Objective       To study the effect of novel dynamic compressive interlocking intramedullary nail on histology of fracture healing and expression of type Ⅰ collagen and osteocalcin in callus.       Methods        Fifteen 2-years-old goats were included in this study. A bilateral middle femoral shaft transverse fracture model was established. Its experimental side was internally fixed with dynamic compressive intramedullary nails to produce continuous dynamic compressive stress and its opposite side was fixed with ordinary intramedullary nails. Samples were taken from the healed fracture on days 7

14

30

60 and 90

respectively

after operation. The fracture healing was assessed by histopathology and RT-PCR

respectively.       Results        Histology examination showed that the calcification of cartilage matrix in the fracture space and the reconstruction of osteogenesis and woven bone within the cartilage were faster in the experimental side than in the opposite side. RT-PCR displayed that the expression levels of type Ⅰ collagen and osteocalcin were higher after operation than before operation

reached their peak on days 14 and 30 after operation respectively

and were significantly higher in experimental group than in control group (P0.05).       Conclusion        Novel dynamic compression intramedullary nail can effectively accelerate the healing of fractures by stimulating the bone extracellular matrix synthesis

secretion and formation of endochondrostosis.