Article

The internal mechanical functioning of intervertebral discs and articular cartilage, and its relevance to matrix biology

Department of Anatomy, University of Bristol, Bristol, UK.
Matrix biology: journal of the International Society for Matrix Biology (Impact Factor: 5.07). 08/2009; 28(7):384-9. DOI: 10.1016/j.matbio.2009.06.004
Source: PubMed

ABSTRACT

Degeneration of intervertebral discs and articular cartilage can cause pain and disability. Risk factors include genetic inheritance and age, but mechanical loading also is important. Its influence has been investigated using miniature pressure transducers to measure the distribution of compressive stress (force per unit area) within loaded tissue. The technique quantifies stress concentrations, and detects regions that behave in a fluid-like manner. Intervertebral discs demonstrate a central fluid-like region which normally extends beyond the anatomical nucleus pulposus so that the whole disc functions like a "water bed". With increasing age, the fluid region shrinks and pressure within it falls. Stress concentrations appear in the surrounding anulus fibrosus, with location depending on posture. Stress concentrations become large in degenerated discs, and are intensified by sustained loading or injury. Articular cartilage never exhibits an internal fluid pressure: stress gradients and concentrations normally occur within it, and are intensified by sustained loading. Excessive matrix stresses can cause pain and progressive damage. They also inhibit matrix synthesis and stimulate production of matrix-degrading enzymes. In this way, injury to chondroid tissues can initiate a 'vicious circle' of abnormal matrix stresses, abnormal metabolism, weakened matrix, and further injury, which explains many features of their degeneration.

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    • " Holm et al . , 2004 ) . Nucleus decompression also impairs matrix synthesis by nucleus cells ( Ishihara et al . , 1996 ) , and high stress concentrations in the annulus increase the expression of matrix - degrading enzymes ( Handa et al . , 1997 ) . In this way , endplate damage drives disc degeneration by biological as well as mechanical means ( Adams et al . , 2009 ) . Alternatively , the annulus can be disrupted directly by high or repetitive loading in bending and compres - sion . This type of loading occurs typically during heavy lifting activities ( Dolan et al . , 1994 ) and can cause the nucleus to herniate into ( or through ) the stretched region of annulus ( Adams and Hutton , 1982 , 1985 "
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    ABSTRACT: This review suggests why some discs degenerate rather than age normally. Intervertebral discs are avascular pads of fibrocartilage that allow movement between vertebral bodies. Human discs have a low cell density and a limited ability to adapt to mechanical demands. With increasing age, the matrix becomes yellowed, fibrous, and brittle, but if disc structure remains intact, there is little impairment in function, and minimal ingrowth of blood vessels or nerves. Approximately half of old lumbar discs degenerate in the sense of becoming physically disrupted. The posterior annulus and lower lumbar discs are most affected, presumably because they are most heavily loaded. Age and genetic inheritance can weaken discs to such an extent that they are physically disrupted during everyday activities. Damage to the endplate or annulus typically decompresses the nucleus, concentrates stress within the annulus, and allows ingrowth of nerves and blood vessels. Matrix disruption progresses by mechanical and biological means. The site of initial damage leads to two disc degeneration “phenotypes”: endplate-driven degeneration is common in the upper lumbar and thoracic spine, and annulus-driven degeneration is common at L4-S1. Discogenic back pain can be initiated by tissue disruption, and amplified by inflammation and infection. Healing is possible in the outer annulus only, where cell density is highest. We conclude that some discs degenerate because they are disrupted by excessive mechanical loading. This can occur without trauma if tissues are weakened by age and genetic inheritance. Moderate mechanical loading, in contrast, strengthens all spinal tissues, including discs. Clin. Anat., 2014. © 2014 Wiley Periodicals, Inc.
    Full-text · Article · Apr 2014 · Clinical Anatomy
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    • "The direction of the fibers was angled varying from 40° to 70° to the vertical axis [1]. The intervertebral disc is in contact with the vertebral bodies through CE which is responsible for the exchange of substance through the microporous structure [2]. Anyone off normal of these three parts may cause the disc degeneration. "
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    ABSTRACT: The intervertebral disc degeneration and injury are the most common spinal diseases with tremendous financial and social implications. Regenerative therapies for disc repair are promising treatments. Fiber-reinforced materials (FRMs) are a kind of composites by embedding the fibers into the matrix materials. FRMs can maintain the original properties of the matrix and enhance the mechanical properties. By now, there are still some problems for disc repair such as the unsatisfied static strength and dynamic properties for disc implants. The application of FRMs may resolve these problems to some extent. In this review, six parts such as background of FRMs in tissue repair, the comparison of mechanical properties between natural disc and some typical FRMs, the repair standard and FRMs applications in disc repair, and the possible research directions for FRMs' in the future are stated.
    Full-text · Article · Dec 2013
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    • "Se han desarrollado modelos de elementos finitos poroelásticos para analizar el comportamiento mecánico de discos intervertebrales bajo diferentes estados y tasas de cargas, y se ha encontrado una evidente dependencia de la presión de poros con el desplazamiento [4]. Un caso particular se presenta en los discos intervertebrales de la columna vertebral humana, los cuales son afectados por su grado de degeneración, que está relacionado con la edad del individuo [5]. El disco intervertebral es el componente heterogéneo blando comprendido entre cada par de vértebras, el cual está sometido a grandes fuerzas y le confiere una gran flexibilidad a la columna. "
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    ABSTRACT: con el objeto de conocer la capacidad de predicción de los modelos de elementos finitos de materiales poroelásticos, se validó un modelo simplificado del disco intervertebral de la columna, con valores experimentales obtenidos de modelos construidos con materiales artificiales. Los discos artificiales, construidos con un núcleo de espuma de poliuretano rodeado por un anillo de caucho natural, fueron sometidos a carga de compresión axial y momentos flectores puros. Inicialmente se realizó una caracterización experimental para determinar el módulo de elasticidad, el esfuerzo de fluencia y las curvas no lineales de esfuerzo vs deformación, tanto para el material del anillo como el del núcleo. Adicionalmente se obtuvo la permeabilidad de la espuma de poliuretano con el método de cabeza de presión constante según la norma ASTM D2434. Los resultados obtenidos en la caracterización de los materiales, se usaron como datos de entrada para los modelos de elementos finitos de los discos. En los modelos se consideró la no linealidad de los materiales con una función de energía hiperelástica tipo Ogden, y se incluyó el cambio de permeabilidad con la deformación, con base en una función exponencial. Los resultados de los modelos arrojaron predicciones con una exactitud superior al 87 % respecto al comportamiento experimental. Se observó una influencia importante de la variación de la permeabilidad con la deformación. Además, los modelos de elementos finitos presentaron un comportamiento cualitativamente similar al observado en discos intervertebrales reales, aunque no pudieron predecir las curvas no lineales entre deformación angular y momento obtenidas con disco reales, debido a la ausencia de fibras de refuerzo en los modelos físicos.
    Full-text · Conference Paper · Aug 2013
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