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BIOMECHANICAL ANALYSIS OF ORTHOGONAL AND UNILATERAL LOCKING PLATE CONSTRUCTS IN A FRACTURE GAP MODEL
Thesis

BIOMECHANICAL ANALYSIS OF ORTHOGONAL AND UNILATERAL LOCKING PLATE CONSTRUCTS IN A FRACTURE GAP MODEL

Peter James Welsh
Washington State University
Master of Science (MS), Washington State University
07/2025
DOI:
https://doi.org/10.7273/000008008
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Abstract

axial compression bone plate fracture gap fracture repair implant failure Orthopedic biomechanics Translation studies
Objective: The primary aim of this study was to compare unilaterally plated (UP) constructs and orthogonally plated (OP) constructs of differing sizes (3.5 mm + 2.0 mm locking plates [OP2.0], 3.5 mm + 2.4 mm locking plates [OP2.4] and 3.5 mm + 3.0 mm locking plates [OP3.0]) under cyclic and static axial compression load to failure testing using a fracture gap model. The secondary aim was to evaluate the effect of cyclic loading on load to failure testing and to determine if increasing the overall strength and stiffness of the construct by adding orthogonal plates has an effect on cyclic fatigue strength and stiffness when compared to non-fatigued constructs. Study design: In vitro experimental biomechanical study. Sample population: Acetal homopolymer (Delrin) rods stabilized with locking plates and screws (Arthrex OrthoLine™). Methods: One of four stabilization techniques (UP, OP2.0, OP2.4, OP3.0) was applied to rods with a fixed fracture gap. Constructs were divided into two groups, fatigued and non-fatigued. Fatigued constructs were cycled under axial compression (90,000 cycles; 4–196 N) followed by static load to failure. Cyclic displacement was evaluated after the first, middle, and last 100 cycles. Non-fatigued groups solely subjected to static axial compression load to failure. Stiffness and strength were analyzed during static axial compression load to failure. Results: During cyclic testing, UP experienced 3.5, 3.8, and 4.1 times the gap strain of OP2.0, OP2.4, and OP3.0, respectively (p < 0.0075). Fatigue and construct design had significant effects on displacement (p < .0001). OP2.0, OP2.4, and OP3.0 demonstrated 2.5, 3.0, and 4.1 times the strength and 3.0, 3.6, and 4.2 times the stiffness of UP, respectively (p < .0002). There was no difference in strength (p = 0.5388) or stiffness (p = 0.3391) between fatigued and non-fatigued groups. Conclusion: In the present in vitro fracture gap model, OP constructs were stronger and stiffer than UP under dynamic and static axial compression, and OP stiffness increased with increasing implant size. Despite biomechanical advantages of OP constructs when compared to UP, fatigued and non-fatigued groups had no difference in strength and stiffness. Increasing overall construct strength and stiffness also had no effect on fatigue resistance. Clinical significance: The results of this study demonstrate objective biomechanical advantages of OP compared to UP. Moreover, these results demonstrate that increasing the strength and stiffness of a construct by adding an orthogonal plate did not significantly increase resistance to fatigue. Based on these results, orthogonal plating can be considered when increased fixation strength and stiffness are warranted.

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