A biochemical/biophysical 3D FE intervertebral disc model

Abstract

Present research focuses on different strategies to preserve the degenerated disc. To assure long-term success of novel approaches, favorable mechanical conditions in the disc tissue are essential. To evaluate these, a model is required that can determine internal mechanical conditions which cannot be directly measured as a function of assessable biophysical characteristics. Therefore, the objective is to evaluate if constitutive and material laws acquired on isolated samples of nucleus and annulus tissue can be used directly in a wholeorgan 3D FE model to describe intervertebral disc behavior. The 3D osmo-poro-visco-hyper-elastic disc (OVED) model describes disc behavior as a function of annulus and nucleus tissue biochemical composition, organization and specific constituent properties. The description of the 3D collagen network was enhanced to account for smaller fibril structures. Tissue mechanical behavior tests on isolated nucleus and annulus samples were simulated with models incorporating tissue composition to calculate the constituent parameter values. The obtained constitutive laws were incorporated into the whole-organ model. The overall behavior and disc properties of the model were corroborated against in vitro creep experiments of human L4/L5 discs. The OVED model simulated isolated tissue experiments on confined compression and uniaxial tensile test and whole-organ disc behavior. This was possible, provided that secondary fiber structures were accounted for. The fair agreement (radial bulge, axial creep deformation and intradiscal pressure) between model and experiment was obtained using constitutive properties that are the same for annulus and nucleus. Both tissue models differed in the 3D OVED model only by composition. The composition-based modeling presents the advantage of reducing the numbers of material parameters to a minimum and to use tissue composition directly as input. Hence, this approach provides the possibility to describe internal mechanical conditions of the disc as a function of assessable biophysical characteristics.

An Anisotropic Multiphysics Model for Intervertebral Disk

“…The values of mechanical properties, fluid content, and FCD are assigned uniformly in the NP and CEP, whereas linearly vary from the innermost AF to the outermost AF [41,42]. This approach is different from the approaches in the literature, which usually assign the uniformly distributed mechanical properties to NP, CEP, and AF (or outer AF and inner AF) [14,16]. Our approach also can alleviate numerical oscillation at the interface of AF and NP, which may be generated because of the jump of mechanical properties [43].…”

“…[9][10][11]), the biphasic/ biphasic-swelling model (e.g., Refs. [12][13][14][15][16][17]), and multiphasic mechano-electrochemical model [18][19][20]. The single-phase model treats the NP as an ideal fluid and the AF as a solid, which cannot characterize the interstitial fluid flow in the AF and swelling pressure [9].…”

Design of next generation total disk replacements

“…The osmotic nucleus swells and prestresses the annular fibers. It allows for creep and stress relaxation (Schroeder et al, 2006;Schroeder et al, 2010), for a diurnal cycle of swelling and shrinking, and for poro-visco-elastic behavior. Hence, the IVD is a deformable body, allowing flexibility under low loads, and restricted motion under high loads, protecting surrounding tissues against overloading.…”

A database of lumbar spinal mechanical behavior for validation of spinal analytical models

“…Finite element models have been used to gain understanding of elastic load-deformation behavior [Dreischarf et al 2014, Weisse et al 2012], time-dependent behavior [Castro et al 2014, Galbusera et al, 2011, Schmidt et al 2013, Schroeder et al 2010] and insights into damage accumulation [Qasim et al 2012], degeneration and transport of nutrients and metabolites [Natarajan, Williams and Andersson (2004), Schmidt et al, 2013]. Models are also used to predict the behavior of surgical implants [Zhang and Teo 2008], and in multi-segmental spine models to estimate in vivo spinal and muscular forces with each motion segment represented by a stiffness matrix or equivalent beam [Gardner-Morse and Stokes 2004].…”