Mechanical Effects of Off-Axis Insertion of Locking Screws - Should we do it?
Journal of Orthopaedic Trauma, Publish Ahead of Print():-, 2014
Cartner JL, Petteys T, Tornetta P
Objectives: The purposes of this study were to evaluate the cantilevered bending strength and failure modes of locking screws inserted at various angles in a plate with fully circumferential threaded holes. As an additional measure, the amount of screw head prominence at these angles was also assessed.
Methods: Standard 3.5 mm locking screws were inserted into round fully circumferential threaded holes through a standard straight 3.5 mm locking plate at various angles. The achieved angle of insertion and its prominence protruding from the far-bone side of the plate was measured using an optical luminescence technique. Each screw was then loaded at a constant rate until failure in a cantilevered bending scenario. The maximum cantilevered bending strength was measured and the moment at failure was calculated.
Results: There was a positive correlation between increasing insertion angle and increasing prominence; a higher screw insertion angle yielded greater prominence. Prominence values ranged from negligible up to 2 mm. As screw insertion angle increased, the bending moment at failure decreased. Screws inserted to 3-degrees or below primarily failed via screw deformation at the minor diameter below the head, whereas screws inserted to greater than 3-degrees primarily failed via locking mechanism disengagement.
Conclusions: These findings indicate that cross-threading may not be biomechanically advantageous and change screw mode of failure. Based on these findings, screws inserted to 3-degrees or higher would reduce the bending moment at failure to approximately 50% of an orthogonally inserted screw.
Cartner JL, Petteys T, Tornetta P
Objectives: The purposes of this study were to evaluate the cantilevered bending strength and failure modes of locking screws inserted at various angles in a plate with fully circumferential threaded holes. As an additional measure, the amount of screw head prominence at these angles was also assessed.
Methods: Standard 3.5 mm locking screws were inserted into round fully circumferential threaded holes through a standard straight 3.5 mm locking plate at various angles. The achieved angle of insertion and its prominence protruding from the far-bone side of the plate was measured using an optical luminescence technique. Each screw was then loaded at a constant rate until failure in a cantilevered bending scenario. The maximum cantilevered bending strength was measured and the moment at failure was calculated.
Results: There was a positive correlation between increasing insertion angle and increasing prominence; a higher screw insertion angle yielded greater prominence. Prominence values ranged from negligible up to 2 mm. As screw insertion angle increased, the bending moment at failure decreased. Screws inserted to 3-degrees or below primarily failed via screw deformation at the minor diameter below the head, whereas screws inserted to greater than 3-degrees primarily failed via locking mechanism disengagement.
Conclusions: These findings indicate that cross-threading may not be biomechanically advantageous and change screw mode of failure. Based on these findings, screws inserted to 3-degrees or higher would reduce the bending moment at failure to approximately 50% of an orthogonally inserted screw.
No hay comentarios:
Publicar un comentario