| [Objective]To analyze Finite element of biomechanical property of four different Fixation techniques of sacral screw, to provide powerful basis of theory and practice for selecting the best fixation techniques of sacral screw and directing clinical restoration and reconstruction the stability of spine . [Methods]1. Six cases of adult cadaver specimens which was soaked and fixed in 10% formalin liquid had been used in this study, select four Fixation techniques of sacral screw included of PTSF method , anteromedial sacropromontory method (the techniques were inserting sacral screw anteromedially with a cephalic30° to 35°)and anteromedial sacral screws method (the fixation techniques were inserting the sacral screw anteromedially to pass through unicortical and bicortical anterior cortex ). Two methed of four Fixation techniques of sacral screw were randomly assigned to each side (left versus right) of sacrum with sacral screws of CD2(sofamor-Danck) (6.5×45mm). in order to better understand their biomechanical behavoirs and the maximam insertion torque of each screw .2. With an cyclic loading using biomechanical instrument (MTX858 Bionix) from 40N to 400N was applied to each screw at a frequency of 2Hz up to 20000 cyclic .stiffness was monitored during cyclic loading .and pullout tests were conducted after the completion of the fatigue tests.3. Based on the helix computed tomographic (CT) pictures, the three-dimensional geometrical model of sacrum was derived through automated computer aid design (auto CAD) technology, the mechanic parameters obtained from the literature were applied to the model,and the three- dimensional finite element model of intact sacrum was constructed, The indexes and trabecular distributive were compared. Real material properties of trabecular tissue were found. Inserting simulations of sacral screw were conducted to observe mechanic distribution in different modes The influences of indexes on material properties were also investigated.[Results]1.In the middle of four Fixation techniques of sacral screw, PTSF method, anteromedial sacropromontory method and anteromedial unicortical and bicortical sacral screws method . the maximam torque and average anti-pull-out force following cyclic loading were the significantly highest in the fixation of PTSF method . Which was mean 3.32Nm and 1623N respectively. Than that in the fixation anteromedial sacropromontory method and anteromedial unicortical and bicortical sacral screws method . Which was mean 3.16Nm , 1.97Nm , 1.28Nm and 1451N, 1131N, 785N respectively.2. During the process of cyclic loading .stiffness dropped rapidly over the first 5000 cycles. And then leveled off to an almost constant stiffness with increasing cycle in four metheds . the final stiffness of fixation of PTSF method was higher than the other three metheds. four Fixation techniques of sacral screw had shown high correlations between insertion torque and pullout strength following cyclic loading .and the correlations coefficant were 0.95 ,0.94, 0.96and0.95 respectively. 3. The results showed that anti-pullout force were caused by more trabeculae and higher density of bone. Ratio of anti-pull-out would be higher as long as material properties, such as stiffness, shear modulus and Young's modulus of trabecular tissue, were stronger. [Conclusions]To compare the four Fixation techniques of sacral screw, PTSF method,anteromedial sacropromontory method and anteromedial unicortical and bicortical sacral screws method .the superiority of mechanics were decreasing .PTSF fixation techniques of sacral screw is the most rigid way of sacral fixation, anteromedial sacropromontory method is the second, and anteromedial unicortical sacral screws method is the worst .this promising technique should be adopted in clinical practice appropriately. |
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