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Journal ArticleDOI

Single lamellar mechanics of the human lumbar anulus fibrosus

TL;DR: The single anulus lamella may be seen as the elementary structural unit of the anulus fibrosus, and exhibits marked anisotropy and distinct regional variation of tensile properties and fiber angles.
Abstract: The mechanical behavior of the entire anulus fibrosus is determined essentially by the tensile properties of its lamellae, their fiber orientations, and the regional variation of these quantities. Corresponding data are rare in the literature. The paper deals with an in vitro study of single lamellar anulus lamellae and aims to determine (i) their tensile response and regional variation, and (ii) the orientation of lamellar collagen fibers and their regional variation. Fresh human body-disc-body units (L1–L2, n=11) from cadavers were cut midsagittally producing two hemidisc units. One hemidisc was used for the preparation of single lamellar anulus specimens for tensile testing, while the other one was used for the investigation of the lamellar fiber orientation. Single lamellar anulus specimens with adjacent bone fragments were isolated from four anatomical regions: superficial and deep lamellae (3.9±0.21 mm, mean ± SD, apart from the outer boundary surface of the anulus fibrosus) at ventro-lateral and dorsal positions. The specimens underwent cyclic uniaxial tensile tests at three different strain rates in 0.15 mol/l NaCl solution at 37°C, whereby the lamellar fiber direction was aligned with the load axis. For the characterization of the tensile behavior three moduli were calculated: Elow (0–0.1 MPa), Emedium (0.1–0.5 MPa) and Ehigh (0.5–1 MPa). Additionally, specimens were tested with the load axis transverse to the fiber direction. From the second hemidisc fiber angles with respect to the horizontal plane were determined photogrammetrically from images taken at six circumferential positions from ventral to dorsal and at three depth levels. Tensile moduli along the fiber direction were in the range of 28–78 MPa (regional mean values). Superficial lamellae have larger Emedium (p=0.017) and Ehigh (p=0.012) than internal lamellae, and the mean value of superficial lamellae is about three times higher than that of deep lamellae. Tensile moduli of ventro-lateral lamellae do not differ significantly from the tensile moduli of dorsal lamellae, and Elow is generally indifferent with respect to the anatomical region. Tensile moduli transverse to the fiber direction were about two orders of magnitude smaller (0.22±0.2 MPa, mean ± SD, n=5). Tensile properties are not correlated significantly with donor age. Only small viscoelastic effects were observed. The regional variation of lamellar fiber angle ϕ is described appropriately by a regression line |ϕ|=23.2+0.130×α (r2=0.55, p<0.001), where α is the polar angle associated with the circumferential position. The single anulus lamella may be seen as the elementary structural unit of the anulus fibrosus, and exhibits marked anisotropy and distinct regional variation of tensile properties and fiber angles. These features must be considered for appropriate physical and numerical modeling of the anulus fibrosus.
Citations
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Journal ArticleDOI
TL;DR: It is indicated that cell infiltration can be expedited in dense fibrous assemblies with the removal of sacrificial fibers, and this strategy may enhance in vitro and in vivo formation and maturation of functional constructs for fibrous tissue engineering.

613 citations

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TL;DR: It is argued that mechanics and biology are interconnected and amplify each other and the proposed disease model explains the comparable efficacy of very different animal models of disc degeneration, but also helps to consider the consequences of therapeutic interventions, either at the cellular, material or mechanical level.

528 citations

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TL;DR: Three-dimensional, nonlinear finite element model of the L3/L4 functional unit was used to study the influence of disc degeneration on motion segment mechanics and found that a mildly degenerated disc increases intersegmental rotation for all loading cases.

345 citations


Cites background from "Single lamellar mechanics of the hu..."

  • ...It was assumed that disc degeneration has no effect on the material properties of the annulus fibrosus (Holzapfel et al., 2005)....

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Journal ArticleDOI
TL;DR: A method was developed for calibrating the two-composite structure of the annulus fibrosus, the ground substance and collagen fibers to fulfil the required range of motion obtained from in vitro results within an accuracy of 99%.

320 citations

Journal ArticleDOI
TL;DR: The role of biomechanics on disc degeneration and regenerative therapies is evaluated with a focus on what biomechanical properties need to be repaired and how to evaluate and accomplish such repairs using biomaterials.

