Comparison of insertion time and pullout strength between self-tapping and non-self-tapping AO 4.5-mm cortical bone screws in adult equine third metacarpal bone.
Authors: Andrea C Renee, Stover Susan M, Galuppo Larry D, Taylor Ken T, Rakestraw Peter C
Journal: Veterinary surgery : VS
Summary
# Editorial Summary When stabilising third metacarpal (MC3) fractures in adult horses, surgeons must balance mechanical reliability against surgical efficiency, and this 2002 biomechanical study directly addresses that trade-off for AO 4.5-mm cortical screws. Researchers tested self-tapping (ST) and non-self-tapping (NST) screws inserted bicortically across proximal, middle, and distal regions of paired equine MC3 bones, measuring insertion time, torque requirements, and pullout strength under mechanical testing. Whilst ST screws took considerably longer to insert individually, the total procedural time favoured ST screws by more than 50% because NST screws required separate pre-tapping—a substantial practical advantage in the operating theatre. Most critically, both screw types demonstrated equivalent pullout mechanical properties (stiffness, strength, and failure load), negating any mechanical disadvantage to choosing the faster option. However, the findings warrant caution: bone failure and comminution were more frequently associated with ST screws during pullout testing, suggesting that whilst insertion time is dramatically reduced, surgeons should carefully assess bone quality and screw placement to avoid stress concentration at the implant site. For practitioners repairing MC3 fractures in adult horses, ST screws offer genuine time savings without sacrificing fixation strength, though meticulous attention to insertion technique remains essential to minimise the risk of iatrogenic bone damage.
Read the full abstract on PubMed
Practical Takeaways
- •Self-tapping 4.5-mm cortical screws offer substantial time savings in surgical application for MC3 fracture repair without compromising holding strength, making them practical for clinical use
- •Surgeons should monitor for bone comminution and failure at self-tapping screw sites, as these failures occurred more frequently than with non-self-tapping screws despite equivalent pullout strength
- •Diaphyseal screw placement provides biomechanically superior fixation compared to metaphyseal locations when treating MC3 fractures
Key Findings
- •Self-tapping screws required significantly less total insertion time (less than half) compared to non-self-tapping screws with pre-tapping
- •No statistically significant differences in pullout mechanical properties (strength, stiffness) were observed between self-tapping and non-self-tapping screws
- •Diaphyseal locations demonstrated significantly stiffer and stronger structure than metaphyseal locations
- •Screw breakage was the more common pullout failure mode, though bone failure occurred more frequently with self-tapping screws