Comparison of 3.5- and 4.0-mm Cortical Bone Screws for Stabilization of an Equine Navicular Bone Fracture Model
Authors: G. Stucki, S. Valet, A. Fuerst, B. Weisse, M. A. Jackson
Journal: Veterinary and Comparative Orthopaedics and Traumatology
Summary
Navicular bone fractures in horses present a significant orthopaedic challenge, particularly given the demanding biomechanical environment of the distal limb; this in vitro study compared two commonly available cortical screw diameters (3.5 mm and 4.0 mm) to establish which offers superior stabilisation in fracture repair models. Using a four-point bending apparatus, researchers subjected screw–bone constructs to both static loading until failure and cyclic loading protocols, measuring ultimate load-bearing capacity and fatigue resistance. The 4.0-mm screws demonstrated a clinically meaningful 16% increase in static strength compared with 3.5-mm constructs (p = 0.0135), though no statistically significant difference emerged in cyclic testing—a finding attributable to substantial variability in fatigue data rather than true equivalence between groups. For practitioners managing navicular fractures surgically, the superior static load capacity of 4.0-mm screws suggests potential advantages in reducing construct failure risk, particularly in heavier horses or those with early return to work; however, the authors appropriately note that in vivo validation is essential before recommending a wholesale shift in implant selection, as insertion complexity and potential complications in live bone must be evaluated clinically.
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Practical Takeaways
- •The 4.0-mm cortical screw shows superior static strength characteristics and may provide better fracture stability for navicular bone repairs, but clinical validation is still needed before widespread adoption
- •High variability in cyclic loading performance suggests screw size alone may not be the only factor affecting long-term implant durability—other variables like bone quality and surgical technique warrant investigation
- •Before switching implant sizes in practice, await clinical studies confirming that 4.0-mm screws can be reliably inserted without iatrogenic damage to the small navicular bone
Key Findings
- •4.0-mm cortical screws demonstrated 16% greater load at failure compared to 3.5-mm screws in static testing (p=0.0135)
- •No significant difference in cycles to failure between 4.0-mm and 3.5-mm constructs in cyclic loading testing due to high variability
- •4.0-mm cortical screws offer biomechanical advantages for navicular bone fracture stabilization in an in vitro model