The Biological Characters Of Diapyhsial Fracture Healing Of Long Bones In The Three Dimensional Memory Stress Field And The Study Of Related Mechanism Of Osteogenic Signaling

[Abstract] Objective: To explore the biological characters of diaphyses fracture healing of long bones in the three dimensional memory stress field produced by shape memory compressive connector (SMC) and to study the related mechanism of osteogenic signaling. Methods: Experimental humeral fracture model in New Zealand rabbits were used to compare the biomechanical effect of SMC on fracture healing with that of dynamic compression plate (DCP). The activity of COX-2 was inhibited by Celecoxib in some cases fixed with SMC. The temporal expression patterns of COX-1 and COX-2 mRNA at fracture gaps during the repair process were examined through real time RT-PCR. The exact content of PGE2 and cAMP at fracture gaps were detected through radioimmunity method. The mineral metabolism parameters were determined by photometric methods. The process and quality of fracture healing was observed histologically. RT-PCR was employed to study the expression levels of some extracellular matrix protein mRNA. Results: The relative levels of COX-2 mRNA as well as the contents of PGE2 and cAMP are significantly higher in cases fixed with SMC than those fixed with DCP at 3 and 4 weeks postoperatively. Accordingly, the calcium and phosphorus contents and mRNA levels for type I collagen and osteocalcin of the callus as well as the serum activity ofbone-specific alkaline phosphatase in cases fixed with SMC were significantly higher than those fixed with DCP during three to four weeks after operation. The mineralization of extracellular matrix and endochondral osteogenesis in callus also took placed earlier in the biomechanical condition of SMC. The promotion for endochondral bone formation, mineral metabolism and the expression of extracellular matrix protein mRNA in the special three dimensional memory stress field produced by SMC were impaired after COX-2 activity and the content of PGE2 and cAMP were inhibited. Conclusion: The three dimensional memory stress field contributed to the mineralization of extracellular matrix and endochondral bone formation of callus in the fracture gaps, and accelerated fracture healing. This result was considered to be closely related with the signaling pathway that had several critical components including COX-2, PGE2 and cAMP.