The Design Of Anterior Transpedicular Screw Internal Fixation System For Upper Thoracic Spine And Its Biomechanics Research

Part Ⅰ The study of relevant anatomy parameters from imaging for the design of anterior transpedicular screw internal fixation deviceObjective. Measured the related anatomic parameters from the radiography of upper thoracic spine to provide comprehensive data, which would be refereed for the design of anterior transpedicular screw internal fixation internal fixation deviceMethods. The CT data of 20 cases adult physical check-ups patients, which included the segment of spine from C7 to Th5, was collected. Then each case’s CT data was imported into the Mimics software by the DICOM formatted for 3D reconstruction. The related anatomic parameters for the design will then be measure in Mimics software, and finally statistical analysis for the obtained data.Results. Vertebral height range from 15.4 mm to 16.9 mm. The VBAA-LD range from 17.4 mm to 21.7 mm, and the VBAA-SD range from 4.3 mm to 6.5 mm. The depth of the vertebral corresponding to the VBAA was about 13.1 mm ～20.3 mm. On the median sagittal plane, The VBSA-LD across three vertebral body was about 54.4 mm to 54.8 mm, and the VBSA-SD was about 1.4 mm to 2.0 mm, The Cobb angle was range from 7.2°to 9.0°. The VBSA-LD across 4 vertebral body was about 73.5 mm, the VBSA-SD about 2.5 mm, and the Cobb angle of Thl-4 was about 9.9°. The VPW-I was about 1.8 mm～4.0 mm, and the VPW-O was about 5.2 mm～8.9 mm. The VPH-I was about 4.3 mm-5.3 mm, and the VPH-O about 6.7 mm～11.4 mm. The length of vertebral pedicle was about 35.8 mm～38.0 mm. The distance from PPSI to superior endplate was about 57 mm～7.6 mm, to the inferior endplate was about 9.4～9.8 mm, and to the median sagittal plane was about 2.4 mm-4.0 mm. The TSA is about 12.3°～32.1°, and The SSA was about 100.7°～103.6°.Conclusion. The obtained data have certainly practical and could be referred for internal fixation of design.Part II The design of anterior transpedicular screws plate system for upper thoracic spine and its finite element analysisObjective. Design each component of the anterior transpedicular screws plate system base on the data of Part Ⅰ, then make simulation analysis through software to preliminary evaluation mechanical property of each component of the fixation system.Methods. Using frequency distribution method to analysis in-depth of the data obtained in Part I to provide accurate data for the design of the internal fixation system. The height of vertebral body was correlate with the height of fixed plate. The depth of the vertebral body was correlate with the length of the vertebral body screw. The vertebral body axial arc was correlate with the width and axial arc of the fixed plate. The multi-vertebral body sagittal arc was correlate with the height and sagittal arc of the fixed plate. The width of vertebral pedicle is correlate with the diameter of pedicle screws. The point of pedicle screw insertion and the angle of pedicle axial line was correlate with the pedicle open slot on the fixed plate. Based on those depth-analysis data, through the computer software to design the parts of model, each component model of the fixation system was design through software. Then made a simulation analysis through software to preliminary evaluation mechanical property to evaluate whether the mechanical properties of each components of the system meet the requirement of actual needed.Results. According to the anatomical data, each components model of anterior transpedicular screw internal fixation system was designed. The main components of internal fixation system was simulated through software, and all simulation results shows that the mechanical properties of each components of the system meet the requirement of actual needed.Conclusion. According to the anatomical data, various components of the anterior thoracic spine pedicle screw internal fixation system could be successfully design. By computer simulation, the main components of internal fixation system could meet the requirements of the human body activity’s needed.PartⅢ Comparison of the pullout strength between three types of screws at upper thoracic spineObjective. To compare the pullout strength between three types of screws at upper thoracic spine.Methods. Six embalmed cadavers specimens, which contain the entire structure from C7 to Th5 and exclude osteolysis and other structural lesions, were harvested. Each six vertebra from Thl to Th4 were included in the experiment. Experiment testing was divided into three groups:The group of anterior transpedicular screw (ATPS), The group of posterior transpedicle screw (PTPS) and the group of anterior vertebral body screw (AVBS). Randomization process was carried out on the specimens of each vertebra before experiment. Around each vertebral pedicle as two different numbers to participate in the randomization. According to the random results, inserted either ATPS or PTPS in two side of the pedicle, and inserted a AVBS in the front of the same vertebral body. The screw axial pullout test was carried out on mechanics