Three Dimension Finite Element Analysis And Biomechanical Study Of The Point Contact Locking Plate System

Objective:1.To investigate the distribution of stress and strain on the plate and the femur, we used the finite element analysis method to analyze biomechanic characters of the femoral shaft fracture fixed with the point contact locking plate system (PC-LP) or the limited contact dynamic compression plate system (LC-DCP) under different loading models.2. To compare biomechanic characters of the point contact locking plate system and the conventional dynamic compression plate system, we used the osteoporotic and comminuted fracture model to test the bending and torsion stiffness under different loading models.3. To compare the formation of calluses, we established the comminuted tibial fracture model of goats fixed with the point contact locking compression plate system (PC-LCP) or the limited contact dynamic compression plate system.Methods:1. The compute aided design technology and the reverse engineering technology were used to establish the three dimension models of plate and femur. After model assembles using the Pro/E software, we used the ANSA12.0 software to generate meshes. Under different loading models, we analyzed the distribution of stress and strain on the plate and the femur using the ANSYS10.0 software.2. The osteoporotic cadaveric bone was selected by the double energy X-ray machine. A 10 mm gap osteotomy model was used to simulate a comminuted fracture. Under four point bending, torsion and axial compression loading, we compared the bending stiffness, torsion stiffness and compression stiffness of the point contact locking plate system with the conventional dynamic compression plate system.3. We selected healthy mature goats and made a Z-shape osteotomy fixed with the point contact locking compression plate or the limited contact dynamic compression plate to simulate the comminuted fracture model. Through the X-ray examination, four point bending test and bone morphology study, the calluses formation of the fracture fixed with the point contact locking compression plate was compared with the limited contact dynamic compression plate.Results:1. The results of finite element analysis show that the distribution pattens of strain and stress have no significant difference between the point contact locking plate system and the limited contact dynamic compression plate. Under the axial compression and torsion loading, the stress concentration on femur screw holes of PC-LP was less than that of the LC-DCP. Under different loading models, the stress concentration on plate of the PC-LP focus on the middle of the plate or on the edge of the plate. And the stress concentration on femur screw holes of the PC-LP system focus on the middle or the distal two holes2. The osteoporotic and comminuted radial fracture was made and fixed with the PC-LCP or the DCP. Under anteroposterior four point bending, mediolateral four point bending or torsion test, the average bending stiffness or the average torsion stiffness of the radial fracture model fixed with the PC-LCP have a trend to be more than that of the radial fracture model fixed with the DCP. When the radial fracture model fixed with the PC-LP or the LC-DCP, the average bending stiffness or the average torsion stiffness of the radial fracture model fixed with the PC-LP was significant more than that of the radial fracture model fixed with the LC-DCP. When the femoral fracture model was used and fixed with the PC-LCP or the DCP, we carried out the anteroposterior four point bending, axial compression and torsion test. The average bending stiffness or the average compression stiffness of the femoral fracture model fixed with the PC-LCP was significant more than that of the femoral fracture model fixed with the DCP. And the average torsion stiffness of the PC-LCP has a trend to be more than that of the DCP.3. In the animal study, the calluses formation of the comminuted fracture fixed with the PC-LCP after the postoperative eight weeks or twelve weeks was more than that of the DCP through the radiographic results. After the postoperative twelve weeks, the average bending strenghth or the average maximum load of the tibia after removing the PC-LCP was significant more than that of the tibia after removing the DCP. After the postoperative twelve weeks, trabecular bone of PC-LCP group was more than that of the DCP group through the morphology study of calluses. Using the histomorphometry of bone, the trabecular bone volume of the PC-LCP group was significant more than that of the DCP group. But the difference of the appositional rate between the PC-LCP group and the DCP group has no significance.Conclusions:In summary, as one kind of biological internal fixation, the biomechanic property of the point contact locking plate system is significant higher than that of the conventional dynamic compression plate. At the same time, the poin contact design reduce the vascular damage around the fracture site. Thus, when we manage the osteoporotic and comminuted fracture, the point contact locking plate system is superior to the conventional dynamic compression plate and promote the calluses formation. Compared with the the conventional dynamic compression plate, the point contact locking plate system is one more ideal biological plate.