Annulus fibrosus functional extrafibrillar and fibrous mechanical behaviour: experimental and computational characterisation

Abstract

The development of current surgical treatments for intervertebral disc damage could benefit from virtual environment accounting for population variations. For such models to be reliable, a relevant description of the mechanical properties of the different tissues and their role in the functional mechanics of the disc is of major importance. The aims of this work were first to assess the physiological hoop strain in the annulus fibrosus in fresh conditions (n = 5) in order to extract a functional behaviour of the extrafibrillar matrix; then to reverse-engineer the annulus fibrosus fibrillar behaviour (n = 6). This was achieved by performing both direct and global controlled calibration of material parameters, accounting for the whole process of experimental design and in silico model methodology. Direct-controlled models are specimen-specific models representing controlled experimental conditions that can be replicated and directly comparing measurements. Validation was performed on another six specimens and a sensitivity study was performed. Hoop strains were measured as 17 ± 3% after 10 min relaxation and 21 ± 4% after 20–25 min relaxation, with no significant difference between the two measurements. The extrafibrillar matrix functional moduli were measured as 1.5 ± 0.7 MPa. Fibre-related material parameters showed large variability, with a variance above 0.28. Direct-controlled calibration and validation provides confidence that the model development methodology can capture the measurable variation within the population of tested specimens.

Biomechanical modelling of the facet joints: a review of methods and validation processes in finite element analysis

“…This review of 110 papers from the last 30+ years has shown that there is, to date, no finite element model of the human functional spinal unit (two or more levels) which provides direct validation of the facet joint behaviour. Direct validation is here defined as the direct comparison between a computational result and an experimental result of the same specimen, when the computational model and the experiment match as closely as possible (Jones and Wilcox 2008;Mengoni et al 2017). All quantitative validation processes for the facet joints in the reviewed studies use comparison with the existing literature data, either computational data or experimental data, all assuming healthy facet joint properties.…”

Multi-laminate annulus fibrosus repair scaffold with an interlamellar matrix enhances impact resistance, prevents herniation and assists in restoring spinal kinematics

“…This is likely the result of two phenomena; 1) a lack of tissue integration between the AF tissue plug and the adjacent AF, and 2) the inability to restore circumferential residual pre-strains found within the intact AF. (Mengoni et al, 2017;Michalek et al, 2012) The former could be addressed by using a composite repair strategy using a mimetic scaffold to plug the defect pathway that is adhered to adjacent AF tissue using durable adhesive hydrogels prior to securing the implants within the IVD using an AFRP.…”

Multi-laminate Annulus Fibrosus Repair Scaffold with an Interlamellar Matrix Enhances Impact Resistance, Prevents Herniation and Assists in Restoring Spinal Kinematics

“…Long et al, 2016) Thus, the recovery of mechanical torsional properties may also be dependent on the restoration of circumferential residual stresses and prestrains found within the AF. (Mengoni et al, 2017;Michalek et al, 2012) Accordingly, future investigations of AF repair biomaterials should take into consideration the restoration of native residual stresses and pre-strains to further assist in restoring torsional kinematic parameters.…”