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


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.
    Clinical Anatomy 04/2014; DOI:10.1002/ca.22404 · 1.33 Impact Factor
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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.
    12/2013; 2013:714103. DOI:10.1155/2013/714103
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    • "Indeed, this topic remains controversial as some studies have found a positive association between heavy physical loading, either in occupation or sports, and DD, but negative findings have also been published [38-40]. The harmful effects of sports may be due to trauma, or excessive physical activity causing abnormal stress on the structural components of the disc with failure of the motion segment [41,42]. In the current study, the overall level of physical activity between the ages of 16 to 19 years was not associated with DD with any certainty. "
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    ABSTRACT: The role of environmental factors in lumbar intervertebral disc degeneration (DD) in young adults is largely unknown. Therefore, we investigated whether body mass index (BMI), smoking, and physical activity are associated with lumbar DD among young adults. The Oulu Back Study (OBS) is a subpopulation of the 1986 Northern Finland Birth Cohort (NFBC 1986) and it originally included 2,969 children. The OBS subjects received a postal questionnaire, and those who responded (N = 1,987) were invited to the physical examination. The participants (N = 874) were invited to lumbar MRI study. A total of 558 young adults (325 females and 233 males) underwent MRI that used a 1.5-T scanner at the mean age of 21. Each lumbar intervertebral disc was graded as normal (0), mildly (1), moderately (2), or severely (3) degenerated. We calculated a sum score of the lumbar DD, and analyzed the associations between environmental risk factors (smoking, physical activity and weight-related factors assessed at 16 and 19 years) and DD using ordinal logistic regression, the results being expressed as cumulative odds ratios (COR). All analyses were stratified by gender. Of the 558 subjects, 256 (46%) had no DD, 117 (21%) had sum score of one, 93 (17%) sum score of two, and 92 (17%) sum score of three or higher. In the multivariate ordinal logistic regression model, BMI at 16 years (highest vs. lowest quartile) was associated with DD sum score among males (COR 2.35; 95% CI 1.19-4.65) but not among females (COR 1.29; 95% CI 0.72-2.32). Smoking of at least four pack-years was associated with DD among males, but not among females (COR 2.41; 95% CI 0.99-5.86 and 1.59; 95% 0.67-3.76, respectively). Self-reported physical activity was not associated with DD. High BMI at 16 years was associated with lumbar DD at 21 years among young males but not among females. High pack-years of smoking showed a comparable association in males, while physical activity had no association with DD in either gender. These results suggest that environmental factors are associated with DD among young males.
    BMC Musculoskeletal Disorders 03/2013; 14(1):87. DOI:10.1186/1471-2474-14-87 · 1.72 Impact Factor
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