Influence of screw head diameter on ex vivo fixation of equine lateral condylar fractures with 5.5 mm cortical screws.
Authors: Constant Caroline, Zderic Ivan, Arens Daniel, Pugliese Brenna, Gehweiler Dominic, Gueorguiev-Rüegg Boyko, Zeiter Stephan
Journal: Veterinary surgery : VS
Summary
# Lateral Condylar Fractures in Equine Metacarpal Bones: Does Screw Head Diameter Matter? Lateral condylar fractures of the third metacarpal bone represent a significant clinical challenge in equine orthopaedics, and optimising fixation constructs is essential for achieving union and return to function. Constant and colleagues conducted a controlled ex vivo biomechanical study using 15 pairs of equine MC3 bones with simulated parasagittal osteotomies, comparing fixation with standard 5.5 mm cortical screws (8 mm head diameter) against modified variants with 10 mm heads, testing constructs under insertion torque, quasi-static axial loading, and cyclic loading protocols. The larger-headed screws permitted significantly greater insertion torque (8.1 vs 7.4 Nm) and demonstrated substantially higher axial failure loads—approximately 1.4 times greater (12,347 vs 8,695 N)—alongside improved yield characteristics, though cyclic loading behaviour to 2 mm displacement showed no meaningful difference between groups. These findings suggest that increasing screw head diameter enhances the mechanical stability of lateral condylar repairs under loading conditions relevant to early post-operative weightbearing, potentially reducing the risk of construct failure during the critical healing phase, though clinical validation in living horses remains necessary before recommending routine adoption in practice.
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Practical Takeaways
- •Modified 5.5 mm cortical screws with larger (10 mm) heads provide superior fixation strength for equine condylar fractures and should be considered for clinical use in fracture repair cases
- •The improved resistance to axial loading and insertion torque with larger-head screws may reduce healing complications and increase construct reliability during recovery
- •Cyclic loading performance was equivalent between screw types, suggesting improved static strength does not compromise fatigue characteristics
Key Findings
- •Modified 5.5 mm cortical screws with 10 mm heads achieved greater maximum insertion torque (8.1 vs 7.4 Nm) compared to standard 8 mm head screws
- •Modified screws demonstrated 1.4-fold greater quasi-static failure loads (12,347 vs 8,695 N)
- •Axial yield load was significantly higher with modified screws (7,118 vs 5,740 N)
- •No difference detected between screw types in fatigue resistance to 2 mm displacement under cyclic loading