| Objective:To measure the image anatomic parameters of different insertion points of S1 cortical bone screws by CT,and to provide a reliable morphology theoretical basis of new cortical bone trajectory screw in S1.The biomechanical characteristics of L5/S1 segment fixation were simulated by using the finite element analysis method with new S1 cortical bone screws,traditional S1 cortical bone screws and S1 pedicle screws.It can provide a more reliable theoretical basis for the clinical practice of treating lumbosacral degenerative diseases,preventing sacral 1 screw loosening and pseudarthrosis,and exploring more stable and safe internal fixation techniques.Methods:1.30 healthy adults,including 13 males and 17 females,aged 40-70 years(52.3±9.99),were randomly selected to receive lumbar spiral CT scan in the East Hospital of Shan dong Provincial Hospital from August 2016 to August 2017.All the scan data was passed into the GE-AW4.3 post-processing system,The new S1 point was 3mm below the midpoint of the superior articular facet,with the direction from inside up to outside down.The nailing point with cortical bones passed through the superior articular facet,the external upper edge of the pedicle,and the anterior wall of the vertebral body.According to relationship between the bone mineral density and bone strength by the average CT value,The CT value in region of interest(ROI)and the diameter,length,cranial and caudal angle of screws around the screw track were measured by three-dimensional reconstruction to simulate and compare new S1 cortical bone screws,traditional S1 cortical bone screws and S1 pedicle screws.2.The clinical data of a 40 years old healthy man was scanned by GE spiral CT,and 256 CT images of L3-S1 segment were obtained and saved in DICOM format,and then transferred into the mimics.The target areas on each layer of images were marked,and filtered with gray threshold by Mimics software,and then the images were fused to obtain an accurate STL grid model.Each DICOM format image depicts the clear bone boundary and intervertebral disc contour after adjusting the appropriate gray level.We exported the model to STL format,and then transfered it into Geomagic software for reconstruction,repair,deburring,paving and other operations.Finally,the model surface was encapsulated to generate IGES format 3D graphics file.The bone contour was successfully established,and then the intervertebral disc and facet joints were constructed by SolidWorks software,and transferred to the ANSYS Workbench 18 software.The normal model in L5/S1.model A with traditional S1 pedicle screws.model B with traditional S1 cortex bone screw and model C with the new S1 cortex bone screw were established.The biomechanical analysis of three models was executed to compare the range of motion,stress on S1 screw,vertebral displacement,stress on vertebral,stress on the fusion cage device,stress on the internal fixation device by simulating flexion,extension,left bending,right bending,left torsion and right torsion.Results:1.There were no significant differences in the diameter of the left and right,the inclination angle of the cranial and caudal among the three kinds of screws(P>0.05).The left and right length of new S1 cortical screw(38.38±2.91 and 39.93±3.3 8mm)was longer than the traditional S1 cortical screw(31.65±1.54 and 31.12±1.35mm),and the difference was significant(P<0.05).There was significant difference between the left and right inclination angles of new S1 cortical screw(5.42±1.62 and 5.40 ± 1.74)and traditional pedicle(24.2 ± 1.72 and 23.8 ± 1.41,P<0.05).The average CT Hu value of ROI around the screw path in three kinds screw placement methods was statistically different in various age groups.The average CT Hu value of ROI around the screw path in new S1 cortical screw and traditional S1 cortical screw in each age group was greater than pedicle screw,and the average CT Hu value of male was higher than female2.There were no statistical difference between the model of this research in the extension and flexion(16.28±1.82)ROM,lateral flexion(12.43 ± 0.97)ROM,torsion(1.98 ± 0.89)ROM,and the previous research model in the extension and flexion(17.29±0.88)ROM,lateral flexion(12.56±0.96)ROM,torsion(2.70 ±0.71)ROM(P>0.05).The stress on sacra 1 screw:The stress of model B and model C on sacra 1 screw in flexion and right bending was(184.96 ± 17.05,189.5 ± 17.47)MPa significantly different from model A(140.32±12.93,85.65 ± 7.98)MPa(P<0.05).The stress of model C on sacra 1 screw in left bending and right torsion was(226.04 ± 20.84,184.00 ± 16.95)MPa significantly different from model A(144.91 ± 13.36,106.72±9.84)and model B(171.28 ± 15.78)MPa,There was significant difference between model C(185.15±19.07)and model A(141.61 ± 13.05)MPa in extension(P<0.05),but there was no difference between model C and model B(P>0.05).Vertebral displacement:There were no significant difference in flexion and extension between