Effect of loading frequency on trans-endplate nutrition across the intervertebral disc: A force-controlled unconfined compression experiment

Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic finite element model of intervertebral disc and use it to investigate the confounding effect of material properties and loading conditions on the disc deformation and pore pressure. An axisymmetric poroelastic model of human lumbar L4–L5 motion segment was developed. The model was validated by comparing the height loss and intradiscal pressure of the L4–L5 intervertebral disc with in vitro cadaveric studies. The effect of permeability, void ratio, elastic modulus, and Poisson's ratio on disc height and pore pressure was investigated for the following three loading conditions: (1) 1334 N creep loading, (2) peak-to-peak, 1000-to-1600 N, 1 Hz cyclic loading, and (3) same loading magnitude, but at 5 Hz loading frequency. The disc height loss and pore pressure of the three loading conditions were analyzed. The predictions of the disc height loss and intradiscal pressure of the current FE model are well comparable with the results of in vitro cadaveric studies. After model validation, the parametric study of disc poroelastic properties on the disc mechanical responses shows that the increase of permeability and void ratio increases the disc height loss and decreases the pore pressure, and these effects are sensitive to external loading frequency. Higher elastic modulus reduces the disc deformation and the pore pressure, but this reduction is not sensitive to the loading frequency. The effect of Poisson's ratio on disc height loss and pore pressure is negligible. In conclusion, the hydraulic permeability describes the fluid flow capability within tissue matrix which has a higher sensitivity on the saturation time for disc deformation and pore pressure. Void ratio directly affects the amount of mobile water within disc and changes time-dependent response of disc. Increase in loading frequency reduces time for fluid inflow and outflow, which fades out the role of permeability and void ratio. Values of elastic modulus and Poisson's ratio, which demonstrates stiffness and bulging capacity, respectively, do not affect the overall dynamic response of disc.

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Influence of the loading frequency on the wear rate of a polyethylene-on-metal lumbar intervertebral disc replacement

European Spine Journal ◽

10.1007/s00586-010-1582-8 ◽

2010 ◽

Vol 21 (S5) ◽

pp. 709-716 ◽

Cited By ~ 9

Author(s):

Annette Kettler ◽

Michael Bushelow ◽

Hans-Joachim Wilke

Keyword(s):

Wear Rate ◽

Intervertebral Disc ◽

Disc Replacement ◽

Loading Frequency ◽

Lumbar Intervertebral Disc

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Effects of Compression on Glucose Consumption in Intervertebral Disc

ASME 2008 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2008-192812 ◽

2008 ◽

Author(s):

Chun-Yuh Huang ◽

Wei Yong Gu

Keyword(s):

Intervertebral Disc ◽

Theoretical Study ◽

Mixture Theory ◽

Glucose Consumption ◽

Nutrient Level ◽

Metabolic Rates ◽

Unconfined Compression ◽

Theoretical Formulation ◽

Tissue Integrity ◽

Cartilaginous Tissues

Nutrition supply is a concern for the health of avascular cartilaginous tissues such as intervertebral disc (IVD). Maintaining tissue integrity relies on cellular biosynthesis of extracellular matrix, which is an energy demanding process [1]. In the IVD, energy is mainly generated through glycolysis (i.e., glucose consumption). Metabolism of nutrients (e.g., oxygen and glucose) within the IVD depends on local concentrations of nutrients, and coupling effects between nutrient level and metabolic rate [2,3]. Our previous theoretical study had developed a new theoretical formulation by incorporating the metabolic rates of solutes into the mechano-electrochemical mixture theory [4,5]. By using this new theoretical model, the distribution of oxygen and lactate can be predicted within the IVD under static and dynamics compressions [4]. However, the effect of compression on glucose consumption in the IVD has not been studied. The objective of this study was to examine the effects of compression on glucose consumption in the IVD under static and dynamic unconfined compression numerically.

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Analysis of Solute Transport in Cartilaginous Tissue Under Dynamic Unconfined Compression

Advances in Bioengineering ◽

10.1115/imece2003-43066 ◽

2003 ◽

Author(s):

Hai Yao ◽

Wei Yong Gu

Keyword(s):

Dynamic Compression ◽

Electrical Potential ◽

Loading Frequency ◽

Mechanical Forces ◽

The Finite Element Method ◽

Unconfined Compression ◽

Cartilage Sample ◽

Cartilaginous Tissues ◽

Transduction Mechanisms ◽

Theoretical Analyses

Transport of fluid and solutes through the extracellular matrix plays a key role in the nutrition and growth of cartilaginous tissues that lack blood supply. It has been found that the mechanical loading can alter the transport rates of solutes within cartilage [Bonassar, 2000; O’Hara, 1990; Quinn, 2002]. Dynamic compression may enhance the transport of large solutes (e.g., growth factors) within the tissue. Many theoretical analyses have been reported in literature on the transport of fluid and solutes, as well as physical signals (stress, strain, pressure, concentrations, and electrical potential) in cartilage under unconfined compression [Armstrong, 1984; Levenston, 1999; Mow, 2002]. However, little is known as to how the tissue fixed charge density (FCD) affects the transport of fluid and neutral solutes (e.g., glucose and IGF-1) in cartilage sample in dynamic compression. In this study, we numerically analyzed the transport of fluid and solutes, as well as the mechano-electrochemical signals within the cartilage sample in dynamic unconfined compression, using the finite element method (FEM). The objective of this study was to investigate the effects of FCD, loading frequency, and loading platens (permeable vs. impermeable) on the transport of fluid, ions, and neutral solutes within cartilage. This study is essential for the understanding of tissue nutrition and signal transduction mechanisms in cartilage subjected to mechanical forces.

