Biomechanical Performance of Static Compression Devices Compared to NiTiNOL Compression Devices in Simulated First Metatarsophalangeal Joint Arthrodesis
Authors: Gonzalez Tyler , Jackson J. Benjamin , King Shannon , Gregory Kristen , Johnson James , Kline Courtney , Safranski David 
Published: December 2023

Category: Midfoot/Forefoot; Basic Sciences/Biologics Introduction/Purpose: Traditional hardware for first MTP arthrodesis procedures are typically made from stainless steel or titanium. While postoperative non-weightbearing protocols have enabled successful results with these devices, they are still prone to permanent deformation and associated plantar gapping/joint misalignment following excessive prefusion loading (e.g., patient falling). By leveraging the material properties of NiTiNOL, sustained dynamic compression (SDC) staples have been designed to recover their initial shape after large loading events. As such, implementation of these SDC staples may produce first MTP arthrodesis constructs more robust to early loading events, potentially decreasing patient immobility times and reducing incidences of postoperative joint misalignment. The goal of this study was to characterize the biomechanical performance of first MTP. Methods: Solid foam MTP replicas underwent simulated arthrodesis using one of eight constructs (N=6 replicates within each group). Groups consisted of: (1) double 2-leg staple, (2) 4-leg inline staple, (3) 4-leg Y staple, (4) 4-leg inline staple & screw, (5) 4- leg Y staple & screw, (6) double screw, (7) locking plate, and (8) locking plate & screw (Figure A-C). Simulated loading was applied to the samples 23mm distal to the joint line in the dorsiflexion direction. Samples underwent 1,000 nondestructive cycles of loading between 5-15N (replicative of postoperative walking in a recovery boot), followed by simulated overloading (destructive test) that applied 10mm of displacement at the loading point. Plantar gapping was measured using photogrammetry techniques throughout the entire testing protocol. Data were analyzed using a one-way ANOVA (α=0.05) with Dunnett’s post hoc test using the ubiquitous plate and screw group as the control. Results: Plantar gapping at simulated walking revealed significantly increased plantar gapping in the locking plate (P=.001) and double 2-leg staple (P .75, Figure D). The double screw and Y staple & screw groups exhibited significantly decreased gapping at 10mm extension as compared to the locking plate & screw group (P=.030 and .049, respectively). All SDC NiTiNOL constructs (both with and without static devices) recovered plantar gapping post-failure, with plantar gaps ≤ 0.29 mm, whereas the locking plate & screw construct group had a mean post-failure plantar gap of 0.85 mm (P <.001, Figure E). Conclusion: These data illustrate the ability of newer SDC staples to reduce plantar gapping following excessive pre-fusion loading events as compared to standard plate & screw constructs. Specifically, the four-legged Y staple & static screw construct exhibited similar plantar gapping in simulated walking and nearly eliminated permanent plantar gapping following the excessive pre-fusion loading event. While these biomechanical data do not measure clinical fusion performance, they indicate the suitability of these products in generating equivalent construct stability as compared to the currently used locking plate and screw combination, justifying future clinical studies aimed at assessing their effectiveness.