Study On The Changes Of Microscopic Physicochemical Properties Of Femoral Neck Cortical Bone And Its Effect On Bone Strength During The Development Of OP

With the improvement of living standards and the improvement of medical conditions,the average life expectancy of human beings has been extended,and osteoporosis has become one of the three major killers that endanger the health of middle-aged and elderly people in our country alongside diabetes and cardiovascular disease.Osteoporosis(OP)is a systemic metabolic bone disease characterized by decreased bone mass and degeneration of the microstructure of bone tissue,resulting in increased bone fragility and susceptibility to fractures.Osteoporotic fracture is a serious complication of osteoporosis.It is one of the main causes of disability and death in elderly patients.Hip fracture is is one of the most serious osteoporotic fracture.It has become a serious threat to global public health problem.Therefore,optimizing the diagnosis method of osteoporosis and perfecting the risk assessment system of osteoporotic fractures have become problems to be solved urgently.However,in clinical work,the bone mineral density(BMD)measured by dual energy X-ray absorptiometry(DXA)has become an urgent problem.BMD is the main reference index for the diagnosis of osteoporosis,fracture risk prediction and curative effect evaluation.However,the results of the diagnosis of osteoporosis based on the bone mineral density measured by DXA are often inconsistent with the actual clinical situation: the bone mineral density of some fragility fracture patients does not meet the WHO diagnostic criteria for osteoporosis.Previous studies have found that,in the progress of osteoporosis,the structure of bone tissue gradually degenerates,and the microchemical composition and micromechanical properties are also developing in a direction that is not conducive to the mechanical strength of bone tissue.Existing evidence suggests that,in addition to bone mineral density,changes in the microscopic level of bone can also reflect the severity of osteoporosis.At present,the changes in the microstructure,microchemical composition,and micromechanical properties of cancellous bone in the progress of osteoporosis and their relationship with bone strength have been basically understood.Compared with cancellous bone,cortical bone plays a more important role in the overall mechanical strength of the femoral neck.However,during the occurrence of OP and OP fractures,how do the microstructure,micromechanical properties,and microchemical composition of cortical bone change,the interaction between the three,and the role of the three in the bone macromechanical strength,there is still little research at present.Therefore,in-depth study of the changes in the microscopic level of the femoral neck cortical bone during the process of osteoporosis and its relationship with the macromechanical strength of bone tissue is very important for the prevention and treatment of osteoporosis and the risk assessment of osteoporotic fractures.Purpose: Starting from the three aspects of cortical bone: microstructure,micromechanical properties,and microchemical composition,using micro computed tomography(Micro-CT),nanoindentation experiment,compression experiment,Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)to detect the changes of cortical bone microstructure,micromechanical properties,microchemical composition and macromechanical strength of cortical bone during the OP process,and analyze the interaction between the three and the role and weight of the three factors in the macromechanical strength of cortical bone,and establish the dose-effect relationship between the three micro-aspects of cortical bone and the dose-effect relationship between the three and the macro-mechanical properties of bone.Methods: A total of 115 patients who were hospitalized in the Western Theater General Hospital from January 2017 to December 2019 and met the enrollment criteria were selected to measure their femoral neck bone mineral density,referring to the World Health Organization(WHO)recommended diagnostic criteria for osteoporosis and combined with the "Guidelines for the Diagnosis and Treatment of Primary Osteoporosis(2017)",the BMD was quantified by the T value,and subjects were divided into normal groups(T≥-1.0 SD),osteopenia group(-2.5 SD<T<-1.0 SD),OP group(T≤-2.5 SD or femoral neck fragility fracture),severe OP group(T≤-3.5 SD or T≤-2.5 SD + fragility fracture).Micro-CT is used to measure the relevant parameters of the microstructure of the femoral neck cortical bone.The nanoindentation is used to measure the relevant parameters of the micromechanical properties of the femoral neck cortical bone.The relevant parameters of the microchemical composition of the femoral neck cortical bone are analyzed by FTIR and XRD.Use the axial compression test to measure the macromechanical strength of the femoral neck.Pearson correlation analysis was performed on the result data of the above experimental items,and multiple linear regression was used to analyze the weight of the influence of the femoral neck cortical bone microstructure,micromechanical properties,and microchemical composition on the femoral neck macromechanical strength.Results:(1)Micro-CT examination showed that,from normal to severe OP,the bone mineral density of the femoral neck cortical bone gradually decreased,and the total porosity gradually increased.The differences between the groups were statistically significant(P<0.05).Except for the significant difference in the thickness of cortical bone between the normal group and the OP group,the normal group and the severe OP group,the difference between the other groups was not statistically significant(P>0.05).(2)The axial compression test showed that,the maximum load of the femoral neck showed a significant decrease,and the differences between the groups were statistically significant(P<0.05).(3)The nanoindentation experiment showed that,from normal to severe OP,the elastic modulus of femoral neck cortical bone gradually decreased,and the differences between the groups were statistically significant(P<0.05).Except that there was no significant difference in hardness between the normal group and the osteopenic group(P>0.05),the differences between the other groups were statistically significant(P<0.05).(4)FTIR analysis showed that the femoral neck cortical bone mineral matrix ratio of the severe OP group was significantly lower than that of the normal group and the osteopenic group(P<0.05),and the cortical bone mineral matrix ratio of the OP group was significantly lower than the normal group(P<0.05),the differences among the other groups were not statistically significant(P>0.05).From normal to severe OP,the cross-linking ratio and mineral crystallinity of femoral neck cortical bone gradually increased,and the differences between the groups were statistically significant(P<0.05).(5)XRD analysis showed that from normal to severe OP,the crystal size gradually increased,and the differences between the groups were statistically significant(P<0.05).(6)Pearson correlation analysis shows that there are significant correlations among the relevant parameters of the cortical bone microstructure,micromechanical properties,and microchemical composition.(7)The relevant parameters of cortical bone microstructure,micromechanical properties,microchemical composition and the maximum load are all significantly correlated.(8)Among the two indicators of micromechanical properties,the elastic modulus has the strongest correlation with the maximum load.Among the three indicators of microstructure,the correlation between cortical bone mineral density and maximum load is the strongest.Among the four indicators of microchemical composition,the grain size has the strongest correlation with the maximum load.(9)Multiple linear regression analysis shows that,among all the microscopic parameters,the correlation between the elastic modulus of the femoral neck cortical bone and the maximum load of the femoral neck is the strongest.Conclusions:(1)From normal to severe osteoporosis,various microscopic parameters of cortical bone gradually change and all can affect the femoral neck macroscopic mechanical strength.(2)Among the related indexes of cortical bone’s micromechanical properties,microstructure,and microchemical composition,the indexes that have the strongest correlation with the femoral neck macroscopic mechanical strength are elastic modulus,mineral density,and grain size.(3)Among all the microscopic parameters,the elastic modulus of the femoral neck cortical bone has the greatest influence on the femoral neck macroscopic mechanical strength.(4)The evaluation of these microscopic parameters can clarify the mechanism of the microscopic physical and chemical properties of the femoral neck cortical bone on the macromechanics of the femoral neck,and provide a theoretical basis for the prevention of osteoporosis and osteoporotic fractures.