Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of three 4.5-mm and two 5.5-mm cortical screws.
Authors: Watt B C, Edwards R B, Markel M D, McCabe R, Wilson D G
Journal: Veterinary surgery : VS
Summary
# Editorial Summary Proximal interphalangeal (pastern) joint arthrodesis remains a common surgical intervention for horses with severe degenerative joint disease, but optimal fixation technique remains debated. Watt and colleagues conducted a biomechanical comparison of two established parallel-screw configurations using cadaveric equine limbs: three 4.5-mm cortical screws versus two 5.5-mm cortical screws, both placed in lag fashion. Under 3-point bending loads simulating dorsal-to-palmar/plantar forces, the two techniques demonstrated equivalent maximal bending moments and composite stiffness, though front limbs generally tolerated higher loads than hind limbs before failure occurred. Notably, more individual 4.5-mm screws fractured compared to 5.5-mm screws, suggesting larger-diameter implants may offer improved durability despite similar overall construct performance. For practitioners, these findings support use of the biomechanically simpler two 5.5-mm screw technique without sacrificing structural integrity, reducing operative time and implant costs whilst maintaining comparable load-bearing capacity in the critical early healing phase.
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Practical Takeaways
- •Use two 5.5-mm screws instead of three 4.5-mm screws for pastern arthrodesis—it's simpler surgery with identical biomechanical strength
- •Front limbs tolerate higher loads than hind limbs in pastern arthrodesis, which may inform postoperative exercise recommendations
- •Larger diameter screws (5.5-mm) are more durable than smaller ones; consider this when selecting implants for demanding cases
Key Findings
- •No significant difference in bending moment at failure between three 4.5-mm screws and two 5.5-mm screws (P >0.05)
- •No significant difference in composite stiffness between fixation techniques (P >0.05)
- •Front limbs demonstrated higher maximal bending moment at failure than hind limbs
- •Greater number of 4.5-mm cortical screws failed compared to 5.5-mm cortical screws