| Background：For thoracolumbar fractures, there are a lot of fixed way, but, atpresent intermediate screws in short segment pedicular fixation is minimal damage,cost less, and fixed tightly. the short segment pedicle instrucmentation（SSPI）andSSPI for intermediate biomechanics control research more,but,because the vertebraeshape show diversification after fracture, there are few biomachic research for the hurtvertebrae pedicle screw.. the various screw way for vertebral fracture will make adifferent influence for the fixed segment stability.Objective: Through in vitro biomechanics experiment, comparing the influenceby different pedicle screw in fractuer vertebrae for the stability of the fixed segmentand control strength. At the same time, keep record of the stress changes with upperand lower vertebrae, observe the force changes in the fixed segment and reflect theinfluence of different fixation methods on fractured vertabral height lost again.Material and Mehtods: Collect16pig(110~130kg,7~8monthes olds）freshthoracolumbar specimens from T13~L3, and divided into4groups randomly:Group A:contract（without furacture）;Group B: intermediate screw with short size（Φ6.0×3.0）;Group C: inclined intermediate screw with long size（Φ6.0×4.0）；Group D:intermediate screw with long size（Φ6.0×4.0）. After vertebral endplate pre-injury,Then we used a mass-drop technique to create the A-type fracture model within GroupB、C、D．After a fracture was created，the immediate6-screw construct were used torealign and stabilize the specimen．Three dimensional motions of segment T14~L2were measured on a spinal three motion test machine and record the range of motion.For getting the relative stability of the there construct，we comparaed the ROM of thethere construct to the intact．Complete set out vertebraes within intermediate screwand within normal pedicle screw. Choose4vertebraes from Group A setting Group a,choose4intermediate screw vertebraes from Group B setting Group b, choose4intermediate screw vertebraes from Group C setting Group c, choose4intermediate screw vertebraes from Group D setting Group d. Then experiment pull-out strengthtest,compare the mean holding strength in each group.Results:1. Compared the stability of there types intermediate screw in thoracolumbar：Onthe basis of the ROM measurement results:there were not significant differences inROM between Group B and Group C. Compare Group B、Group C with Group D,there were significant differences,except flex and extend. Compare Group B、GroupC、Group D with Group A, there were significant differences in any direction.2. Compared the force changes of there types intermediate screw inthoracolumbar：On the basis of the stress changes of each measurement point: duringthe flexion or extension, compare Group B、Group C with Gourp D, there weresignificant differences in measurepoint5. During the right or left bend, compareGroup B、Group C with Gourp D, there were no significant differences in eachmeasurepoint.3. Comparison of pull-out strength with intermediate screw: compare Group b、Group c with Gourp d, the mean of Gourp d is more powerful than Group b andGroup c. there were significant differences. compare Group b with Gourp c, therewere no significant difference. the mean of Gourp a is more powerful than Group b、Group c and Goup d, has Statistical significance.Conclusion:1. Inclined intermediate screw fixation is more stability than intermediate screwwith long size or short size fixation.2. During the flexion or extension, the force changes in the front midpoint ofupper vertebrea within inclined intermediate screw fixation significantly less thanintermediate screw with long size or short size fixation. In each direction of activities,the force changes of upper vertebrae are more than the lower vertebrae.3. Inclined intermediate screw pull-out strength is more powerful thanintermediate screw with long size or short size... |
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