Experimental Study Of Impact On Fracture Healing By PDLLA Absorbable Intramedullary Rod

[Objectives] To compare and evaluate the differences of curative effects and biological mechanisms underlying the posttraumatic bone healing between traditional metal products and PDLLA absorbable materials for the intramedullary internal fixation of fracture.[Methods] To establish an open osteotomy model of SD rats using internal fixation of traditional metal products(Kirschner) and PDLLA absorbable intramedullary rod. Using X-ray,microCT,Biomechanical index to dynamically evaluate and compare the curative efficacy about the posttraumatic bone healing. Using the method of ABC-ELISA(avidin biotin peroxidase complex enzyme-1inked immunosorbent assay), the serum concentrations of sRANKL(soluble receptor activateor of nuclear factors-κB ligand), OPG(osteoprotegerin), TRACP-5b(Tartrate resistant acid phosphatase 5b), and the ratio of OPG/sRANKL were assessed. Using the method of immunohistochemistry, the tissue localization of RANKL,OPG, and Wnt were detected. Using the method of Western Blotting and real-time RT-PCR, the protein and mRNA expression levels of RANKL, OPG, Wnt, β-catenin, and Runx2(core binding factor alpha1 subunit protein/runt related transcription factor 2) in callus tissue were determined.[Results] At 4, 6, and 8 weeks after surgery, compared to that of metal intramedullary fixation products, the growth of trabecula in callus was significantly promoted after using the PDLLA absorbable material for intramedullary fixation(p<0.05). There were no significant differences in biomechanical experiment results(p>0.05). At 4 and 6 weeks after surgery, compared to that of metal intramedullary fixation products, the serum concentrations of sRANKL, OPG, and the ratio of OPG/sRANKL were significantly increased after using the PDLLA absorbable material for intramedullary fixation(p<0.05). At 4 and 6 weeks after surgery, compared to that of metal intramedullary fixation products, the protein and mRNA expression levels of RANKL, OPG, Wnt, β-catenin, and Runx2 in callus tissue were significantly elevated(p<0.05).[Conclusion] Compared to that of metal products, the curative efficacy of the intramedullary fixation for fracture could be significantly promoted after using the PDLLA absorbable material, and the improvement of curative effects were associated with the changes of Wnt/β-catenin 、 Runx2 signaling and RANKL/OPG mediated biological processes.