ABSTRACT
Objective To compare the stability of injectable pedicle screw with different lateral holes augmented with different volume of polymethylmethacrylate (PMMA) in synthetic bone block used for patients with osteoporosis,and analyze the relationship between screw stability and injected volume and distribution pattern of PMMA.Methods The synthetic bone blocks used for patients with osteoporosis were randomly divided into groups A,B,C and D according to the screw difference,and the blocks in each group were then randomly divided again into subgroups 0,1,2 and 3 according to the difference of PMMA volume.A pilot hole was prepared in advance using the same method in all samples.Pedicle screws of type A-C were directly inserted into vertebrae of groups A-C respectively,and then different volumes of PMMA (0,1.0,1.5 and 2.0ml) were injected through screw into the blocks of subgroups 0,1,2 and 3 respectively.The pilot hole was filled with different volumes of PMMA (0,1.0,1.5 and 2.0ml) followed by insertion of screw in groups D0,D1,D2 and D3 respectively.X-ray examination was performed to evaluate the screw position and PMMA distribution,and axial pull-out test was performed to measure the maximum axial pullout strength (Fmax).Results X-ray examination revealed that PMMA wrapt the anterior 1/3 part of screw in groups A1-A3,wrapt the middle 1/3 part of screw in groups B1-B3 and groups C1-C3,and evenly wrapt the full length of screw in groups D1-D3.Two factor ANOVA showed that both volume and distribution of PMMA significantly influenced Fmax (P＜0.05),but no marked interaction existed between the two factors (P=0.877).Among groups with the same screw,no significant difference of Fmax was found between the groups injected of 1.0ml and 1.5ml PMMA and those of 1.5ml and 2.0ml PMMA (P＞0.05),but the Fmax was significantly higher in groups with injection of 2.0ml PMMA than that in groups with injection of 1.0ml PMMA (P＜0.05).Among the groups injected with same volume of PMMA,no significant differences on Fmax were found among the groups A0-D0,A2-D2 and A3-D3 (P＞0.05).The Fmax was significantly lower in group A1 than in group DI (P=0.026),and no significant differences existed between the other two groups injected with the same volume of PMMA (P＞0.05).Conclusion PMMA can significantly enhance the stability of different injectable pedicle screws in synthetic bone block used for patients with osteoporosis,and the stability is significantly correlated with injected volume and distribution pattern of PMMA.
ABSTRACT
OBJECTIVE: Finite element analysis was used to compare preoperative and postoperative stress distribution of a bone healing model of femur fracture, to identify whether broken ends of fractured bone would break or not after fixation dislodgement one year after intramedullary nailing. Method s: Using fast, personalized imaging, bone healing models of femur fracture were constructed based on data from multi-slice spiral computed tomography using Mimics, Geomagic Studio, and Abaqus software packages. The intramedullary pin was removed by Boolean operations before fixation was dislodged. Loads were applied on each model to simulate a person standing on one leg. The von Mises stress distribution, maximum stress, and its location was observed. Results : According to 10 kinds of display groups based on material assignment, the nodes of maximum and minimum von Mises stress were the same before and after dislodgement, and all nodes of maximum von Mises stress were outside the fracture line. The maximum von Mises stress node was situated at the bottom quarter of the femur. The von Mises stress distribution was identical before and after surgery. Conclusion : Fast, personalized model establishment can simulate fixation dislodgement before operation, and personalized finite element analysis was performed to successfully predict whether nail dislodgement would disrupt femur fracture or not.
ABSTRACT
Objective To optimize the design of ball socket of artificial cervical joint complexity. Method A three dimension model of the artificial cervical joint complexity was constructed by the finite element method. The height range of the ball socket handle in the model was set. A simulation was manipulated to optimize the height under the physical load. The stress and strain of the joint complexity with different sizes was analyzed and the systematic safety factor was also evaluated. Results The simulation showed that the maximum Von mises stress appeared at the joint of handle and bottom in the anteflexion position. As the height of the handle increased, the maximum strain increased, and the graph of minimum safety factor was Parabola curve. Conclusions Considering the systematic stability and mobility, when the height of handle is 6 mm, the design of ball socket is considered to be optimal.
