A Computational Model to Describe the Regional Interlamellar Shear of the Annulus Fibrosus

Labus, Kevin M.; Han, Sang Kuy; Hsieh, Adam H.; Puttlitz, Christian M.

doi:10.1115/1.4027061

Cited by 15 publications

(12 citation statements)

References 39 publications

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“…Furthermore, changes in both ITL and lamellar strain decreased with greater applied load. These observed differences are qualitatively consistent with trends we found in a previous study, 33 in which a nonlinear constitutive model parameters fit to surface strain measurements yielded a interlamellar shear modulus that was roughly half the lamellar shear modulus, both of which increased with higher applied strain (strain stiffening). However, in contrast to previous studies using lower applied shear strains, 47 our averaged ITL and lamellar shear strain was not equal to the applied strain; this could be an indication of matrix damage, likely in the ITL compartment.…”

Section: Discussionsupporting

confidence: 91%

“…Previous studies have suggested that the ITL compartment contributes little to AF mechanics in radial tension. 23,45,46 Instead, it has been postulated that the ITL may play a greater role in maintaining annular integrity during shear loading, 32,33 as supported by the absence of sliding between lamellae due to fibrous interlamellar connectivity. 47 At high deformations, however, the ability for interlamellar sliding to occur suggests complexity in the load sharing between the ITL and lamellar matrix.…”

Section: Discussionmentioning

confidence: 99%

“…Recently, using a combinatorial approach of tissue testing and computational modeling, we investigated circumferential shear loading of ovine AF tissue and found that the shear modulus is much higher within lamellae than between lamellae. 33 At the microstructural level, collagen fiber sliding and shear deformation within and across AF lamellae have been observed in bovine IVDs during motion segment bending. 34 The morphology of interlamellar matrix under microtensile loading and intradiscal pressurization also suggest vulnerability to damage.…”

Section: Introductionmentioning

confidence: 98%

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Optical Coherence Tomographic Elastography Reveals Mesoscale Shear Strain Inhomogeneities in the Annulus Fibrosus

Han

Chen

Labus

et al. 2016

Spine

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STRUCTURED ABSTRACT Study Design Basic science study using in vitro tissue testing and imaging to characterize local strains in annulus fibrosus (AF) tissue. Objective To characterize mesoscale strain inhomogeneities between lamellar and inter-/translamellar (ITL) matrix compartments during tissue shear loading. Summary of Background Data The intervertebral disc (IVD) is characterized by significant heterogeneities in tissue structure and plays a critical role in load distribution and force transmission in the spine. In particular, the AF possesses a lamellar architecture interdigitated by a complex network of extracellular matrix components that form a distinct ITL compartment. Currently, there is not a firm understanding of how the lamellar and ITL matrix coordinately support tissue loading. Methods AF tissue samples were prepared from frozen porcine lumbar spines and mounted onto custom fixtures of a materials testing system that incorporates optical coherence tomography (OCT) imaging in order to perform tissue elastography. Tissues were subjected to 20 and 40% nominal shear strain, and OCT images were captured and segmented to identify regions of interest corresponding to lamellar and ITL compartments. Images were analyzed using an optical flow algorithm to quantify local shear strains within each compartment. Results Using histology and OCT, we first verified our ability to visualize and discriminate the ITL matrix from the lamellar matrix in porcine AF tissues. Local AF strains in the ITL compartment (22.0 ± 13.8, 31.1 ± 16.9 at 20% and 40% applied shear, respectively) were significantly higher than corresponding strains in the surrounding lamellar compartment (12.1 ± 5.6, 15.3 ± 5.2) for all tissue samples (p<0.05). Conclusions Results from this study demonstrate that the lamellar and ITL compartments of the AF distribute strain unevenly during tissue loading. Specifically, shear strain is significantly higher in the ITL matrix, suggesting that these regions may be more susceptible to tissue damage and more mechanobiologically active.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Optical Coherence Tomographic Elastography Reveals Mesoscale Shear Strain Inhomogeneities in the Annulus Fibrosus

Han

Chen

Labus

et al. 2016

Spine

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“…56 Therefore, extending the existing theoretical framework would be helpful to describe the ILM shearing interaction. [56][57][58] Structural damage to the lamellae, mainly as a consequence of degeneration, might increase ILM shear stress and damage propagation.…”

Section: Inter-lamellar Matrix Micromechanical Propertiesmentioning

confidence: 99%

Structure and mechanical function of the inter‐lamellar matrix of the annulus fibrosus in the disc

