Evaluation of the mechanical properties and clinical application of nickel-titanium shape memory alloy scaphoid arc nail.

To investigate the mechanical and biomechanical properties of nickel-titanium (Ni-Ti) shape memory alloy scaphoid arc nail (NT-SAN) fixator as well as study the surgical method of treating carpal scaphoid fractures and evaluate its clinical efficacy. (1) Static and dynamic bending tests with embedded axial bending fixture were conducted to study the mechanical properties. (2) To evaluate biomechanical strength and fatigue, 32 scaphoid samples were classified into four groups to perform the fixation rigidity test: intramedullary Kirschner fixation (group A), Kirschner straddle nail fixation (group B), screw nail fixation (group C), and NT-SAN fixation (group D). Next, 24 scaphoid waist fracture models were classified to conduct fatigue experiments as follows: Kirschner straddle nail fixation (group E), screw nail fixation (group F), and NT-SAN fixation (group G). (3) The Krimmer score chart was used for clinical evaluations. (1) NT-SAN showed excellent mechanical performance and a long lifespan. (2) NT-SAN was fixated with a strong intensity and an anti-fatigue outcome. (3) Ninety-eight interviewed patients were satisfied with the therapeutic effects of the arc nail (satisfaction rate: 95.92%). The designed strength and hardness of NT-SAN corresponded with the anatomical characteristics of the scaphoid, and the designed mechanical properties met the biomechanical requirements of a scaphoid fracture. The fatigue strength can meet the requirements of bone healing after the scaphoid fracture. Clinical trials on NT-SAN scaphoid fracture treatment have shown that the surgery is simple and the clinical results are satisfactory. The therapeutic level of NT-SAN is III; thus, it is worth promoting.