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Biomechanical comparison of bicortical locking versus unicortical far-cortex-abutting locking screw-plate fixation
Steven J Overturf1, Randal P Morris1, Zbigniew Gugala1
1Department of Orthopaedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, TX.
Purpose:
To provide comparative biomechanical evaluation of bicortical locking versus unicortical-abutting locking screw-plate fixation in a comminuted radius fracture model.
Methods:
A validated synthetic substitute of the adult human radius with a 1.5-cm-long segmental mid-diaphyseal defect was used in the study to simulate a comminuted fracture. Stabilization was achieved with an 8-hole locking plate and either bicortical screws or unicortical-abutting screws. The specimens were tested using nondestructive cyclical loading in 4-point bending, axial compression, and torsion to determine stiffness and displacement and subsequently in 4-point bending to assess load to failure.
Results:
There were no statistically significant differences between bicortical versus unicortical-abutting locking screw fixation in nondestructive 4-point bending, axial compression, and torsion. Both locking screw constructs also demonstrated comparable 4-point bending loads to failure.
Conclusion:
The biomechanical equivalence between bicortical locking versus unicortical-abutting locking screw-plate fixation suggests that adequate locking plate fixation can be achieved without perforation of the far cortex. The abutment of the screw tip within the far cortex enhances the unicortical screw positional stability and thereby effectively opposes the displacement of the screw when subjected to bending or axial or rotational loads.
Clinical Relevance:
Unicortical-abutting screws potentially offer several clinical advantages. They eliminate the need for drilling through the far cortex and thereby a risk of adjacent neurovascular injury or soft tissue structure compromise. They eliminate the issues associated with symptomatic screw prominence. They can decrease risk of refracture after screw-plate removal. In case of revision plating, they permit conversion to bicortical locking screws through the same near-cortex screw holes, which eliminates the need for a longer or repositioned plate.
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