Disc Degeneration Affects the Multidirectional Flexibility of the Lumbar Spine

Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut.
Spine (Impact Factor: 2.3). 07/1994; 19(12):1371-80. DOI: 10.1097/00007632-199406000-00011
Source: PubMed


An in vitro biomechanical investigation using human lumbar cadaveric spine specimens was undertaken to determine any relationship between intervertebral disc degeneration and nonlinear multidirectional spinal flexibility.
Previous clinical and biomechanical studies have not established conclusively such a relationship.
Forty-seven discs from 12 whole lumbar spine specimens were studied under the application of flexion-extension, axial rotation, and lateral bending pure moments. Three flexibility parameters were defined (neutral zone (NZ), range of motion (ROM), and neutral zone ratio (NZR = NZ/ROM)) and correlated with the macroscopic and radiographic degeneration.
In flexion-extension, the ROM decreased and NZR increased with degeneration. In axial rotation, NZ and NZR increased with degeneration. In lateral bending, the ROM significantly decreased and the NZR increased with degeneration. In all three loading directions, the NZR increased, indicating greater joint laxity with degeneration.

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    • "Mechanical instability is considered related to excessive spinal segmental movement and is confirmed by radiography (Fritz et al., 2005; Beazell et al., 2010). Numerous studies have dealt with changes in segmental movement in relation with structural changes in the disc, which is a finding reported in cases of disc degeneration (Mimura et al., 1994; Li et al., 2011; Ibarz et al., 2013). Panjabi (1992) defined a functional instability as loss of the spine's ability to maintain intervertebral neutral zones under loaded conditions , resulting in pain and disability. "
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    ABSTRACT: The goal of the current study was to investigate potential differences in back and hip extensor muscle activity and hip extension force during prone hip extension (PHE) in individuals with lumbar segmental instability (LSI) and asymptomatic subjects. Thirty-six subjects with LSI and 26 asymptomatic volunteers participated in this study. Muscle activity of the erector spinae, gluteus maximus, and biceps femoris was recorded using electromyography (EMG), and hip extension force was measured by a digital force gauge. Muscle activity was significantly greater in subjects with LSI than in asymptomatic subjects during PHE (p < 0.05). Hip extension force was significantly lower in the subjects with LSI than in asymptomatic subjects during PHE (p < 0.05). These findings suggest that during PHE, subjects with LSI have differences in back and hip extensor muscle activity and hip extension force compared to asymptomatic individuals.
    Manual Therapy 11/2014; 20(3). DOI:10.1016/j.math.2014.11.002 · 1.71 Impact Factor
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    • "Yet, experimental and computational works inferred that the disc morphology also affects the spinal compliance [8] [9]. Indeed, independently of the disc's chemical composition or integrity, it was shown that the larger the cross-sectional area of an intervertebral disc, the stiffer its response and that the thicker the IVD, the more compliant its behavior. "
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    ABSTRACT: Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without efficient normalization of the stiffness with respect to morphology. Moreover, although the behavior of soft tissues is highly non-linear, only linear normalization protocols have been defined for the disc. Thus, the aim of this work is to propose a non-linear normalization based on finite elements (FE) simulations and evaluate its impact on the stiffness of human anatomical specimens of lumbar IVD. First, a parameter study involving simulations of biomechanical tests (compression, flexion/extension, bilateral torsion, bending) on 20 FE models of IVDs with various dimensions was performed to evaluate the effect of the disc's geometry on its compliance and establish stiffness/morphology relations necessary to the non-linear normalization. The computed stiffness was then normalized by height (H), cross-sectional area (CSA), polar moment of inertia (J) or moments of inertia (Ixx, Iyy) to quantify the effect of both linear and non-linear normalizations. In the second part of the study, T1-weighted MRI images were acquired to determine H, CSA, J, Ixx and Iyy of 14 human lumbar IVDs. Based on measured morphology and pre-established relation with stiffness, linear and non-linear normalization routines were applied to the compliance of the specimens for the quasi-static tests. The stiffness variability prior to and after normalization was assessed via coefficient of variation (CV). The FE study confirmed that larger and thinner IVDs were stiffer while the normalization strongly attenuated the effect of the disc geometry on its stiffness. Yet, notwithstanding results of the FE study, the experimental stiffness showed consistently higher CV after normalization. Assuming that geometry and material properties affect the mechanical response, they can also compensate for one another. Therefore, the larger CV after normalization can be interpreted as a strong variability of the material properties, previously hidden by the geometry's own influence. In conclusion, a new normalization protocol for the intervertebral disc stiffness in compression, flexion, extension, bilateral torsion and bending was proposed, with the possible use of MRI and FE to acquire the discs' anatomy and determine the non-linear relations between stiffness and morphology. This may be useful to relate the disc's mechanical properties to its degree of degeneration.
    Journal of Biomechanical Engineering 03/2014; DOI:10.1115/1.4027300 · 1.78 Impact Factor
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    • "The results of these studies vary considerably. Similarly to Kirkaldy-Willis and Farfan [29], some authors report instability during the early stages of degeneration [30] [31] while others rather show the opposite [32] [33]. These partial contradictive results are probably enforced by the relative small number of specimens. "
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    ABSTRACT: The study of the mechanical properties of the annulus fibrosus of the intervertebral discs is significant to the study on the diseases of lumbar intervertebral discs in terms of both theoretical modelling and clinical application value. The annulus fibrosus tissue of the human intervertebral disc (IVD) has a very distinctive structure and behaviour. It consists of a solid porous matrix, saturated with water, which mainly contains proteoglycan and collagen fibres network. In this work a mathematical model for a fibred reinforced material including the osmotic pressure contribution was developed. This behaviour was implemented in a finite element (FE) model and numerical characterization and validation, based on experimental results, were carried out for the normal annulus tissue. The characterization of the model for a degenerated annulus was performed, and this was capable of reproducing the increase of stiffness and the reduction of its nonlinear material response and of its hydrophilic nature. Finally, this model was used to reproduce the degeneration of the L4L5 disc in a complete finite element lumbar spine model proving that a single level degeneration modifies the motion patterns and the loading of the segments above and below the degenerated disc.
    Journal of Applied Mathematics 01/2014; 2014(6):1-15. DOI:10.1155/2014/658719 · 0.72 Impact Factor
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