Do Bending, Twisting, and Diurnal Fluid Changes in the Disc Affect the Propensity to Prolapse? A Viscoelastic Finite Element Model

Lu, Y M; Hutton, W. C.; Gharpuray, V. M.

doi:10.1097/00007632-199611150-00006

Cited by 200 publications

(94 citation statements)

References 36 publications

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“…This finding may be due to the fact that the annular fibres medial to the pedicles and inclined in the direction of applied axial rotation are shorter contralaterally than ipsolaterally [36] and would thus be strained more highly during torsion. Despite this tendency for endplate tears to propagate contralaterally, radial tears communicating from the nucleus to the disc periphery formed centrally, consistent with the finite element modelling prediction made by Lu et al [37]. The posterolateral disc wall appears to be very robust compared to the posterior when discs are subjected to pure flexion in the sagittal plane, as in the current study.…”

Section: Discussionsupporting

confidence: 90%

The influence of torsion on disc herniation when combined with flexion

2010

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The role of torsion in the mechanical derangement of intervertebral discs remains largely undefined. The current study sought to investigate if torsion, when applied in combination with flexion, affects the internal failure mechanics of the disc wall when exposed to high nuclear pressure. Thirty ovine lumbar motion segments were each positioned in 2°axial rotation plus 7°fl exion. Whilst maintained in this posture, the nucleus of each segment was gradually injected with a viscous radioopaque gel, via an injection screw placed longitudinally within the inferior vertebra, until failure occurred. Segments were then inspected using micro-CT and optical microscopy in tandem. Five motion segments failed to pressurize correctly. Of the remaining 25 successfully tested motion segments, 17 suffered vertebral endplate rupture and 8 suffered disc failure. Disc failure occurred in mature motion segments significantly more often than immature segments. The most common mode of disc failure was a central posterior radial tear involving a systematic annulus-endplate-annulus failure pattern. The endplate portion of these radial tears often propagated contralateral to the direction of applied axial rotation, and, at the lateral margin, only those fibres inclined in the direction of the applied torque were affected. Apart from the 2°of applied axial rotation, the methods employed in this study replicated those used in a previously published study. Consequently, the different outcome obtained in this study can be directly attributed to the applied axial rotation. These inter-study differences show that when combined with flexion, torsion markedly reduces the nuclear pressure required to form clinically relevant radial tears that involve cartilaginous endplate failure. Conversely, torsion appears to increase the disc wall's resistance to radial tears that do not involve cartilaginous endplate failure, effectively halving the disc wall's overall risk of rupture.

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Section: Discussionsupporting

confidence: 90%

The influence of torsion on disc herniation when combined with flexion

2010

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“…The ratio of fiber volume to the surrounding ground substance volume changed from 5% to 23% from the inner to outer layers. 22 Facet cartilage layers were modeled using hexahedral elements. The facet joint was assumed to have a frictionless contact.…”

Section: Methodsmentioning

confidence: 99%

Instantaneous center of rotation behavior of the lumbar spine with ligament failure

Alapan

Demir

Kaner

et al. 2013

SPI

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Object The goal of this study was to investigate the effect of ligament failure on the instantaneous center of rotation (ICR) in the lower lumbar spine. Methods A 3D finite element model of the L4–5 segment was obtained and validated. Ligament failure was simulated by reducing ligaments in a stepwise manner from posterior to anterior. A pure bending moment of 7.5 Nm was applied to the model in 3 anatomical planes for the purpose of validation, and a 6-Nm moment was applied to analyze the effect of ligament failure. For each loading case, ligament reduction step, and load increment, the range of motion of the segment and the ICR of the mobile (L-4) vertebra were calculated and characterized. Results The present model showed a consistent increase in the range of motion as the ligaments were removed, which was in agreement with the literature reporting the kinematics of the L4–5 segment. The shift in the location of the ICR was below 5 mm in the sagittal plane and 3 mm in both the axial and coronal planes. Conclusions The location of the ICR changed in all planes of motion with the simulation of multiple ligament injury. The removal of the ligaments also changed the load sharing within the motion segment. The change in the center of rotation of the spine together with the change in the range of motion could have a diagnostic value, revealing more detailed information on the type of injury, the state of the ligaments, and load transfer and sharing characteristics of the segment.

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“…The orientations of the annulus fibers increased continuously from ± 23° at the anterior side to ± 58° at the posterior side, and the ratio of fiber volume to the surrounding annulus ground substance volume changed from 5% to 23% from the inner layers through the outer layers. 21 The annulus ground substance, nucleus, and cartilaginous endplates were modeled with hexahedral solid elements, and the annulus fibers were modeled with tension-only link elements.…”

Section: Methodsmentioning

confidence: 99%

Load sharing in lumbar spinal segment as a function of location of center of rotation

Alapan

Sezer

Demir

et al. 2014

SPI

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Object The center (axis) of rotation (COR) in the lumbar spine has been studied well. However, there is limited information on the kinetic and kinematic consequences of imposed shift in the location of the COR, although this type of shift can be seen after surgeries using motion preservation or dynamic stabilization devices. The objective of this study was to assess the kinetic and kinematic changes in the lumbar spinal segment due to various imposed CORs. Methods A 3D finite element model of the L4–5 segment was constructed and validated. The segment was loaded under a 7.5-Nm bending moment while constrained to rotate about various imposed CORs in the sagittal and axial motion planes. Range of motion, ligament forces, facet loads, and disc stresses were measured. Results The present model showed an agreement with previous in vitro and finite element studies under the same load and boundary conditions. Range of motion, facet forces, disc stresses, and ligament loads showed a strong association with the location of the COR. Conclusions Acute alterations in the location of the COR can significantly change the load sharing characteristics within the spine segment. The normal location of the COR is a result of the tendency of the vertebra to move in the path of least cumulative resistance.

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Do Bending, Twisting, and Diurnal Fluid Changes in the Disc Affect the Propensity to Prolapse? A Viscoelastic Finite Element Model

Abstract: The results from this study suggest that there are several key factors involved in the initiation and propagation of anulus failure: axial compressive load, bending and twisting, and disc saturation. If one of these is lacking, anulus failure is harder to achieve.

Cited by 200 publications

References 36 publications

The influence of torsion on disc herniation when combined with flexion

The influence of torsion on disc herniation when combined with flexion

Instantaneous center of rotation behavior of the lumbar spine with ligament failure

Load sharing in lumbar spinal segment as a function of location of center of rotation

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