus, suggesting horses may tolerate incomplete fractures or partial bone loss relatively well
- •Complete MC2 loss dramatically reduces the carpus's ability to resist rotational forces, which may explain clinical instability and lameness in cases of full-thickness fractures or complete osteochondrosis
- •This biomechanical data supports conservative management of incomplete MC2 lesions, but indicates surgical stabilisation or complete fracture union is critical to prevent functional carpal instability
Key Findings
- •Complete removal of MC2 significantly decreased compressive + torsional stiffness of the carpus, but axial compressive stiffness remained unchanged
- •100% MC2 removal caused significant increase in rotational motion around the long axis between the second carpal bone and third metacarpal/third carpal bones compared to 50% and 80% removal
- •Torsional stability of the equine carpus is significantly compromised only after complete MC2 resection, not with partial removal