| Anterior Cervical plate (ACP) and lumbar posterior transpediclar fixation are widely used clinically. Now the anterior cervical unconstrained plate and lumbar conical pedicle screw used more popular, this test evaluated anterior cervical unconstrained plate, lumbar conical pedicle screw and pedicle screw revision's biomechanics characteristic.Part 1 ACP was widely used in the treatment of degenerative, traumatic and tumor condition. Now the cervical plate has developed to the third generation: unconstrained plate, which has the ability of dynamic compression. On the other hand, there was quarrel that this type plate may over compressed and has disadvantage to the posterior elements. This experiment was done on the fresh cervical specimen whose C4-5 ACDF was done, and the load transverse between graft and plate was analyzed. Objective: To analyze biomechanics difference between constrained and unconstrained ACP. Method: 6 fresh normal fresh cadavers (C2-T1) were done with C4-5 disc discectomy, compression sensor and strain gauge were used to measure the compression load through the graft and plate. Test sequence was: without plate, unconstrained plate, constrained plate, constrained plate with 1mm absorption, unconstrained plate with lmm absorption. Result: (1) The graft load decreased with the sequence from without plate, unconstrained plate to constrained plate group, and the difference was significant(p<0.05). When 1mm absorption took place, the load transversed through the graft was significantly higher in unconstrained plate than in constrained group (p<0.05). (2) No matter whether there was absorption, load transversed through the plate in constrained plate was higher than in unconstrained plate group. (3) After absorption, the load of posterior elements all arises, especially for the unconstrained plate. (4) Anterior plate bear bending strength except for the compression strength and no matter whether there was absorption, for the constrained plate the bending strength was higher than unconstrained plate. Conclusion: More load transverse through the graft with the use of unconstrained plate in the condition of single level ACDF, which is benefit to the union of the graft. When absorption or collapse occurred to the graft, it was found that more strength transverse though the posterior elements with the use of unconstrained plate. For the reason of rigidity, there was more bending strength for constrained plate, and this strength was with the risk of bending plate, so enough strength was essential for the constrained plate. Part 2 Pedicle screw (PS) fixation is one of the most widely used posterior fixation on the treatment of thoracolumbar and lumbarsacral disease. If the load was too early or too high, there was the risk of breaking or loosing of the screws. Sometimes, the revision is necessary. Now there was two type screw of conical and cylindrical PS used clinically. Objective: To compare the biomechanical performance of the conical and cylindrical PS in lower thoracic and lumbar vertebra, and to evaluate the stabilization of revision. Method 54 vertebral specimen was obtained from 6 fresh normal frozen cadavers (T9-L5). The experimental 5.5 mm conical and cylindrical PS were implanted at different side pedicle at random and tested with an MTS machine. The maximal insertion torque and the maximal pull-out strength were measured. Then the revision was done... |
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