250 citations


Additional excerpts

  • ...[155] Holzapfel GA, Schulze-Bauer CA, Feigl G, Regitnig P....

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  • ...22 MPa in the transverse direction [155,156]....

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References
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Journal ArticleDOI
01 May 1990-Spine
TL;DR: A five-category grading scheme for assessing the gross morphology of midsagittal sections of the human lumbar intervertebral disc was developed and the ability of three observers to categorize a series of 68 discs with a wide spectrum of morphologies established the comprehensiveness of the classification.
Abstract: A five-category grading scheme for assessing the gross morphology of midsagittal sections of the human lumbar intervertebral disc was developed. The ability of three observers to categorize a series of 68 discs with a wide spectrum of morphologies established the comprehensiveness of the classificat

850 citations


"Single lamellar mechanics of the hu..." refers methods in this paper

  • ...Disc cross-sections were assessed with respect to the Thompson et al. (1990) scheme, and tensile tests were performed solely with non-degenerated or minimally degenerated discs, i.e., six discs were used with grade I and five with grade II....

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Journal ArticleDOI
01 May 1990-Spine
TL;DR: The structure of the lumbar disc anulus fibrosus was investigated using a layer-by-layer peeling technique and microscopic examination of various cut surfaces to identify mechanisms of layer interruption at local laminate irregularities.
Abstract: The structure of the lumbar disc anulus fibrosus was investigated using a layer-by-layer peeling technique and microscopic examination of various cut surfaces. Anulus specimens from spines of two different age groups and from two levels, L2–3 and L4–5, were examined. The vertebra-disc-vertebra units

546 citations


"Single lamellar mechanics of the hu..." refers background or result in this paper

  • ...…University Graz, Harrachgasse 21, Graz, 8010, Austria P. Regitnig Institute of Pathology, Medical University Graz, Auenbruggerplatz 25, Graz, 8036, Austria transverse plane of the spine, whereby this angle varies in circumferential and radial directions; see, for example, Marchand and Ahmed (1990)....

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  • ...These results are consistent with previous findings by Marchand and Ahmed (1990), who measured the lamellar fiber angles at the ventral and dorsal midsagittal position for the lumbar levels L2–L3 and L4–L5....

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  • ...In contrast to the latter result, previous studies (Cassidy et al. 1989; Hsu and Setton 1999; Marchand and Ahmed 1990) report that the lamellar thickness is larger at the internal regions than at the external regions of the anulus fibrosus....

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  • ...One reason may be the frequent occurrence of laminate irregularities particularly in these regions (Marchand and Ahmed 1990)....

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  • ...…fiber angle increases from 28 at the edge of the disc to 45 beside the nucleus pulposus referred to as the transverse plane of the spine, while the intra-lamellar variation of the fiber angle ranges from about 20 at the ventral position to about 70 at the dorsal position (Marchand and Ahmed 1990)....

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Journal ArticleDOI
01 Feb 1988-Spine
TL;DR: The relationship between change In hydratlon and swelling pressure was found to depend on the composition of the disc rather than on age or degree of degeneration, and could be predicted satisfactorily for a disc of known collagen and proteoglycan content.
Abstract: The fluid content of the intervertebral disc is important in determining its mechanical response and also its transport and biologic properties. Fluid content depends on the proteoglycan content of the tissue and on the relationship of the external load to the disc's swelling pressure. The influence of proteoglycan content and external load on the hydration of nuclei from 32 human lumbar discs was measured. Swelling pressure of the same specimens was measured by equilibrium dialysis. The influence of age (14-91 years) and spinal level was noted. Proteoglycan content of the discs fell with age, and for all spines tested, proteoglycan content was lowest in the L5-S1 disc; no systematic change in collagen content was found. The hydration of the discs, as received, also fell with increase in age; in each complete lumbar spine tested, the L1-L2 and the L5-S1 discs had the lowest hydration at postmortem examination. As the stress applied to the discs was increased, hydration decreased. Although a stress of 0.10-0.23 MPa maintained the disc slices at their postmortem hydration, under a stress of about 0.6-0.8 MPa, most discs lost 40-60% of their initial fluid. The relationship between change in hydration and swelling pressure was found to depend on the composition of the disc rather than on age or degree of degeneration; the relationship between equilibrium hydration and swelling pressure could be predicted satisfactorily for a disc of known collagen and proteoglycan content.

