Microhardness Distribution Of The Tibia And The Local Biomechanical Environment Assessment In Tibia Shaft Fracture

Part one Micro-hardness distribution of proximal tibia in the human skeletonObjective: To measure the bone tissue microhardness in different regions of the proximal tibia,analyze the characteristics of microhardness distribution,and provide theoretical and data support for the 3D printing of bionic bone grafts.Methods: Three fresh proximal tibia were obtained and examined by X-ray and CT to exclude skeletal pathology.Each of the proximal tibia was divided into 3 sections,which were the proximal,middle and distal section.Each section was then divided into 3 parts: medial condyle,lateral condyle and intercondylar region.Bone specimens were obtained from each part.After appropriate management to the specimens,micro-indentation was performed using a micro-hardness tester in all specimens to study the hardness distribution.Results: Totally 270 indentations were made in the specimens.The average hardness of the cancellous bone was 38.46±4.76 HV.The hardness values of proximal,middle and distal segments of proximal tibia were 37.91 + 4.74 HV,36.68 + 4.53 HV,and 40.79 + 4.05 HV respectively,the difference was statistically significant.The hardness values of the medial,middle and lateral parts of the proximal tibia were 40.81±4.17 HV,36.44±4.67 HV and 38.12±4.40 HV,respectively.The difference was statistically significant.Conclusion: There were significant differences in the bone tissue microhardness in different regions of the proximal tibia.The microhardness of medial tibial condyle was greater than that of the lateral condyle and intercondylar region.The microhardness of different planes of proximal tibial bone was also quite different.The data collected in the present study would provide a data basis for the fabrication of bionic bones that are consistent with human bone elastic modulus.Part two Microhardness distribution of tibia diaphysis and the site selection of reference point indentation techniqueObjective: The purpose of this study is to explore the distribution characteristics of bone tissue microhardness in tibial diaphysis and provide theoretical support for the test site selection of the reference point indentation technique.Methods: Three fresh right tibias were obtained from 3 cadaver donors.The tibial diaphysis was evenly divided into six sections.Bone specimens with a thickness of 3 mm were cut from each part.After appropriate management,micro-indentation tests were performed in various regions of the specimens to acquire the microhardness values of the tibial diaphysis.Statistical analysis was performed by randomized block design variance analysis to study the distribution characteristics of bone microhardness.Results: 72 regions were selected for 360 effective indentations.Different from previous researches,we found that the bone microhardness is inhomogeneous in tibia diaphysis.Mean hardness value of the anterior,medial,posterior,lateral region of tibia diaphysis is 45.58±4.39 HV,52.33±3.93 HV,54.00±4.21 HV,52.89±4.44 HV,respectively.The anterior cortex exhibits lower microhardness value than the other regions(P<0.001).Within the same region,microhardness varies significantly with positions in the tibial diaphysis.The variations in indentation hardness are bound to have a significant impact on the comparability of different RPI studies.Conclusion: Based on the results of this study,we proposed two recommendations for test site selection of RPI technique.First,the test sites of the RPI technique be selected in the same region of the tibia,in close proximity to obtain precise results.Second,the indentation hardness variation among individuals should be considered in the experiment design of RPI technique.Microhardness is a good predictor of Young's modulus of bone tissue,results of the present study would benefit the 3D printing of the bionic bone and gradient elastic modulus implants.Part three Plating system design determines the mechanical environment in tibial shaft fracturesObjective: Internal fixation devices failure is rare but unavoidable.Fatigue-related mechanisms are responsible for the most part of the mechanical failures of orthopedic plates.Plate design needs to be optimized for both long fatigue life and bone healing,only in this way can we reduce the occurrence of internal fixation failure.To address this issue,we aimed to provide a theoretical basis for improving the design of orthopedic plates.Methods: Finite element method was employed to conduct a computational investigation.3 groups of plate models were designed with varied working lengths and other elements.By fixing these plates to tibia mid-shaft fracture models,parameters of the mechanical environment around the fracture site were recorded and analyzed.Results: Plate working length,the existence of holes in working length and plate length are important factors influencing the mechanical environment of the fracture site.Screw-bone interface is the weakest part in internal fixation failure.Fractures fixed by traditional plates which had holes in working length have larger interfragmentary movement,and the plates experienced more severe stress concentration than plates without holes in working length.Conclusions: We proposed some suggestions for the plating system.First,partial weight bearing is recommended in the early postoperative period.Second,the working length of plates does have an optimal range,depending on the types of fracture.Finally,the hole within the working length should be removed to avoid stress concentration and facilitate fracture healing.Based on findings from this study,recommendations can be developed to improve clinical practices and plating system design.Conclusions:1.There were significant differences in the bone tissue microhardness in different regions of the proximal tibia.The microhardness of medial tibial condyle was greater than that of the lateral condyle and intercondylar region.The microhardness of different planes of proximal tibial bone was also quite different.2.There were significant differences in the bone tissue microhardness in different regions of tibial diaphysis.The anterior cortex exhibits lower microhardness value than the other regions.The test sites of the RPI technique be selected in close proximity to obtain precise results.3.The design of the plating system has a great influence on the mechanical environment around the fracture site in tibia shaft fracture.Plate working length,the existence of holes in working length and plate length are important factors influencing the mechanical environment.The results of this study help to optimize the design of the plating system,which can promote fracture healing and reduce the possibility of fatigue failure of internal fixation.