ABSTRACT
Objective A novel variable-diameter cortical threaded screw used in a modified cortical bone trajectory(MCBT)was designed to verify its mechanical properties using the MCBT technique.Methods According to MCBT technology,the screw pitch was fixed at 2 mm,the total length was 45 mm,the diameter of the thick rod was 5.5 mm,the diameter of the thin rod was 4.0-4.5 mm,and the length of variable-diameter position connecting the thick rod and the thin rod was 2 mm.The parameters were set based on three aspects:variable-diameter position,thread depth,and thread type.Three-factor and three-level L9 tests were conducted and screw models were established.The torsion and the bending and pull-out force of the designed screws were calculated based on the finite element method,the results were analyzed using range analysis,and then the screw models were determined.The three-dimensional(3D)model of L4 vertebral body in osteoporosis specimens was established and screws were placed according to the MCBT technique.The pull-out force of the novel variable-diameter cortical threaded screw was compared with that of a conventional non-variable-diameter cortical threaded screw.Results Range analysis showed that screw No.6(variable-diameter position:24 mm from the screw head,thread depth:0.7 mm,45° symmetrical thread)was the optimal screw.The anti-pull-out force of the No.6 variable-diameter cortical threaded screw was 13.1%higher than that of the 4.5 mm conventional non-variable-diameter cortical threaded screw,and no statistical difference in anti-pull-out force was found between the No.6 variable-diameter cortical threaded screw and the 5.5 mm conventional non-variable-diameter cortical threaded screw.Conclusions The variable-diameter position has the smallest influence on pull-out force of the screw,the thread type has the largest influence on pull-out force,and the thread depth has the largest influence on torsion and bending.Compared with that of the conventional non-variable-diameter cortical threaded screw,the variable-diameter cortical threaded screw had a smaller front end,which prevented splitting at the entrance point of the screw.The screw has a large diameter at rear end,thereby showing improved pull-out performance.The results provide a new theoretical basis for the clinical application of MCBT technology.
ABSTRACT
BACKGROUND:At present,there are shortcomings and risks in the surgical revision of vertebral bodies that failed to be fixed in clinical practice.To avoid the risks of conventional revision surgery,the cortical bone trajectory technique is used to perform revision surgery on vertebral bodies that failed to be fixed.However,the mechanical properties of cortical bone trajectory technique screws in revision surgery are not clear. OBJECTIVE:The mechanical properties of cortical bone trajectory in lumbar revision surgery were analyzed by the finite element method to provide a theoretical basis for the clinical application of cortical bone trajectory in revision surgery. METHODS:CT scan data of the osteoporotic vertebral body were obtained and the L4 vertebral body model was established.The initial cortical bone trajectory placement and traditional pedicle screw in the L4 vertebral body model were completed,respectively,and their mechanical data were taken as the baseline standard for later evaluation of revision surgical performance.The traditional pedicle screw was removed and the screw path was retained.The cortical bone trajectory screw was used for secondary screw placement on the vertebral body to achieve lumbar refixation.The axial pull-out force,stability,and lumbar motion range of the revised screw were analyzed by the finite element method. RESULTS AND CONCLUSION:(1)The screw axial pull-out force of the cortical bone trajectory revision group was 25.6%higher than that of the traditional pedicle initial group.(2)In the lower,left,and right working conditions,the load-displacement ratio of screws in the cortical bone trajectory revision group increased by 18.5%,41.3%,and 35.0%,respectively,compared with the traditional pedicle initial group.The load-displacement ratio of screws in the cortical bone trajectory revision group was slightly higher than that in the traditional pedicle initial group under the above condition,but there was no statistically significant difference(P>0.05).(3)In anterior and posterior flexion conditions,lumbar motion range in the cortical bone trajectory revision group was increased by 45.5%and 36.1%compared with the traditional pedicle initial group,but there was no statistically significant difference in left bend,right bend,and axial rotation conditions(P>0.05).(4)There were no statistically significant differences in screw axial pull-out force,screw load-displacement ratio,and lumbar motion range between the cortical bone trajectory revision group and cortical bone trajectory initial group(P>0.05).(5)The mechanical data exhibited that although the revised nail track bone was damaged or lost to a certain extent,the mechanical properties of the cortical bone trajectory revision group were still better than those of the traditional pedicle initial group to a certain extent.Moreover,there was no significant difference in the mechanical properties between the cortical bone trajectory revision group and the cortical bone trajectory initial group.It provides a reference for revision surgery of lumbar internal fixation with cortical bone trajectory technique in patients with failed traditional pedicle fixation.
