Research And Development On Lumbar Posterior Dynamic System

To date, spinal fusion is a major method for spine degenerativediseases. However, drawbacks of this classic surgery have becomeprominent increasingly. Such as Pseudarthrosis, activity lost in fusionsegment, crista iliaca complications after bone graft, especially theincreasing Adjacent Segment Degeneration (ASD) diseases. Now moreand more expectations have been put on spinal non-fusion technology andmotion preservation device, and such technologies are developing rapidly,including total disc replacement (TDR), posterior dynamic fixation systemetc., part of them have been conducted in clinical trials and obtainedencouraging result. The core idea of non-fusion technology is not onlyremoved the spinal degeneration sources, but also maintain the normalspinal function. Non-fusion technology requires the devices providepatients with a security, stable capability, free activities and lasting durability after implantation.Lumbar flexion-extension activity is the largest and one of the mostimportant physiological activities of spine. The study of lately reportedinstantaneous centre of rotation (ICR) confidence interval and positiondistribution have a certain relationship with cervical and lumbar pain, sothe importance of ICR becomes more notable.The pedicle trajectory data are the important reference material forposterior dynamic fixation system design. New non-fusion device willsimulate the movement and activities of normal spine perfectly by usingthe data. And with regard to spinal degenerative disease diagnosis, it canalso give clinicians a reference.PartⅠ: The distribution of instantaneous centre of rotation andthe trajectory of the point of pedicle screw insertion in lumbarflexion-extension motionObjective: To obtain instantaneous centre of rotation(ICR) and the pointof pedicle screw insertion(PPSI) trajectory by researching lumbar flexionextensionmotion for design new spine non-fusion technology.Method: 61 healthy volunteers, there were 31men and 30women, theaverage age was 27.8±7.1years (range,19~43 years). Men average heightwas 178.5±4.6cm (range,174~190cm). Women average height was164.4±3.3cm (range,157~168cm). From lumbar flexion-extension X-ray,first we measured the ICR position and described the ICR distributionmap. Second we identified the PPSI trajectory by the displacement valueof PPSI, the angle of oblique(AOB) and rotation radius. The data between men and women have been analyzed by statistic method.ResulResult: Although there are significant differences that men's height andL2-L5 upper-endplate posterior-anterior width were larger thanwomen's(P<0.01), the ICR and PPSI values didn't be influenced(P>0.05).In posterior-anterior direction from L1 to L5, lumbar flexion-extensionmotion ICRs were at the middle of the lower vertebral endplateapproximately, and with a trend to became more posterior. In cranialcaudaldirection from L1 to L4, ICRs were near the upper-endplate andtended to go down to the lower vertebral endplate, but L5 ICR returned tothe mid of the disc. In sagittal plane, the PPSI of each lumbar level movedfrom posterior inferior to anterior superior with an arc trajectory. The PPSIdisplacements and the AOB were increased from L1 to L4. However, thetwo value decreased in L5. The rotation radius had no relationship withlumbar sequence.Conclusion: Lumbar flexion-extension motion has the particularity andregularity prompt us that different lumbar level non-fusion surgery needdifferent device which have the motion parameter characteristics of thelevel, then we can reconstruct the spine function better.Part II: New posterior dynamic fixation device design andprocessingBased on the partⅠexperimental results and comprehensive analysisof the characteristics and drawbacks of current dynamic posterior fixationdevice design, we design an innovative sliding posterior fixation. Thisdevice has many innovative advantages that it has a precise trajectory simulation of physiological spine and can be implanted more segments,and can be combined with the posterior disc replacement device to use, iteasier to operate and so on. Then we finished engineering drawing,structural strength finite element analysis and sample processing.