Comparative Biomechanical Analysis of Six Orthopedic Fixation Constructs Under Cyclic Loading

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Abstract

ABSTRACT Fixation constructs used in orthopedic surgery are typically evaluated based on their initial mechanical strength. However, fixation failure often occurs under cyclic loading in dynamic environments where early motion and stress concentration are common. In the foot and ankle, nitonal staples and short locking plates have been developed to maximize construct stiffness and accommodate the limited bony surface area available for fixation. The implants have grown in popularity, but unlike other AO constructs, they have not been rigorously studied across multiple mechanical performance domains. Prior studies have not comprehensively compared dynamic nitinol constructs to static plates and screws across key mechanical performance metrics under fatigue conditions. Six fixation constructs (2‐leg staple, 4‐leg staple, 4‐leg + 2‐leg perpendicular staple, 4‐hole titanium plate, 5‐hole titanium plate with cross‐screw, and 4‐leg staple + dynamic disc + cross‐screw) were evaluated using standardized synthetic bone block models ( n  = 5/group). Constructs were subjected to 100 cycles of loading. Pre‐ and post‐cycle values for compression ( N ), contact area (mm²), rigidity ( N ), and torque ( N ·cm) were measured. Paired t‐tests assessed intra‐construct degradation as well as post‐cycle inter‐construct differences. Additionally, ANOVA with Tukey HSD identified inter‐construct differences in degradation. Cohen's d quantified effect sizes. The 4‐leg + 2‐leg perpendicular construct had the highest post‐cycle compression (68.0 N) and contact area (447.2 mm²), with small to moderate degradation (d = –1.38; −0.99); the 4‐hole plate showed the greatest degradation ( p  = 0.001, d = −3.48; p  < 0.001, d = −4.45). Torque and rigidity degraded most in the 5‐hole plate (Δ = −94.4 N·cm, p  = 0.0002, d = −6.21; Δ = −237.4 N, p  = 0.015, d = −1.83), while dynamic constructs showed better retention. Dynamic nitinol constructs outperformed static plates and screws across all metrics, especially in preserving compression and contact while also resisting fatigue. Dual‐plane constructs—4‐Leg + 2‐Leg perpendicular and 5‐Hole Plate with Screw—demonstrated 2–3× higher initial rigidity than their single‐plane counterparts and showed superior fatigue resistance. Dynamic nitinol constructs demonstrated superior biomechanical durability compared to static plate‐and‐screw constructs, particularly when used in dual‐plane configurations. These findings support a shift in fixation strategy toward implants that maintain mechanical engagement under physiologic loading. In load‐bearing regions like the foot, fixation constructs must retain strength through repetitive stress. Dual‐plane dynamic nitinol implants provide continuous compression and greater fatigue resistance, making them a compelling alternative to static fixation. Future clinical studies should evaluate their impact on outcomes and hardware failure in early weightbearing protocols.