ABSTRACT
BACKGROUND:On the basis of modern design method and numerical simulation, studies can explore the action mechanisms of sand therapy in Uyghur medicine. OBJECTIVE:To explore a kind of non-homogeneous and isotropic biological bone finite element modeling method based on CT value, and to study the influence of sand therapy in Uyghur medicine on the mechanical properties of rabbits’ femur. METHODS:Eight adult New Zealand white rabbits were used to establish osteoarthritis models of right posterior femur with papain. These rabbits were divided into sand therapy group and control group. In the sand therapy group, after treatment with sand therapy in Uyghur medicine, rabbit femoral models were scanned with CT. The fault image data were imported into MIMICS software. 3D model of femur was generated. The meshing was done. The material properties were given. Three-point bending in the Ansys was simulated and solved.Simultaneously, the isolated three point bending tests were performed in al rabbit models. The corresponding deflection and the maximum stress values were obtained. Finaly, the results obtained from the three-dimensional finite element modeling method were compared with the results obtained from the experiments. RESULTS AND CONCLUSION:(1) The deflection and the maximum stress obtained by the three-point bending simulation analysis with the three-dimensional finite element model of the rabbits’ femur were wel correlated with the data obtained from the experiments. (2) These results indicate that the finite element modeling method is consistent with the structural and material properties of bone, which can be used to analyze the stress and deformation ofbones.
ABSTRACT
The present paper is aimed to study the effect of sand-therapy with Uyghur medicine on biomechanical properties and femoral bone volume of the femur of osteoarthritis (OA) rabbits at two different ages. In the experiments, we injected Papain through the joint space of right knees into the bodies of New Zealand rabbits (16 in the growing group, and 16 in the mature group), and established an OA model. The 16 rabbits in the mature group were divided randomly into 2 sub-groups: 8 in control group (no sand therapy), and 8 sand-therapy group. The 16 rabbits in the growing group were divided randomly into 2 groups as well: 8 in the control group (no sand therapy), and 8 in the sand-therapy group. We carried out CT scanning four times (1 day before, 13th, 27th and 41st days after the establishment of the model, respectively). After importing the CT data to MIMICS, the different volumes of each sclerotin were recorded and change of the percentage of each sclerotins in total femur bone volume were analyzed. Finally the rabbit femurs were given three-point bending test, the elastic load and the elastic deflection were obtained and the inertia of the section, the maximum bending stresses, the bending modulus of elasticity and the structural rigidity were calculated. The experimental results showed that (1) Compared with 1 day before and 13th day after establishment of model at maturity, the cancellous bone volume increased and cortical bone volume decreased (P < 0.05), but compared with those in the control group, the cancellous bone volume of femurs decrease and cortical bone volume increased under sand-therapy (P < 0.05). Compared with those in the control group, there were no significant changes in the deflection and cross-sectional moment of inertia in the sand-therapy group (P > 0.05), but the maximum bending normal stress, maximum load, elastic modulus, and structural stiffness (P < 0.05) in the sand therapy group were larger than those in the control group. The study showed that sand-therapy in Uyghur medicine has benign effect on bone volume of the OA rabbit femur in two ages and the mechanical properties of the OA rabbit femur at the two ages induced by sand-therapy in Uyghur medicine have been improved.