Biomechanical Comparison Between Fixation Techniques for First-Metatarsophalangeal Joint Arthrodesis.

Background: Metatarsophalangeal (MTP) arthrodesis is the gold standard for treatment of end-stage degeneration or severe hallux valgus deformities. Traditional fixation uses stainless steel or titanium plates, often with a crossing screw. Nitinol, a superelastic nickel-titanium alloy, offers dynamic compression. Nevertheless, it is unknown how nitinol implantation in the context of first-MTP arthrodesis performs biomechanically. We hypothesized that nitinol constructs would demonstrate biomechanical performance comparable or superior to a traditional plate-and-screw construct.

Methods: Twelve pairs of cadaveric metatarsophalangeal joints were organized into 3 groups according to a balanced incomplete block design: (1) a traditional titanium plate and cross-screw (PS) construct, (2) a nitinol staple and cross screw (NSS) construct, and (3) a proprietary nitinol hybrid screw (NHS) construct. The PS construct consisted of a plate with a compression cross screw; the NSS construct consisted of a nitinol staple with a compression cross screw; and the NHS construct consisted of a hybrid nitinol staple with a compression cross screw. Each specimen was cyclically loaded over 100 cycles at 1 Hz from 20 to 90 N followed by failure testing. A high-definition camera recorded gapping. Failure load, deflection, and stiffness were recorded.

Results: Compared with the PS construct, both nitinol constructs (NSS and NHS) demonstrated significantly higher failure loads (NSS: 196 ± 101 N, P = .011; NHS: 161 ± 45 N, P = .045), greater stiffness (NSS: 33 ± 15 N/mm, P = .012; NHS: 29 ± 12 N/mm, P = .042), reduced deflection after cyclic loading (NSS: 6 ± 3 mm, P = .047; NHS: 7 ± 3 mm, P = .048), and decreased gapping at failure (NSS: 1 ± 1 mm, P = .003; NHS: 2 ± 1 mm, P = .008). No significant differences were observed between NSS and NHS.

Conclusion: Nitinol constructs for MTP arthrodesis demonstrated superior mechanical performance compared with a traditional plate-and-screw construct, with higher failure load and stiffness.

Clinical relevance: These results support the growing use of nitinol for joint fusion, highlighting its potential to improve load to failure and reduce displacement under cyclic loading.