Objective      To evaluate the effect of a new nano-hydroxyapatite/polyamide 66/glass fiber (n-HA/PA66/GF) bioactive bone screw on fixing femur intercondylar fracture in dogs.       Methods      The n-HA/PA66/GF bioactive bone screws were prepared. Twenty-four dogs were randomly divided into a bioactive bone screw experimental group and a metal screw control group. The dog models of femur intercondylar fracture were established using an electric saw

and the fractures were fixed with bioactive bone screws and metal bone screws

respectively. Gross examination

histological staining

CT examination

biomechanical test

blood routine and biochemical examination were performed at 4

8

12 and 24 weeks after operation. Histological staining of liver

kidney and spleen was performed at 24 weeks after operation.       Results      Both the two types of bone screws could fix the fracture effectively. The activity of the dogs was normal and the cut healed well in both of the two groups after operation. CT examination showed the femur intercondylar fracture got osteal healing at 12 weeks after operation in all the dogs. Histological investigation showed the n-HA/PA66/GF bone screws formed tight bonding with the surrounding new bony tissues

which calcified gradually into mature bony tissues. However

there was a big space between the metal bone screw and bony tissues

and a layer of fibrous tissue proliferation and encapsulation occurred on the interface between the bone and metal bone screw. The biomechanical test demonstrated the maximum push-out load showed no statistically significant difference (P0.05) between the two groups at 4

8 and 12 weeks after operation

but the difference was statistically significant (P0.05) at 24 weeks after operation. The maximum push-out load of the bioactive bone screws was greater than that of the metal bone screws. The blood routine and serum biochemical indices were normal except for the increased level of alkaline phosphatase (58.8±14.49 U/L) at 24 weeks after operation. The histological staining of liver

kidney and spleen was normal at 24 weeks after operation.       Conclusion      The n-HA/PA66/GF bioactive bone screw has good internal fixation capacity and biocompatibility

and is a promising orthopedic biomaterial.