Tavakoli

Elliott

Costi

2016

Journal Orthopaedic Research

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The inter-lamellar matrix (ILM) has an average thickness of less than 30 mm and lies between adjacent lamellae in the annulus fibrosus (AF). The microstructure and composition of the ILM have been studied in various anatomic regions of the disc; however, their contribution to AF mechanical properties and structural integrity is unknown. It was suggested that the ILM components, mainly elastic fibers and cross-bridges, play a role in providing mechanical integrity of the AF. Therefore, the manner in which they respond to different loadings and stabilize adjacent lamellae structure will influence AF tear formation and subsequent herniation. This review paper summarizes the composition, microstructure, and potential role of the ILM in the progression of disc herniation, clarifies the micromechanical properties of the ILM, and proposes critical areas for future studies. There are a number of unknown characteristics of the ILM, such as its mechanical role, impact on AF integrity, and ultrastructure of elastic fibers at the ILM-lamella boundary. Determining these characteristics will provide important information for tissue engineering, repair strategies, and the development of more-physiological computational models to study the initiation and propagation of AF tears that lead to herniation and degeneration. Keywords: inter-lamellar matrix; cross-bridges; annulus fibrosus; elastic fibersThe inter-lamellar matrix (ILM) lies between the lamellae of the annulus fibrosus (AF) of the intervertebral disc and has a thickness of less than 30 mm. The ILM is comprised of four main components: Matrix, cross-bridges, elastic fibers, and cells; however, those components are not restricted to the ILM alone (i.e., cross-bridges are present in the ILM space and cross radially through multiple AF layers). 1-5 ILM failure results in delamination (separation of lamellae) and may be one of the initial stages of herniation and degeneration. 6-8 Knowledge of the ILM structure and mechanical function is important to determining the loading conditions under which the AF is at risk of delamination and subsequent disc disruption and herniation. This understanding of the ILM may lead to the development of improved clinical strategies for disc treatment of herniation and painful degenerative disc disorders.AF delamination and tears, and the associated disc degeneration, are directly related to the structural integrity of the ILM. 9-12 Migration of the NP propagates-under certain circumstances-circumferentially, increasing ILM localized stress and risk of delamination in deep (i.e., inner) AF layers. 8 ILM failure and associated delamination alters ovine spine segment mechanics and causes increased lamellar thickness and vertebral bone volume fraction. 7 On the other hand, delamination may also lead to increased tensile loading within the collagenous AF lamellae components. Therefore, the role of the ILM on the AF microstructural integrity 13 and strength is evident, as mechanical properties of multi-lamellae are different from single ...

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“…The ILM shear strength has been found to increase with lamella thickness [22], and deform by up to 10 mm, having a mean (SD) peak shear strength of 0.03 (0.05) MPa during delamination [23]. Significantly different shear stress and strain distributions, with a trend of being greater in the lamella than across the ILM, were found in disc mechanical modelling when inter-lamellar connectivity was considered [24,25]. Also higher strain was reported in the ILM compared to the intra-lamellar region in bovine discs [26].…”

Section: Introductionmentioning

confidence: 97%

New findings confirm the viscoelastic behaviour of the inter-lamellar matrix of the disc annulus fibrosus in radial and circumferential directions of loading

Tavakoli

Costi

2018

Acta Biomaterialia

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While few studies have improved our understanding of composition and organization of elastic fibres in the inter-lamellar matrix (ILM) of the annulus in the disc no studies have measured the direct mechanical failure and viscoelastic properties of the ILM. The findings from this study identified that the stiffness of the ILM was significantly larger at faster strain rates, and energy absorption significantly smaller, compared to slower strain rates. The failure properties of the ILM were not significantly different under tension and shear.

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A Computational Model to Describe the Regional Interlamellar Shear of the Annulus Fibrosus

Cited by 15 publications

References 39 publications

Optical Coherence Tomographic Elastography Reveals Mesoscale Shear Strain Inhomogeneities in the Annulus Fibrosus

Optical Coherence Tomographic Elastography Reveals Mesoscale Shear Strain Inhomogeneities in the Annulus Fibrosus

Structure and mechanical function of the inter‐lamellar matrix of the annulus fibrosus in the disc

New findings confirm the viscoelastic behaviour of the inter-lamellar matrix of the disc annulus fibrosus in radial and circumferential directions of loading

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