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Initiation and progression of mechanical damage in the intervertebral disc under cyclic loading using continuum damage mechanics methodology: A finite element study.

ABSTRACT: It is difficult to study the breakdown of disc tissue over several years of exposure to bending and lifting by experimental methods. There is also no finite element model that elucidates the failure mechanism due to repetitive loading of the lumbar motion segment. The aim of this study was to refine an already validated poro-elastic finite element model of lumbar motion segment to investigate the initiation and progression of mechanical damage in the disc under simple and complex cyclic loading conditions. Continuum damage mechanics methodology was incorporated into the finite element model to track the damage accumulation in the annulus in response to the repetitive loading. The analyses showed that the damage initiated at the posterior inner annulus adjacent to the endplates and propagated outwards towards its periphery under all loading conditions simulated. The damage accumulated preferentially in the posterior region of the annulus. The analyses also showed that the disc failure is unlikely to happen with repetitive bending in the absence of compressive load. Compressive cyclic loading with low peak load magnitude also did not create the failure of the disc. The finite element model results were consistent with the experimental and clinical observations in terms of the region of failure, magnitude of applied loads and the number of load cycles survived.

SUBMITTER: Qasim M

PROVIDER: S-EPMC3787695 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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Initiation and progression of mechanical damage in the intervertebral disc under cyclic loading using continuum damage mechanics methodology: A finite element study.

Qasim Muhammad M Natarajan Raghu N RN An Howard S HS Andersson Gunnar B J GB

Journal of biomechanics 20120608 11

It is difficult to study the breakdown of disc tissue over several years of exposure to bending and lifting by experimental methods. There is also no finite element model that elucidates the failure mechanism due to repetitive loading of the lumbar motion segment. The aim of this study was to refine an already validated poro-elastic finite element model of lumbar motion segment to investigate the initiation and progression of mechanical damage in the disc under simple and complex cyclic loading ...[more]

PMID: 22682891

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Project description:Human intervertebral disc tissue was obtained from patients (average age 51 yrs) undergoing surgery for lumbar interbody fusion (n=3) or lumbar disc herniation (n=1). Cells were isolated by sequential pronase-collagenase digestion [3]. Cells were passaged twice in monolayer and suspended at a density of 2 x 106 cells/ml in 1.2% alginate (low viscosity, Sigma Chemical, St Louis, MO) dissolved in 150 mM NaCl. Alginate beads were formed by dropwise addition of the alginate from a 22 gauge needle into 102 mM CaCl2, followed by 10 minutes of curing, as described previously [13, 27]. Cell-gel beads were incubated in cell culture media consisting of Ham’s F-12 medium (Gibco BRL, Grand Island, NY), supplemented with 10% FBS (HyClone, Logan, UT), 25 μg/ml ascorbic acid (Sigma, St. Louis, MO), 100 U/ml penicillin, 100 μg/ml streptomycin, and 1 μg/ml Fungizone at 5% CO2 and 37° C. After 24 h, the cell culture medium was removed via pipette and exchanged for one of three osmotically active solutions, representing iso-osmotic, hyper-osmotic and hypo-osmotic media [12, 23, 34]. The iso-osmotic solution consisted of a defined cell culture medium (Ham’s F-12 with supplements as described above; 293 mOsm/kg H2O). The hypo-osmotic solution consisted of the same cell culture media diluted with de-ionized water to a final osmolarity of 250 mOsm/kg H2O. The hyper-osmotic solution consisted of the same cell culture media supplemented with sucrose to a final osmolarity of 450 mOsm/kg H20. The osmolarity of all solution formulations was determined using a freezing-point osmometer (Advanced Laboratory Wide Range 3W2, Advanced Instrument, Needham Heights, MA) as described previously [12]. Cell-alginate beads were cultured for a 4 hour period under one of these conditions, after which the cells were released from alginate in a dissolving buffer (55 mM Na-citrate and 150 mM NaCl), lysed and stored at –80°C. Intervertebral disc (IVD) cells experience a broad range of physical stimuli under physiologic conditions, including alterations in their osmotic environment. In this study, the gene expression profile of human IVD cells was quantified with gene array technology following exposure to varying osmolarity in order to capture the biological responses for a broad set of targets. A total of 42 genes were identified in IVD cells as significantly changed following culture under hyper-osmotic conditions, while a total of 18 genes were identified as significantly changed under hypo-osmotic conditions. Gene expression patterns were verified using RT-PCR. Genes identified in this study include those related to cytoskeleton remodeling and stabilization (ephrin-B2, sarcoglycan beta, IQGAP1), as well as membrane transport (ion transporter SLC21A12, osmolyte tranporter SLC5A3, monocarboxylic acid SLC16A6, and amino acid transporter SLC7A8). An unexpected finding was the differential regulation of the gene for the neurotrophin brain-derived neurotrophic factor by hyper-osmotic stimuli that may be indicative of a physiological response of IVD cells to physical stimuli important in regulating discogenic pain. Keywords = intervertebral disc Keywords = osmotic stimuli Keywords: other

Dataset Information

Initiation and progression of mechanical damage in the intervertebral disc under cyclic loading using continuum damage mechanics methodology: A finite element study.

Publications

Initiation and progression of mechanical damage in the intervertebral disc under cyclic loading using continuum damage mechanics methodology: A finite element study.

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