Effect Of Intervertebral Disc Decompression On Vertebral Rotation

Objectives:To investigate simple intervertebral disc decompression and the effect of reducing vertebral rotation torque in the direction of axial rotation.Methods:6 fresh adult porcine were involved and made into 36 specimens which was consist of 2 adjacent vertebral bodys and 1 intervertebral disc from T8/9 to L5/6.The specimens were embedded with polymethylmethacrylate(PMMA).Then the specimens were fixed on the Instron tensile torsion test machine.In the first test,the caudal vertebrae was immobilized,while the cranial vertebrae was rotated 6° counterclockwise and clockwise.Repeat the above loading test 3 times.The maximum torque was recorded in both direction.After that,the initial disc decompression was made by incising the annulus fibrosus for 1cm in the right posterior portion.Then the second test(the same procedure as the first test)was made and the maximum torque was recorded.The third test was made after a further dic decompression(2.5cm).The torque decrease after the decompressions in both direction was analyzed by spss20.Results:The average maximum torque required for counter clockwise rotation of the 12 level intact specimens vary from 7.42Nm to 14.22Nm,with an average of 12.43Nm and a moderate positive correlation with the disc level(P<0.05,r=0.781).The maximum torque required for counterclockwise rotation were respectively 12.43±3.71,10.44±3.32 and 8.12±2.90 Nm in the 3 tests;The counterclockwise were respectively12.57±4.12,10.94±3.81 and 7.97±3.52Nm.The mean values of the maximum torque decline caused by the two decompression in the counterclockwise direction were 2 ± 0.81 and 2.32±1.56 Nm.In clockwise direction 1.63 ± 0.74 and 2.97±1.90 Nm respectively.The largest torque decreased obviously by the further decompression in the clockwise direction,with an average value of(2.97 ± 1.90)Nm,significantly higher than that by the initial decompression in the same direction(LSD-t=4.235,P<0.05),also significantly higher than that in the opposite direction(LSD-t=2.059,P<0.05).Conclusions:The pressure of the nucleus pulposus or the integrity of the fibrous ring,rather than the fibrous ring itself,plays a more critical role in the axial rotation of the vertebral body.Simple disc decompression can significantly reduce torque required for axial deflection of the vetebral.And the effect of simple disc decompression to reduce the torque follows the law of diminishing.