449 citations


"Single lamellar mechanics of the hu..." refers background in this paper

  • ...…because it is known that aging is associated with significant chemical changes of the anulus fibrosus, such as a reduction of the water content (Hickey et al. 1986; Isherwood et al. 1986; Jenkins et al. 1985; Urban and McMullin 1988) and the amount of proteoglycans (Urban and McMullin 1988)....

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  • ...Moreover, this result is particularly surprising, because it is known that aging is associated with significant chemical changes of the anulus fibrosus, such as a reduction of the water content (Hickey et al. 1986; Isherwood et al. 1986; Jenkins et al. 1985; Urban and McMullin 1988) and the amount of proteoglycans (Urban and McMullin 1988)....

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  • ...1985; Urban and McMullin 1988) and the amount of proteoglycans (Urban and McMullin 1988)....

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Journal ArticleDOI
TL;DR: A hierarchical model of the intervertebral disc has been developed that incorporates morphological gradients that include lamellae in the lateral and posterior aspects of the disc and collagen fibers in the anterior annulus fibrosus.
Abstract: Optical microscope techniques are used to characterize the hierarchical structure of the collagenous components of the human intervertebral disc. In the anterior annulus fibrosus, the thickness of lamellae increases abruptly 2 mm inward from the edge of the disc, dividing the annulus into peripheral and transitional regions. Lamellae in the lateral and posterior aspects of the disc have a broad distribution of lamellar thicknesses throughout the annulus. In alternating lamellae, fibers are inclined with respect to the vertical axis of the spine in a layup structure. From the edge of the disc inward to the nucleus, this interlamellar angle decreases from + 62 to + 45 degrees. Within lamellae, the collagen fibers exhibit a planar crimped morphology. The plane of the waveform is inclined with respect to the vertical axis by the interlamellar angle. From the edge of the disc inward, the crimp angle increases from 20 to 45 degrees and the crimp period decreases from 26 to 20 um. A hierarchical model of the int...

447 citations


"Single lamellar mechanics of the hu..." refers background or result in this paper

  • ...There might be a more significant relation between fiber angles and radial position for deeper lamellae as reported by other studies (Cassidy et al. 1989; Marchand and Ahmed 1990)....

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  • ...In contrast to the latter result, previous studies (Cassidy et al. 1989; Hsu and Setton 1999; Marchand and Ahmed 1990) report that the lamellar thickness is larger at the internal regions than at the external regions of the anulus fibrosus....

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  • ...Cassidy et al. (1989) document that the lamellar fiber angle increases from 28 at the edge of the disc to 45 beside the nucleus pulposus referred to as the transverse plane of the spine, while the intra-lamellar variation of the fiber angle ranges from about 20 at the ventral position to about 70…...

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  • ...The most cited and seminal detailed works concerned with the anatomical structure of the anulus fibrosus are the studies by Marchand and Ahmed (1990) and Cassidy et al. (1989), which are based on light microscopy techniques....

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Journal ArticleDOI
TL;DR: In this article, the tensile properties of the human Lumbar Annulus Fibrosus were investigated and the human lumbar annulus fibrosus was found to have a tensile tensile property.
Abstract: (1967). Tensile Properties of the Human Lumbar Annulus Fibrosus. Acta Orthopaedica Scandinavica: Vol. 38, No. sup100, pp. 1-91.

407 citations


"Single lamellar mechanics of the hu..." refers background or result in this paper

  • ...Most of these studies utilize multi-lamellar specimens with circumferential (Acaroglu et al. 1995; Ebara et al. 1996; Elliott and Setton 2001; Galante 1967; Wu and Yao 1976), axial (Elliott and Setton 2001), and radial orientations (Elliott and Setton 2001; Fujita et al. 1997)....

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  • ...Most of these studies utilize multi-lamellar specimens with circumferential (Acaroglu et al. 1995; Ebara et al. 1996; Elliott and Setton 2001; Galante 1967; Wu and Yao 1976), axial (Elliott and Setton 2001), and radial orientations (Elliott and Setton 2001; Fujita et al....

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  • ...These results agree with previous findings by Ebara et al. (1996) and Galante (1967), who documented only a weak correlation between age and tensile behavior....

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