Mechanisms for mechanical damage in the intervertebral disc annulus fibrosus

Abstract

Intervertebral disc degeneration results in disorganization of the laminate structure of the annulus that may arise from mechanical microfailure. Failure mechanisms in the annulus were investigated using composite lamination theory and other analyses to calculate stresses in annulus layers, interlaminar shear stress, and the region of stress concentration around a fiber break. Scanning electron microscopy (SEM) was used to evaluate failure patterns in the annulus and evaluate novel structural features of the disc tissue. Stress concentrations in the annulus due to an isolated fiber break were localized to approximately 5 microm away from the break, and only considered a likely cause of annulus fibrosus failure (i.e., radial tears in the annulus) under extreme loading conditions or when collagen damage occurs over a relatively large region. Interlaminar shear stresses were calculated to be relatively large, to increase with layer thickness (as reported with degeneration), and were considered to be associated with propagation of circumferential tears in the annulus. SEM analysis of intervertebral disc annulus fibrosus tissue demonstrated a clear laminate structure, delamination, matrix cracking, and fiber failure. Novel structural features noted with SEM also included the presence of small tubules that appear to run along the length of collagen fibers in the annulus and a distinct collagenous structure representative of a pericellular matrix in the nucleus region.

Nucleus pulposus glycosaminoglycan content is correlated with axial mechanics in rat lumbar motion segments

“…As nucleus glycosaminoglycan contents are progressively decreased, the disc may be exposed to increasingly larger deformations and strains at normal physiologic loads, potentially increasing the risk of structural damage such as annulus delamination and microtrauma. 3,47 Finite element models are in agreement with this scenario, showing that discs become hypermobile with a loss of pressure, and demonstrating that the annulus fibrosus experiences higher stresses and strains. [48][49][50] Not only do the increased stresses and strains within the disc pose a direct mechanical damage threat, but this altered mechanical behavior likely alters cellular function.…”

Engineering on the Straight and Narrow: The Mechanics of Nanofibrous Assemblies for Fiber-Reinforced Tissue Regeneration

“…Middle image from Ref. 138 Scale bar ¼ 200 mm, used with permission from Elsevier. Right image from Ref.…”

The elastic fibre network of the human lumbar anulus fibrosus: architecture, mechanical function and potential role in the progression of intervertebral disc degeneration

“…The physiological relevance of cross-connecting elastic fibres within and between lamellae is evident when considered in the context of the most common manifestations of matrix damage which have been observed following both fatigue loading and over-pressurisation [22,23,53]. For example, in the absence of the elastic fibres which maintain adhesion between lamellae, the shear strains which occur as a result of relative reorientation between those lamellae in bending and torsion may increase the propensity for delaminations and circumferential tears to form.…”