Hole Preparation Techniques For Transpedical And Related Biomechanics Research

Objective: The thoracqlumbar vertebra fracture is usually treated by transpedicle screw fixation. Since its effects are correlated to the hole preparation techniques for transpedicle , This study was made to search the hole preparation method for transpedical internal fixation in thoracolumbar to increase accuracy of pedicle screw placement , And test its biomechanical strength and stiffness characteristics to provide some biomechanical evidence for better clinical operation and improve quantity of pedicle internal fixation, and decrease complications. methods: Firstly, to selecteing thoracolumbar spine specimen from 6 adult fixture cadavers, including 12 functional spinal units. Then, divided into two groups : to bite away 5mm area of the posterior cortex in the study group and to remain the posterior cortex in the control group. Secondly, we fixed the models with the bilateral Steffee instrumentation with 6mm diameter pedicle screws implanted in 5-15 ?direction. Finally, testing the diffference betwee two groups in strength, stiffness and stability. We design two study groups, one group bite away 8mm area of the posterior cortex, another is 5mm, in pullout testing. Results: To biomechanically compare the flexion-extension, lateral bending, axial compression and axial torsion with the control group, the system analyzing results demonstrate that strength have no significant difference (P>0.05) . but significant difference (P<0.05) was found in pull-out strength between the group to bite away part of the posterior cortex and the group to remain the cortex if the scope of biting away the cortex exceed the screw's diameter. The pull-out strength of study group compared with control group , is lower by 12- 1 5% . Conclusion: To analyse strength, stiffness between two groups,praparing hole for pedicle by biting away part of the posterior cortex have no significant different between with control groups, the test show that it is a safe, simple and effective method for stabilizing a spinal motion segment. But should notice the influence with pullout testing, the scope of biting away the posterior cortex should not exceed the screw's diameter.