The Design And Mechanical Testing Of Lumbar Transpedicular Dynamic Fixation System

BackgroundThe patients who have light and initial lumbar disc degenerative disease failed in formal strict conservative treatment after six months at least, often be suggested surgical operation.Lumbar disc herniation often be operated with removing the nucleus pulposus only, for those of spinal stenosis or spondylolisthesis instability caused by serious lumber disc degeneration, the best choice is spinal fusion, fixation is the common and effective method of treating with lumbar instability, whereas increasing stress of the adjacent segments, which may accelerate their degeneration. Non-fixed lumbar spinal fusion, which is also known as dynamic stabilization, it is effective method that improving lumbar stress transferation, relieving pain and preventing the occurrence of degeneration of adjacent joints, but keeping the other normal vertebrals activity.ObjectiveTo develop a new lumbar transpedicular dynamic fixation system, clarifying its composition and structure, the principle features. To investigate its clinical feasibility by testing the mechanical stability.Methods1 Design the new lumbar dynamic fixation system:Measure twenty normal persons'L1-L5 vertebral segment pedicle width, height and length of the pedicle channel (from pedicle edge cortex center to vertebral bottom margin midpoint),and test L1-L5 segment activity. Basing on lumbar imaging data, we put forward design ideas, and draw blueprint. Watson company is commissioned to manufacture the sample. 2 The mechanical testing of new lumbar dynamic rod comparing with the traditional rigid rod:Choose five dynamic rods and five rigid bars randomly as strong subjects, impose on a different load by the universal testing machine, record the dynamic rods'displacement change and force change curve,combine triangle function table, calculate degree of flexion,handle the data in the computer,compare the parameters difference .Results1 From top to bottom, lumbar pedicle height reduces gradually, the pedicle width widens increasingly , the change of pedicle channel length is insignificant, the activity of lumbar segment increases little by little, the largest segment of activity is L4/L5.2 Under 200N physical load, the dynamic rods group's flexion motion range is 6.6°±1.1°,the rigid bars group's flexion change is average 2.8°。There are significant statistical difference in the range of motion between dynamic rods group and rigid bars group (P <0.05). Conclusion1 The design and fabrication of the fixation system comply with lumbar pedicle structural features and the physiological activity characteristics, retaining a certain degree in the flexion and extension,lateral bending,side spin and other activities, which is a new lumbar posterior transpedicular dynamic fixation system.2 Under 200N physical load , the dynamic rod's flexion motion range 6.6°±1.1°, range of motion is 0°～15.4°, better than the traditional rigid bar, approaching normal vertebrals activity.