modelA,modelB and model C(P>0.05).The vertebral displacement of model C(0.3295 ± 0.030,0.4015±0.037)mm in left and right torsion was significant difference from model B(0.4182 ± 0.038,0.5644±0.042)mm(P<0.05),but there was no difference between model C and model A(P>0.05).There was no significant difference between model B(0.7607 ± 0.024,0.5051±0.044)mm and model C(0.7453±0.026,0.5325±0.046)mm in flexion(P>0.05),but it was significantly higher than model A(0.2909±0.046,0.1829 ± 0.016)mm(P<0.05).The stress on vertebral:The vertebral stress on model B and model C was lower than model A in flexion,extension,lateral bending and torsion.The vertebral stress of model C and model B was significantly smaller than model A(54.84 ± 4.82,60.80±6.05)MPa in flexion(36.10 ± 3.89,49.26 ± 3.68)and extension(33.00 ± 3.60,40.83± 3.34)MP,and model C were significantly lower than those in model B(P<0.05).The vertebral stress of model C and model B in left bending(42.80±4.78,44.38±4.55)and left torsion(29.65 ± 1.88,37.84 ± 1.77)MPa was significantly lower than model A(92.33 ± 3.35,87.66±3.73)MPa(P<0.05).Model B and model C in right bending and right torsion have no difference in vertebral stress(P>0.05).The stress on the cage:The stress on the cage of model B and model C was higher than model A in left bending,right bending,left torsion and right torsion.The stress on the cage of model C and model A were(64.32 ± 2.10,115.03 ± 8.97)MPa significantly lower than model B(178.88 ± 2.49)MPa(P<0.05).The stress on the internal fixation device:Model B and model C was significantly higher than model A in the stress on the internal fixation device(P<0.05).The stress in the left bending on the internal fixation device of model C was(322.94 ± 6.88)MPa significantly higher than model B(291.85 ± 14.35)MPa,and model C in the right torsion(139.58 ± 10.48)MPa was significantly lower than model B(184.00 ± 8.43)MPa(P<0.05).There was no significant difference in the stress of internal fixation device of three models in left torsion(P>0.05).The stress on the new S1 and the traditional S1 cortical screws are superior than the traditional pedicle screw in flexion and right bending,while the stress of new S1 cortical screw in left bending and right torsion is better than traditional S1 cortical screw;The left and right torsion of new S1 cortical screw in vertebral displacement was smaller than traditional S1 cortical screw,and both of them showed higher vertebral displacement in left and right lateral bending.We confirmed that the anti torsion ability of new S1 cortical screw was stronger than traditional S1 cortical screw,and was not as stable as pedicle screw in lateral bending.The new S1 cortical screw and traditional S1 cortical screw have lower vertebral stress in flexion,extension,lateral bending and torsion,The stress of cage was higher in left bending,right bending,left torsion,right torsion,and at the same time,the stress of internal fixation device was higher in flexion,extension,left bending,right bending and right rotation.The new S1 cortical screw and the traditional S1 cortical screw can endure large stress.The internal fixation device and cage could afford to the corresponding stress,which could reduce the stress of the vertebral body,and promote the stability of L5/S1 and the fusion of bone graft.Conclusion:1.The new S1 cortical bone screw has higher CT value around the screw path among the three methods of screw placement.The entry point of the bone was dense and hard,and the screw path was easy to expose,the direction was from the inside up to the outside down,and the important iliac blood vessels and lumbosacral plexus could be avoided.The caudal inclination angle of the screw was 28.66±4.91° on the right side,29.31±5.35° on the left side,the anteversion angle was 5.401±1.74 ° on the right side and 5.42±1.62° on the left side,which was more convenient to the screw rod connection of the upper screw.The image anatomical parameters of three kinds of screw placement methods were measured by GE-64 post-processing system,which provided morphological theoretical basis for clinical application of new S1 cortical bone channel screw.2.The new S1 cortical screw and the traditional S1 cortical screw were superior to the traditional pedicle screw in stability and pull-out force,and the new S1 cortical screw was also superior to the traditional S1 cortical screw in anti torsion.The new S1 cortical screw had almost the same effect as the traditional S1 cortical screw,and had advantages in preventing the loosening of S1 screw and the formation of pseudarthrosis.Moreover,the new S1 cortical screw had the advantages of easy exposure,high safety,protection of blood vessels and nerves,good stability and promotion of interbody fusion.Its path was far away from the nerve root and the spinal canal,which could reduce the risk and incidence of the spinal canal and nerve root injury,and alleviate the pressure of spinal surgeons. |
PDF Full Text Request