The Study On The Biomechanics Effect Of Different Torsion Torque On The Adjacent Segment After Lumbar Spinal Fusion

Objective:To evaluate the effects of small different torsion torques on ntradiscal pressure(IDP)and pressure in the facet joints(PFJ)on the upper adjacent segment before and after lumbar spinal fusion.This study was performed by a cadaveric porcine spine motion segment experiment.Methods: Six lumbar porcine cadaveric motion segments(L1-S1)were loaded in the neutral position with 300 N of axial compression. Intranuclear pressure(L3/4)and pressure in the facet joints(L3/4) measurements were then obtained at 0, 1.0, and 2.0 Nm of torsion before and after lumbar spinal fusion(L4/5). T-test was adopted to compare the changes of pressure in facet joints and intradiscal pressure before and after different programs.One-way classification(ANOVA) was adopted to compare the changes of different sample. ρ<0.05 represents that the difference was of significance.Results:1. IDP:Along with the increasing of loading torque, IDP of fusion group and non-fusion group were both gradually rise from a relatively stable state to achieve to another relatively stable state until the end of the loading.(1) Non-fusion group: The changes of instantaneous value of IDP increased after loading,but there was no statistically significant difference in IDP with different torsion torques(T=1N.m、T=2N.m).(2) Fusion group: The changes of instantaneous value of IDP also increased after loading,and with the increase of torsion torques,the IDP showed a rising trend. The changes of IDP value in different torsion torques(T=1N.m、T=2N.m) had statistically significant difference(ρ=0.023).(3)Comparison before and after fusion: In the same loading condition torsion torque( T=1Nm), the changes of IDP value in the fusion group and non-fusion group has no obvious statistically significance difference. While, It has statistically significant difference when loading 2Nm torsion torques in the two groups(ρ=0.034).(4) No matter non fusion group or fusion group, the comparison of samples has no difference.2. PFJ: As the results of infrared scanning pressure sensitive piece revealed, in the wake of the increase of torsion torque,both non fusion group and fusion group the PFJ become more and more higher. The larger torsion torque, the higher PFJ.(1) Non-fusion group: The changes of value of PFJ increased after loading, and there was statistically significant difference in PFJ with different torsion torques(T=1N.m、T=2N.m)(ρ=0.032).(2) Fusion group: we also obtained the same result in the fusion group and also founded statistically significant difference in the PFJ value with different torsion torque(T=1N.m、T=2N.m)(p=0.01).(3) Comparison before and after fusion: No matter loading 2Nm torsion torques or 1Nm torsion torques, the changes of PFJ value in the fusion group and non-fusion group both has statistically significant difference(T=1Nm,ρ=0.046; T=2Nm, ρ=0.047).(4) No matter non fusion group or fusion group, the comparison of samples has no difference.Conclusions:1.The IDP at the upper adjacent segment has not obvious changes in the non-fusion group;while the IDP in the fusion group increase with the torsion torque increasing.2.The PFJ increase with the torsion torque increasing in non-fusion group and fusion group.3.The increasing of adjacent IDP and PFJ maybe are important causes for the adjacent segment degeneration after fusion.