A biomechanical comparison of equine third metacarpal condylar bone fragment compression and screw pushout strength between headless tapered variable pitch and AO cortical bone screws.
Authors: Galuppo Larry D, Stover Susan M, Jensen David G
Journal: Veterinary surgery : VS
Summary
# Editorial Summary Lateral condylar fractures of the equine third metacarpal remain a significant orthopaedic challenge, and the choice of internal fixation hardware directly influences clinical outcomes. Galuppo and colleagues conducted an in vitro biomechanical study comparing two screw systems—the 6.5-mm Acutrak Plus (headless tapered variable pitch) and 4.5-mm AO cortical screws—using cadaveric equine metacarpi stabilised with a simulated complete lateral condylar fracture model. The 4.5-mm AO screws generated substantially greater interfragmentary compression, producing 65% more compressive pressure and 44% more compressive force than the Acutrak Plus screws, yet both screw types demonstrated similar pushout stiffness and comparable bone-holding capacity when cyclically loaded to failure. Paradoxically, the 6.5-mm Acutrak Plus screws actually showed superior pushout strength despite producing less interfragmentary compression—a finding suggesting that screw diameter and design geometry may compensate for reduced compression force in resisting pull-out. For practitioners selecting fixation methods for condylar fractures, this research indicates that whilst AO screws offer superior compression characteristics to promote fracture healing, Acutrak Plus screws provide adequate mechanical holding strength; the clinical choice should therefore weigh the importance of initial interfragmentary compression against the mechanical advantages each system provides during the weight-bearing rehabilitation phase.
Read the full abstract on PubMed
Practical Takeaways
- •AP screws may be clinically appropriate for condylar fracture fixation where maximum interfragmentary compression is not the primary concern, as they provide adequate pushout strength despite lower initial compression
- •If achieving maximum initial fragment compression is critical to your surgical outcome, AO screws deliver superior compressive force during insertion, though this advantage must be weighed against AP screw's superior resistance to pullout
- •Screw selection should consider both insertion torque requirements (lower for AP) and final holding strength (higher for AP), allowing surgeons to match implant choice to fracture pattern and bone quality in individual cases
Key Findings
- •Acutrak Plus (AP) screws generated only 65% of the compressive pressure and 44% of compressive force compared to AO cortical screws during insertion
- •AP screws demonstrated greater pushout strength than AO screws despite lower initial fragment compression
- •Pushout stiffness was similar between both screw types, indicating comparable mechanical stability post-insertion
- •AO screws required significantly greater insertion torque than AP screws during tapping and insertion phases