Structure Design And Mechanical Performance Evaluation Of Personalized Tibial Fracture Internal Fixation System

With the continuous improvement of fracture internal fixation concept,various internal fixing systems have been widely used in fracture treatment,of which the most commonly used internal fixing system is the bone plate.Due to individual differences in skeletal morphology and fracture type,insufficient matching of the consistency of plate to the skeletal surface and screw location is common.In addition,the high rigidity of traditional plate structure will result in stress shielding,which will cause delayed union of fracture and osteoporosis,causing additional pain to the patients.Metal 3D printing technology combined with personalized design of bone plate can produce bone plate with good individual matching and low stress shielding rate,which has a great application prospect in fracture internal fixation.At present,the researches mainly focus on the structural design and finite element analysis of the personalized bone plate.In fact,the mechanical properties of the personalized bone plate and its system are important factors to ensure effective fracture healing,but the research on this aspect has not been reported yet.In addition,although the design system and materials research of fracture internal fixation system have been developed maturely,the real threedimensional mechanical fixation has not been achieved in clinical practice,and the operation is difficult.Therefore,it is of great significance to study the mechanical properties of personalized plate and fixing system for fracture healing and to find a new internal fixing method to meet the requirements of three-dimensional mechanical fixing in fracture area for achieving better therapeutic effect of fracture.In this thesis,the technical route of combining finite element numerical simulation with in vitro mechanical test is used to compare and study the mechanical properties of personalized unslotted plate,personalized slotted plate,nail-rod internal fixing system,traditional straight plate for fixing 42-A simple fracture fixing system of lower 1/3 section of tibial,and three different nail-rod internal fixing systems for fixing multi-segment comminuted fracture.The design scheme of nail-rod internal fixing system which meets low stress shielding rate and stable fixing is put forward.The mechanical properties of the new internal nail-rod fixation system which meets the requirements of three-dimensional mechanical fixing were designed and evaluated by welding method.The main conclusions are as follows:(1)Four-point bending dynamic and static mechanical tests show that the static and dynamic fatigue properties of 3D-printed individual TC4 titanium alloy plate are lower than those of traditional straight-type plate due to internal hole defects.In vitro service test of the plate-tibial system fixed behind the bovine tibial bones shows that there is no crack failure failure failure of the personalized plate and the traditional straight plate under different axial compression loads,and they can withstand compression fatigue test and achieve effective fixation.The difference is that the torsion resistance of personalized bone plate is better than that of traditional straight bone plate.The stress shielding rate of the personalized plate is much lower than that of the traditional straight plate,and the stress shielding rate of the slotted design is the smallest.The experimental results indicate that the personalized 3D printing TC4 titanium alloy plate system has the potential to replace the traditional straight plate.(2)Finite element mechanical simulation of the screw-rod internal fixing system for 42-A type simple fracture in the lower 1/3 section of tibia shows that the screw-rod internal fixing system has a smaller stress shielding rate than the traditional straight bone plate by adjusting the angle between the diameter of the titanium rod and the screw.The finite element mechanical simulation results of the screw-rod internal fixing system for multi-segment comminuted fractures show that the multiple bones can be joined together stably by adjusting the diameter of the titanium rod,the number of screws and the spatial layout,which not only achieves stable internal fixing,but also has a lower stress shielding rate.The research results provide a new idea for the design of the nail-rod internal fixing system.(3)A new type of resistance spot welding connection is used to connect the nail-rod system.The mechanical properties of the resistance spot welded joint of the nail-rod internal fixation system increase with the rise of welding current and titanium rod diameter.After 3.4kA welding current was used to weld and connect the nail-rod internal fixation system for 42-A simple fracture of the lower 1/3 segment of tibia,its torsional resistance was enhanced and achieved three-dimensional mechanical fixation.In the axial compression test and fatigue test under different loads,the effect of welding fixation is equivalent to that of traditional straight plate.The finite element simulation and experimental results of multi-segment comminuted fracture show that the more the number of screws and the larger the diameter of titanium rod of the three kinds of nail-rod internal fixation systems,the better the stability of the internal fixation system can be.