Serum N-terminal Telopeptide of Type I Collagen Concentration for Early Diagnosis of Fracture Nonunion in Rabbits

Abstract：Objective Purpose The aim of this study was to establish an experimental animal model of fracture nonunion, and investigate the changes in serum biomarker concentrations in fracture nonunion. Methods Twenty purebred New Zealand rabbits were divided into two groups. In the bone defect group,a 15-mm length of bone( including the periosteum)was re-moved from the mid-radius,and the medullary cavities were closed with bone wax. In the bone fracture group,the mid-radius was fractured. X-rays were taken and blood samples were collected preoperatively and at 2,3,4,5,6,7,8,10,and 12 weeks after surgery. The serum concentrations of bone-specific alkaline phosphatase( BSAP)as markers of bone formation,and of N-terminal telopeptide of type I collagen(NTX),and tartrate-resistant acid phosphatase 5b(TRACP 5b)as markers of bone resorption,were measured using biotin double -antibody sandwich enzyme -linked immunosorbent assay. Results In the bone defect group,bone callus was observed on X-ray at 2 weeks in three rabbits and the bone calluses stabilized at 5 weeks, but none of the bones had healed at 8 weeks. In the bone fracture group,the fracture line was blurry at 2 weeks and bone callu-ses formed at 6-8 weeks. In the bone defect group,the serum BSAP and TRACP 5b concentrations increased after surgery, peaked at 4 weeks,began to decrease at 5 weeks,and stabilized after 6 weeks. The serum NTX concentration fluctuated during the first 4 weeks,was significantly lower at 5 weeks than at all other time points,and stabilized after 6 weeks. Conclusion These results show that a bone nonunion model can be established in New Zealand rabbits by resecting a 15-mm length of bone from the mid-radius with bone wax blocking. Measurement of the serum BSAP,NTX,and TRACP 5b concentrations may be useful for the early detection of bone nonunion. The serum NTX concentration changed significantly in rabbits with bone nonunion. Further studies are needed to determine the feasibility of using the serum NTX concentration for the early diagnosis of bone nonunion.