Effects Of Rotatory Manipulation On Stress And Displacement In Degenerated Lumbar Spine

Objective:1.This study aims to investigate stress distribution and displacement in healthy and degenerated lumbar during simulated lumbar rotatory manipulation(LRM)in the sitting and side lying positions.2.To compare the effects of LRM in normal and degenerative discs and lumbar motor unit to explore the security,rationality and mechanism of LRM.Methods:1.L4/5 FE ModelA three-dimensional(3D)FE model of a functional L4/5 spinal unit was reconstructed from computed tomography(CT)scans of a 32-year-old male volunteer.Mimics software was used to construct the 3D model.Material properties were modified to more accurately represent the degenerated condition,and disc height and the thickness of the endplate cartilage were incorporated.2.Application and Simulation of LSMLRM in the sitting and side lying positions was simulated to rotate to the right They were decomposed by principium of manipulation.The parameter of mechanics was analyzed with ANSYS 14.5 software.3.Validation of the FE modelThe bottom part of L5 was fixed.The moment of force applied at the superior surface of L4 was 7.5 Nm.Model predictions including range of motion and axial displacements were generally in agreement with experimental data from literatures.Results:1.During LRM in the sitting position,(1)The stress of normal and degenerative lumbar mainly locate on the posterior area,and maximum von Mises stress of posterior area was highest in the mildly degenerated lumbar.(2)Stress in a similar distribution within the healthy and degenerated discs was concentrated at the anterior right side of the annulus.There was right-superior disc displacement.Intradiscal pressure(IDP)in the nucleus and maximum von Mises stress in the annulus was highest in moderately degenerated discs.The degeneration decreased the displacement of the lumbar.2.During LRM in the side lying position,(1)The stress of normal and degenerative lumbar mainly locates on the posterior area,and maximum von Mises stress of posterior area was highest in the moderately degenerated lumbar.(2)Stress in a similar stress distribution within all discs was concentrated at the anterior right side of the annulus.Maximum von Mises stress was highest in the moderately degenerated annulus,and IDP was higher in moderately degenerated discs than in mildly degenerated discs.The displacement of the right side of the disc was larger than that of the left side.The healthy lumbar was displaced the most.3.The stress of discs and posterior structure were higher during LRM in the sitting position than during LRM in the side lying position.Mises stress of posterior area was highest in the mildly degenerated lumbar during LRM in the sitting positions while it was highest in the moderately degenerated lumbar during LRM in the lying positions.The degeneration increased the stress of discs and decreased the displacements during these LRM.Conclusion:1.During LRM in the sitting position,(1)the manipulation cannot make the protruded disc come back.(2)LRM should be used with caution in patients with moderately compromised discs,since high IDP and maximum von Mises stress in the annulus could lead to potential rupture and lumbar disc herniation.Injury was more common on facet joint and arch of vertebra in mildly degenerative lumbar.(3)the displacement caused by LRM may be the major contributor to its beneficial effect.2.During LRM in the side lying position,(1)the manipulation is safe for degenerative discs.However,the disc and posterior area in moderately degenerative lumbar were subject to higher stress.(2)Displacement of discs and vertebras made the nerve away from the relative structure to relieve the pain,but the therapeutic approach towards treating patients with different degrees of disc degeneration should be individualized.3.Stress in the disc of the moderately degenerated lumbar increased dramatically,suggesting caution when treating patients with moderately compromised discs during LRM in the sitting and side lying positions.That nerve roots and disc were separated completely or incompletely may be the mechanism of LRM.It still needs further discussion and quantitative studies for better technique scheme,safeness,rationality and effectiveness.