Axial compression generated by cortical and cancellous lag screws in the equine distal phalanx.

The research investigates how the use of larger diameter screws in repairing equine distal phalanx fractures can potentially increase axial compression and improve fracture stability. The study found that a 6.5mm screw, inserted after pre-tapping, generated significantly more axial force than smaller screws, suggesting improved fracture compression.

Objective and Hypothesis

• The researchers were attempting to address the challenges in using screw fixation as a technique for repairing mid-sagittal plane fractures of the distal phalanx in adult horses. There are concerns with this method related to implant infections and achieving adequate interfragmentary compression. The researchers hypothesized that using larger diameter screws could increase axial compression and enhance the stability of the fracture.

Methodology

• The study involved distal phalanges collected from the forelimbs of ten adult horses post-mortem. They cut these in half in the midsagittal plane.
• They used a randomized block study design and tested four types of bone screws (4.5 mm cortical, 5.5 mm cortical, 6.5 mm cancellous pre-tapped, and 6.5 mm cancellous non-tapped). The screws were inserted to a depth of 15 mm.
• They measured the axial force generated under the screw head using a load washer containing a piezoelectric force transducer. They recorded the torque during screw insertion using a torsional testing machine.

Findings

• The 6.5mm screw inserted after pre-tapping generated significantly greater axial force (2781 N) in comparison to the 4.5 mm (1522 N), 5.5 mm (2073 N), or 6.5 mm non-tapped (2295 N) screws.
• The relationship between the maximum applied torque and the generated axial force was linear for each screw type. Every unit of torque applied during the insertion of cortical screws resulted in a greater increase in axial compression, in comparison to cancellous screws.

Conclusion

• These findings suggest that using larger diameter screws could potentially result in improved interfragmentary compression of distal phalangeal fractures, enhancing the efficacy of the repair technique. This could help address the common concerns in using screw fixation for equine distal phalanx repairs.