testing machine. Recorded each screw length and peak pullout force, then make statistical analysis for the data.Results. In either group of ATPS and PTPS, the screw length and peak pullout force of each vertebral body (Thl-Th4) was statistically significant different (P<0.05). The screw length and peak pullout force of each vertebral body (Thl-Th4) in AVBS group was no statistical significance difference (P>0.05). After merging the data in each group, the screw length and peak pullout force between groups was statistically significant different (P<0.05). The length of screw in ATPS groups, PTPS groups and AVBS groups was (37.0±1.2)mm, (29.6±1.1)mm and (17.03±1.4)mm, respectivly. The peak pullout force was (382.2±12.4)N, (290.3±11.7)N and (135.5±7.1)N, respectivly. There was significant correlation between the length of screw and peak pullout force (r =0.997, P=0.000).Conclusion. The length of screw was positively correlated with peak pullout force, where an increase of the length of a screw will increase the amount of peak pullout force. At upper thoracic spine, the peak pullout force of ATPS was greater than PTPS and AVBS. The study documented that ATPS had a better biomechanical stability which would help to improve the stability of the internal fixation system.PartVI Comparison of the pullout strength between two types of anterior internal fixation devices at upper thoracic spine.Objective. To compare the pullout strength between anterior transpedicular screws-plate system (ATPSPS) and anterior vertebral body screws-plate system (AVBSPS) at upper thoracic spine.Methods. Eight embalmed cadavers specimens which contain the entire structure from C7 to Th5 were collected. The specimens were randomly divided into two groups (ATPSPS and AVBSPS), each group contain four specimens. The ATPSPS and AVBSPS were implanted separately in each group. The vertical pullout tests,on the mechanical testing machine then was carried out. The total screw length and the peak pullout force was recorded and compared between groups.Results. The mean total screw length of ATPSPS was greater than AVBSPS (P<0.05). The mean peak pullout force of ATPSPS was greater than AVBSPS (P<0.05). The mean total screw length of the system in ATPSPS was (114±4.0)mm and the peak pullout force was (1242±79.6)N. In AVBSPS, the mean total screw length of the system was (69±4.4)mm and the peak pullout force was (637±12.8)N. Pearson correlation coefficient analysis showed that the mean total screw length of the system was positive correlation with the peak pullout force (r=0.987, P=0.000).Conclusion. The pullout strength of ATPSPS is larger than AVBSPS, showing a better biomechanical stability.Part Ⅴ Comparison of the fixation rigidity between three types of anterior internal fixation devices at upper thoracic spine.Objective. To compare the fixation rigidity between anterior transpedicular screw-plate system (ATPSPS), posterior transpedicle screw-rod system (PTPSRS) and anterior vertebral body screw-plate system (AVBSPS) at upper thoracic spine.Methods. Twelve embalmed cadavers including C7 to Th5 were randomly divided into three groups, each group contained 4 specimens. Three groups of specimens were randomly assigned to use three different groups of internal fixation devices. Firstly, measured the stiffness of each intact specimens on the direction of axial compression, flexion and extension, and lateral bending. Then measured the stiffness of each specimen which simulated corpectomy of Th2 (damage model) on different direction. Finally, measured the stiffness of each specimen after fixed by anterior internal fixation system. Compared the stiffness on different direction in each group and between different groups.Results. The stiffness in each group of different status was statistically significant different in each direction (P<0.05). There was no statistical significant difference of the stiffness among the three groups of specimens, whether in the intact state or the damage model (P>0.05). The stiffness of three groups in all directions were statistically significant different after instrument fixation (P<0.05). For the stiffness of flexion, there was statistical significant difference between three group (P<0.05), ATPSPS group was greater than the other two groups. For the stiffness of axial compression and extension, there was a statistically significant difference among the three groups (P<0.05), PTPSRS group was greater than the other two groups. For the stiffness of lateral bending, AVBSPS group was smaller than the other two groups, the difference was significant (P<0.05), and there was no statistically significant difference between the other two groups (P>0.05)Conclusion. After fixation, the stiffness was improved in all direction of the specimen. ATPSPS showed largest flexion stiffness, but the stiffness of axial compression and extension was smaller than PTPSRS, and there was no difference between the two groups in lateral bending. AVBSPS showed smallest stiffness in all direction when compared to other two groups. ATPSPS showed a better initial fixation rigidity than AVBSPS.