Axial compression generated by cortical and cancellous lag screws in the equine distal phalanx.
Authors: Johnson K A, Smith F W
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Axial Compression in Equine Distal Phalanx Fixation Mid-sagittal fractures of the distal phalanx in horses have traditionally been repaired using single 4.5 mm cortical lag screws, yet surgeons frequently encounter challenges achieving adequate interfragmentary compression and managing implant-related complications. Johnson and Smith tested whether larger-diameter screws could generate superior compression forces by inserting four screw types (4.5 mm cortical, 5.5 mm cortical, 6.5 mm cancellous pre-tapped, and 6.5 mm cancellous non-tapped) into paired mid-sagittally divided distal phalanges from ten horses, measuring axial force beneath the screw head during insertion and recording insertion torque. The 6.5 mm pre-tapped cancellous screw produced significantly greater axial compression (2781 N) compared with the standard 4.5 mm cortical screw (1522 N), whilst cortical screws demonstrated a more efficient torque-to-compression ratio than their cancellous counterparts. These findings suggest that upgrading to larger-diameter screws—particularly 6.5 mm pre-tapped cancellous options—could enhance interfragmentary stability and potentially reduce the technical difficulties and infection risk associated with conventional mid-phalanx fracture repair.
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Practical Takeaways
- •Consider using 6.5 mm pre-tapped cancellous screws instead of standard 4.5 mm cortical screws for distal phalanx fractures to achieve superior compression and potentially more stable repairs
- •Pre-tapping technique matters significantly—pre-tapped 6.5 mm cancellous screws outperformed non-tapped versions by 21%, suggesting proper surgical preparation is critical
- •Surgeons should monitor insertion torque as a practical guide to achieving adequate compression, since torque directly correlates with axial force generation
Key Findings
- •6.5 mm pre-tapped cancellous screws generated significantly greater axial force (2781 N) compared to 4.5 mm cortical (1522 N), 5.5 mm cortical (2073 N), and 6.5 mm non-tapped cancellous (2295 N) screws
- •A linear relationship exists between maximal applied torque and axial force generated for each screw type
- •Cortical screws produced greater axial compression per unit of torque applied during insertion compared to cancellous screws
- •Larger diameter screws improved interfragmentary compression in distal phalangeal fracture models