Effects of elastic intramedullary nails composed of low Young's modulus Ti-Nb-Sn alloy on healing of tibial osteotomies in rabbits.

Intramedullary nailing is widely performed for internal fixation of fractures. The applicable elasticity of materials composing intramedullary nails remains unclear. The present study aimed to evaluate the effects of the elastic property of β-type titanium alloy nails on fracture healing compared with conventional Ti-6Al-4V alloy nails using a rabbit tibial osteotomy model. Two types of intramedullary nails composed of β-type Ti-Nb-Sn alloy (Young's modulus: 37 GPa) or Ti-6Al-4V alloy (Young's modulus: 110 GPa) were used for osteotomy fixation in the tibiae of rabbits. At 4, 8, and 16 weeks postoperatively, microcomputed tomography (micro-CT) and three-point bending tests were performed. Micro-CT images showed that the callus volume was significantly larger in the Ti-Nb-Sn alloy group at 4 and 8 weeks. The callus bone mineral density did not differ at each time point. In mechanical testing, the maximum load was significantly higher at all time points in the Ti-Nb-Sn alloy group. Taken together, the elastic intramedullary nails composed of Ti-Nb-Sn alloy improved the mechanical properties of the bone healing site from the early phase to the remodeling phase. Adequate Young's modulus of the Ti-Nb-Sn alloy enhanced fracture union and bone strength restoration. The Ti-Nb-Sn alloy is a promising biomaterial for fracture fixation devices.