Biomechanical Comparison Between Fixation Techniques for First-Metatarsophalangeal Joint Arthrodesis

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.

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.

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.

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

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.