Distribution of instantaneous rotation centre and the trajectory of the point of pedicle screw insertion in lumbar flexion-extension motion

English Keywords:Lumbar  Spine non-fusion  Instantaneous centre of rotation  Pedicle

English Abstract:

  【Abstract】 Objective：To investigate the instantaneous centre of rotation（ICR） and the point of pedicle screw insertion（PPSI） trajectory during lumbar flexion-extension motion and to provide the data for design of spine non-fusion technique.Method：61 healthy volunteers（31 males and 30 females） with the average age of 27.8±7.1 years（range，19-43 years） were included in this series.The average height for male and female was 178.5±4.6cm（range，174-190cm） and 164.4±3.3cm（range，157-168cm） respectively.Based on lumbar flexion-extension X-ray，the ICR position and distribution was first demonstrated，then the PPSI sagittal displacement， angular variation，rotation radius and flexion-extension ROM during flexion-extension movement were measured.The data between male and female were analyzed statistically.Result：Although greater height and greater L2-S1 upper-endplate posterior-anterior width for males than females（P<0.01），the ICR distribution and PSAP displacement at each segment did not show sex-related difference（P>0.05）.In posterior-anterior direction from L1 to L5，ICRs during lumbar flexion-extension motion lied approximately in the middle of the upper-endplate of lower vertebra with a backward tendency.In cranial-caudal direction from L1 to L4，ICRs moved from the middle of the disc to the upper-endplate of lower vertebral，but ICR of L5 returned to the middle of the disc.In sagittal plane，the PPSI of each level moved from inferoposterior to superoanterior with an arc trajectory.The PPSI displacements and angular variation increased from L1 to L4，however，these two decreased in L5 simultaneously.The rotation radius had no relationship with lumbar segment.Flexion-extension ROM from L1/2 to L5/S1 increased gradually.Conclusion：Lumbar flexion-extension motion is characteristics and regular which indicate that non-fusion surgery at different lumbar level should be associated with relative device get better reconstruction of the spine physioactivity.