Biomechanical Comparison of a Headless Compression Screw Fastener and AO Cortical Bone Screw for Fixation of a Simulated Equine Third Carpal Bone Slab Fracture.

The research article studies the application of a new type of compression screw fastener, the Headless Compression Screw Fastener (HCSF), in treating frontal plane slab fractures of the third carpal bone (C3) in horsed compared to the conventional AO cortical bone screw. The findings suggest no significant difference in terms of maximum load to failure, stiffness or yield load, however, the HCSF shows advantages in its design and invites further clinical investigations.

Research Context and Purpose

• The bone fracture under scrutiny is the third carpal bone (C3) frontal plane slab fracture, commonly occurring in racing and performance horses. The prevailing treatment method is stabilization with a lagged AO cortical screw.
• However, conventional AO screws can cause complications such as fragment splitting, fragment spinning, and irritation of the dorsal soft tissue structures.
• To overcome these issues, a novel Headless Compression Screw Fastener (HCSF) has been introduced. The HCSF has interlocking threads that can resist multidirectional forces and bending moments.
• The research aims to compare the biomechanical performance of these two types of screws in equine C3 fractures.

Research Methodology

• Frontal plane slab fractures of C3 were simulated on pairs of carpi from nine equine cadaver limbs and were fixed using either the HCSF or AO cortical screw.
• The repaired structures were subjected to shear stress until failure, and the effects of screw type on stiffness, maximum load to failure, and yield load were analyzed.
• Linear mixed models were used to perform the analysis. It should be noted that all failures were due to screw bending.

Research Findings and Conclusion

• The analysis found no significant difference between the two screw types concerning maximum load to failure, stiffness, or yield load.
• However, the HCSF was effective in compressing the fracture owing to its different head and thread pitches. Furthermore, the headless design of the HCSF negates the need for counter-sinking.
• Although some failures were associated with the sagittal fracture at the screw-bone interface in both groups, the HCSF was successfully used to repair the simulated fractures.
• The research concludes that due to the performance and added benefits of the HCSF, it invites further clinical investigations and applications for treating C3 fractures in horses.