| Objective:For better understanding of sacral screw fixation of the anterolateral 2 pull-out strength and pull-out process in the sacral stress distribution through Biomechanical tests, to compare the S2,1 anterolateral intensity and the sacral damage around the screw after the pull out,and to provide an effective theoretical basis for it's clinical application and postoperative clinical evaluation.Methods:6 adult sacrum fresh specimens from the Department of Jilin University Norman Bethune Medical Anatomy Department, all male, aged between 25-45. Sacral soft tissue is removed, specimens have been considered by the naked eye to exclude abnormal and pathological situations in order to ensure the quality of bone structure. Dry sacral specimens are obtained from the Department of Jilin University Norman Bethune Medical Anatomy Department regardless of gender, age, visual observation to exclude a sacral deformities and damage of S1,S2. observation and operation of the dry sacral specimens are carried out before the fresh specimens experiment. The bony sacrum anatomical landmark is located, then the sacrum is truncated at the fusion site, therefore, the morphological characteristics of S1 "pedicle" and S2 "pedicle can be observed.The site of resistance strain gauge is dried by Electric iron and processed according to crafts to facilitate the Paste. An screw is implanted into the "pedicle" of S1,S2 specimens. 502 glue is applied to paste the resistance strain gauge to the corresponding site of the specimens. Insulation adhesive tape is placed under the wire to prevent the electric current, terminal blocks is pasted under the resistance strain gauge. The wire of resistance strain gauge is welt to the terminal blocks,and other wires are welt too. Resistance strain gauge is strictly inspected according to Experimental stress analysis before the test. The specimens are placed on the table of electronic universal testing machine and connected to Shimadzu AG-107A Automatic Control Universal Machine, then a sensor is installed.The specimens are fixed at the bottom and object center of gravity is located.The wires pasted to resistance strain gauge is connected to the bridge arm of the instrument in the form of half-bridge and outside compensation after the pre-set of the specimens.Pre-test should be conducted to eliminate time effect such as bone creep and bone relaxation before the formal test.The rate in the testing machine should be controlled at 50mm/min,the data is collected every 30 second and the relative displacement and strain of the screw and scrum are recorded until the screw is pulled out.Results:Maximum pull-out strength of anterolateral screw of S1 left 401N, the right side of 398N, S2 the left side of 220N, the right side of 230N.Both sides add up to S1(342±60)N ,S2 (214±13)N.and the strain of the left and the right side of the center line is obtained respectively from the S1 vertebrae, S2 vertebrae, S3 vertebrae during the pull out. strains of Articular surface of bilateral superior articular process in S1 and bilateral sacral laminectomy in S2 is also obtained.Conclusion:1.S2 "pedicle" anterolateral screw fixation is feasible,For the safety of screw placement, relatively accurate data can be obtained in terms of Anatomical structure, needle point, angle, length of nail and its biomechanical tests.2.There is a significance difference of Axial screw pull-out strength between S1 and S2"pedal". The pull-out strength of S2 is lower than that of S1.There is no significance difference between both sides of S1 and S2.3. S2 "pedicle" screws have a stress impac t to the surrounding bones in the pull-out process experiments show that it will not produce damage to the surrounding sacrum.Anterolateral screw is in line with biomechanical principles. |
PDF Full Text Request