Biomechanical performance of static and NiTiNOL compression devices in first metatarsophalangeal joint arthrodesis.

Abstract

First metatarsophalangeal (MTP) joint arthrodesis is commonly performed to treat hallux rigidus. Traditional stainless steel or titanium constructs (e.g., locking plates with screws) provide sufficient stiffness but are prone to permanent deformation after excessive pre-fusion loading, leading to plantar gapping and malalignment. Superelastic NiTiNOL staples capable of sustained dynamic compression (SDC) have been developed to address these shortcomings. To compare the biomechanical performance of first MTP arthrodesis constructs using static fixation, SDC staples, or hybrid static/SDC fixation. Controlled laboratory study using synthetic MTP joint replicas. Solid foam first MTP models (N=6/group) underwent arthrodesis with one of five constructs. Specimens were cyclically loaded for 1,000 cycles at physiologic loads, followed by destructive displacement testing. Bending stiffness, plantar gapping at simulated walking loads, and permanent plantar gapping were quantified. One-way ANOVA comparisons were performed with the locking plate and screw construct as the control. Bending stiffness and plantar gapping at simulated walking loads were not significantly different across groups (p>.07). However, all SDC constructs demonstrated significantly reduced permanent plantar gapping compared with locking plate and screw (≤0.29 mm vs. 0.85 mm, p<.001). The four-leg Y staple alone or in combination with a static screw provided the highest bending stiffness and greatest reduction in permanent plantar gapping. Superelastic NiTiNOL SDC staples yield equivalent construct stiffness and markedly reduce permanent plantar gapping compared with static fixation. Hybrid constructs may further enhance biomechanical stability, supporting future clinical evaluation of SDC devices in first MTP arthrodesis.