Biomechanical Research Of Locking Plate In Treatment Of Femoral Shaft Fractures

For the treatment of femoral shaft fractures, there are usually three choices of implants: intramedullary nailing, locked plate and compression plate. There are both advantages and disadvantages of different fixation methods: Although intramedullary nailing is the central axis fixed, serious destroy the blood supply to the bone marrow. Locked plate fixation is convenient and easy, but requires a lot of periosteal stripping, and easily deviate from the fixed central axis. Compression plate has great intensity, but there is stress shielding effect. Because medical stainless steel and titanium have good biocompatibility to the human body, they are the most commonly used clinical fracture fixation material. Clinical experience has shown that too many screws easily caused plate failure because of the stress concentration. However, fewer screws are used, the system will lead to inadequate fixed stability. The purpose of this study is to use of titanium locking compression plate, for femoral shaft fracture transverse shape, using a numerical method to determine the optimal number and the best position of screws to ensure the strongest stability of the femur bone plate system. To avoid the failure of internal fixation as much as possible, and strive to achieve the best therapeutic effect.In this thesis, by using a numerical simulation approach, the computer tomography(CT) data to be imported into Mimics15.0 software in the DICOM format, using reverse engineering techniques to extract the three-dimensional of the femur model and creating a middle transected 2 mm femoral fractures. Built a three-dimensional model of 14 holes-locked plate and selected the appropriate screws by using of computer-aided design(CAD) and UG software. According to the principle of plate mounted on the tension side of the femur, different number and different position of screws in locking plate fixation system models were assembled in the UG8.0.The backbone of the middle of shares simulated clinical trials transverse fracture. Three-dimensional model of locking plate fixation system is set the boundary conditions, imposed fixed load, given the material parameters, set contacts and connections, then meshed for each different situation, solved the stress distribution of bone plates, calculated the femur- locking plate system overall deformation under the same axial compressive force and torque load femur- locking plate system in the ANSYS WORKBENCH 15.0. Came out the impact of the total displacement stress and strain distribution on femur- locking plate system of different screw position and the different number of screws.Numerical simulation results indicated that the number of femoral screws has a significant influence on the fixed lock plate system stability: With the increasing of the screw, the stability of the system is enhanced, inserted all the screws offered maximum fixed stability. However, the number of screws implanted too much can lead to bone plate, which the stress concentration at the plate screw holes in the middle of seventh and eighth, easily lead to failure at high frequent plate axial load.screw locations on the femur- locking plate system has a significant impact on the stability of a fixed numerical simulation. Results showed that the shorter the distance plate across the fracture, the higher corresponding strain was. Locking plate was easy to concentrate stress due to the stress caused by fatigue failure, but short of the working length ensured the higher stability of the system. With the increasing in the length of the plate across the fracture zone, the stability of the system was reduced. However, due to the longer distance dispersed deformation, deformation of the plant decreases, the possibility of fatigue failure of the implant was reduced. Therefore, the stability of the working long lines system was better than shorter working line in the same circumstances.Screw position affected the stability of the locking compression plate internal fixation system. When the fracture was not installed 7,8 screws, the closer fixed screw position to the fracture, the better the stability of the system. But when the fracture 7,8 screws installed, the both ends of the plate mounting screws have a significant impact on the stability of the system, in addition,other positions of the screw changed not affected fixation stability of the system much more. Simulation results show that the shorter the distance plate across the fracture, the higher the corresponding strain,the more stress is concentrated, which easily lead to fatigue fracture of a bone plate. But it can ensure the higher stability of the system. Accordingly, the stability of the working longer line is better than that of shorter line under the same circumstances.The number of screws affected the stress and strain of the locking compression plate fixation system. In the 6 groups model, maximum stress and maximum strain of the system concentrated one threaded hole which near the greater trochanter. With the increasing in the number of screws, the maximum stress reduced, however, when the number of installation screws more than 8, this downward trend is not obvious.Screw position affected the stress and strain of the locking compression plate fixation system. When the number of screws is the same, longer working line is better than a shorter working lines. When 7,8 screws were installed, the maximum stress occurs at the 7th screw hole, the stress mainly distributed in the bone plate between 7-8 screws.The closer screw position to the femoral fracture section, the shorter the working length is, the more obvious stress concentration has.