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Distribution of Oxygen, Glucose and Lactate in Degenerated Intervertebral Disc

ASME 2009 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2009-206557 ◽

2009 ◽

Author(s):

Chun-Yuh Huang ◽

Wei Yong Gu

Keyword(s):

Elastic Modulus ◽

Intervertebral Disc ◽

Mechanical Loading ◽

Material Properties ◽

Mixture Theory ◽

Unconfined Compression ◽

Fixed Charge Density ◽

Tissue Degeneration ◽

Solute Diffusivity ◽

Diffusion And Convection

Poor nutritional supply has been a major concern for the health of intervertebral disc (IVD) since the IVD is the largest avascular tissue in the human body. The transport of vital nutrients to cells relies on diffusion and convection through the extracellular matrix (ECM) in the IVD. Transport and metabolism of nutrients (e.g., oxygen and glucose) within the IVD depend on many factors, including the material properties of ECM (e.g., permeability, elastic modulus, and solute diffusivity), cellular metabolic rates, nutritional supply at the edge of the IVD, and mechanical loading [1–6]. Tissue degeneration alters the material properties of the IVD, such as an increase in elastic modulus and a decrease in water content, fixed charge density, permeability and solute diffusivity [6]. However, the effect of tissue degeneration on transport and metabolism of nutrients in the IVD under mechanical loading has not been elucidated. The objective of this study was to numerically investigate the distribution of glucose, oxygen and lactate in the degenerated IVD under static unconfined compression using the mechano-electrochemical mixture theory [7].

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Effects of Compression on Distributions of Oxygen and Lactate in Intervertebral Disc

ASME 2007 Summer Bioengineering Conference ◽

10.1115/sbc2007-176025 ◽

2007 ◽

Author(s):

Chun-Yuh Huang ◽

Wei Yong Gu

Keyword(s):

Intervertebral Disc ◽

Theoretical Study ◽

Dynamic Compression ◽

Nutrient Supply ◽

Theoretical Studies ◽

Cartilaginous Tissue ◽

Unconfined Compression ◽

Solute Fluxes ◽

Triphasic Theory ◽

New Formulation

Since the intervertebral disc (IVD) is the largest avascular cartilaginous structure in the human body, poor nutrient supply has been suggested as a potential mechanism for disc degeneration. The previous theoretical studies have shown that the distributions of nutrients and metabolites (e.g., oxygen, glucose, and lactate) within the IVD depended on tissue diffusivities, nutrient supply, cellular metabolic rates, and coupling effects between nutrient and metabolite [1,2]. Our recent theoretical study suggested that dynamic compression can promote transport of neutral solute in the anisotropic cartilaginous tissue by enhancing both diffusive and convective solute fluxes [3]. However, the effect of compression on distributions of nutrients and metabolites in the IVD has not been studied. The objective of this study was to examine the effects of compression on distributions of oxygen and lactate in the IVD under static and dynamic unconfined compression using a new formulation of the triphasic theory.

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Disc Nucleus Cellular Response to Dynamic Pressures at Critical Frequencies: A Pig Model

Advances in Bioengineering ◽

10.1115/imece2003-43092 ◽

2003 ◽

Author(s):

W. David Merryman ◽

Kristen Loveless ◽

Mehran Kasra

Keyword(s):

Intervertebral Disc ◽

Cellular Response ◽

Culture Media ◽

Synthesis Rate ◽

Control Group ◽

Loading Frequency ◽

Nucleus Pulposus Cells ◽

Destructive Effect ◽

Wide Range

Disc degeneration is a multifactor phenomenon. It has been found that intervertebral disc (IVD) cells respond to such factors as pH, osmotic pressure, genetic factors, and mechanical loading (Guilak, 1999). During daily activities the human intervertebral disc is exposed to oscillatory hydrostatic loads that produce pressures >2MPa in vivo (Nachemson, 1964 and 1979). It is known that dynamic loads with critical frequencies close to that of the in vivo human spine resonant frequency (4–5 Hz) have a destructive effect on disc tissue properties (Pope, 1993). Whether this destructive effect is purely mechanical, due to loading magnification, or biological, affecting cell metabolism, is unknown. Previous work (Merryman, 2002) showed that there was no significant effect upon monolayer IVD cells loaded at 15Hz, while lower frequencies (1 and 8Hz) altered collagen synthesis compared to control. To address this issue, we developed a mechanically active culture system capable of delivering a wide range of loading frequencies and amplitudes of hydrostatic pressure to cultures of disc cells. Nucleus pulposus cells of pig discs were isolated and suspended in alginate beads. Alginate cultures were divided into 6 groups; five groups were exposed to cyclic pressures of frequencies 1, 3, 5, 8, and 10Hz with the same amplitude of 1MPa, and group 6 was the control group (no loading). Cultures of different groups were loaded for 3 days (30 minutes daily) in a hydraulic chamber filled with culture media. The effect of loading frequency on collagen metabolism among different groups was compared by measuring incorporated [3H]-proline into collagen for medium and total extracts. The results indicated a poor synthesis rate and more degradation near the 5Hz frequency.

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