| Background:It is well known that the process of fracture healing is mainly due to a series of cytokines,such as VEGF,TGF-?1 and BMP-2,etc.,this cytokines involved in the vascular regeneration,callus formation and callus remodeling.Stress-stimulating can also promote the healing rate of fractures,but the relationship between cytokines and stress is unclear.In the early stages of this study,we developed a patented percussion bone stress stimulator,to simulate the human tibia and heel parts of the load-bearing situation,the initial verification of axial stress to promote fracture healing.However,the molecular mechanism of in vitro axial stress stimulation on fracture healing and the cytokines that affect these molecular mechanisms have not been very clearly.With the progress of science and technology,especially the development of molecular biology technology,we have found a lot of method to explore the molecular mechanism of post-fracture healing process,provide technical support for understand the law of fracture healing and various factors on the impact of post-fracture healing process.Aim:In the early stages of this study,the initial optimized axial stress parameters of the rabbits in this experimental animal were simulated by computer simulation.The parameters were 15N and 1Hz.accordingly,we established the rabbit tibial fracture model and divided into experimental group(with the axial stress)and control group(without plaster fixation only).The sample will be get at the proposed time.The effects of axial stress on fracture healing were discussed from the imageology,biomechanics and molecular biology.Found out the role of cytokines in this process,all of this will provide a reliable axial Stress to promote the molecular basis of fracture healing,for the follow-up experimental study to lay a solid theoretical basis.Methods:The tibial fractures were established with 120 rabbits.After the operation,those rabbits were divided into 8 groups randomly.In the experimental group,the stress stimulus was started on the 8th day after operation.The stress was stimulated every 2days,30 minutes each time,the stress parameter was 15N,the frequency was 1Hz,the percussion time was 5s,and the intermittent time was 3s.The control group was treated with plaster fixation only.According to the experimental plan,the rabbits were photographed by X ray at the 2nd week,the 4th week,the 6th week and the 8th week after the modeling.Then the rabbits were sacrificed,obtain bone samples for general observation and molecular mechanism studies.Biomechanical experiments were performed at the 8th week.Results:The results of X-ray showed that the neonatal callus and callus remodeling in the experimental group were better than the control group.In the experimental group(6th week),the healing level was reached in the control group(8th week).The Lane-Sandhu score of bone healing showed that the Lane-Sandhu scores of the experimental group at 4th,6th and 8th weeks were significantly higher than same time in the control group(P<0.05).Three-point bending and torsion test results showed that the difference between the experimental group and the control group was statistically significant at the 8th week after the fracture(P<0.05).The results of HE staining showed that the number of cells in the experimental group was higher than that in the control group at the 2nd week and the 4th week,the experimental group was more mature;at the 6th week,the hard callus appeared in the outer layer,the callus and the fibrous tissue were found in the medullary cavity,the callus in the experimental group was larger than that in the control group;at the 8th week,the outer callus was more abundant in the experimental group,and the callus and fibrous tissue were seen in the medullary cavity,while the control group was less.Immunohistochemical results showed that,both the 2 groups the expression of CD34+ reached the peak in the 4th week,the experimental group in the 2th week and 4th week is more than the control group,the difference was statistically significant(P<0.05),and the expression of the 2 groups were down in the 6th week and 8 weeks,no significant difference.VEGF was highly expressed in the whole process,both the 2 groups reached the peak in the 4th week,and the expression of the experimental group always more than the control group in the whole process,the difference was statistically significant(P<0.05).The expression of the TGF-?1 reached the peak at the 4th week both the two groups,there was significant difference in the 2 week and the 4th week(P<0.05).There was no significant difference in the 6th week and the 8th week.BMP-2 can be detected at the 2th week,the expression level reached the peak in the 6th week,we found that the experimental group compared with the control group,in the phase and expression were significantly improved,with statistical significance(P<0.05).In the follow-up Western Blot test,we examined the VEGF protein of the sample,the results showed that the experimental group was higher than the control group in each time period,and the expression level was the highest at the 4th week,The results were more consistent,the difference was statistically significant(P<0.05).Conclusions:The vitro axial stress can promote the healing of rabbit tibial fractures.We found that the molecular mechanism of its role is mainly through the recruitment of CD34+cells in the hematoma machine,induced by TGF-?1 synergistic VEGF formation of new blood vessels and the original callus,and VEGF also plays an important role in the follow-up callus remains,BMP-2 play a key role in callus formation and bone tissue formation process.The vitro axial percussion stress stimulation can enhance the expression of those cytokines,and thus faster to promote fracture healing,and the newborn bones are stronger.This study provides a theoretical basis for the study of subsequent stress stimulation to promote fracture healing. |
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