Simulation of water content distributions in degenerated human intervertebral discs

Abstract

The objective of this study was to investigate the spatial and temporal variations of water content in intervertebral discs during degeneration and repair processes. We hypothesized that the patterns of water content distribution in the discs are related to the intensity patterns observed in T2-weighted MRI images. Water content distributions in the mildly (e.g., 80% viable cells in the disc, 2.3% decrease in disc height) and moderately (e.g., 40% viable cells in the disc, 9.3% decrease in disc height) degenerated discs were predicted using a finite element model. The variation of water content in the degenerated discs treated with three biological therapies [i.e., increasing the cell density in the NP (Case I), increasing glycosaminoglycan synthesis rate in the nucleus pulposus (Case II), and decreasing glycosaminoglycan degradation rate in the nucleus pulposus (Case III)] were also predicted. It was found that two patterns of water content distributions, a horizontal region with lower water content at the mid-axial plane of nucleus pulposus and a spot with higher water content at the posterior region, were shown during the degeneration progress for the disc simulated in this study. These two patterns disappeared after treatment in Case I, but in Case II and Case III. The implication of these patterns for the horizontal gray band and high intensity zone in T2-weighted MRI images was discussed. This study provided new guidance to develop a novel method for diagnosing disc degeneration and assessing outcomes of biological therapies with MRI techniques.

Computational Modeling Intervertebral Disc Pathophysiology: A Review

“…Specifically, changes in CEP permeability to nutrients has been operationalized in several ways. In some cases, the boundary concentration of nutrients (both glucose and oxygen) at the CEP was reduced down to 50% ( Kauppila, 1995 ; Selard et al, 2003 ; Malandrino et al, 2014 ), 30% ( Zhu et al, 2012 ; Gu et al, 2014 ), or even 0% ( Zhu et al, 2014 , 2016 , 2017 ) of the normal physiological values. Some other studies simulated the effect of CEP calcification by reducing the CEP exchange area with the nucleus pulposus (NP) and AF (Selard and Urban, 2003), or by reducing its water content ( Soukane et al, 2007 ; Shirazi-Adl et al, 2010 ; Jackson et al, 2011a ), thus reducing solute diffusivity into the core of the IVD tissue.…”

“…For instance, Noailly et al (2007) compared theoretical predictions for spinal range of motion with cadaveric measurements to validate their computational model. Similarly, Zhu et al (2017) also used experimental results for disc water content to validate their computational prediction of disc degeneration. Recently, bioreactor studies have been used to validate finite elements models ( Gatenbein et al, 2015 ).…”

Diffusion-weighted 7.0T Magnetic Resonance Imaging in Assessment of Intervertebral Disc Degeneration in Rats

“…A previous study reported water content to decrease with the degenerative process of the intervertebral disc. [ 23 ]…”

New horizons in spine research: Intervertebral disc repair and regeneration

“…Zhu et al developed a cell‐activity‐coupled mechano‐electrochemical finite element model of the IVD with simulated degenerative changes and biological treatments. IVD spatial water content patterns were found to be very sensitive to degenerative state and to biological treatments that increased cell density, increased glycosaminoglycan synthesis rate, and decreased glycosaminoglycan degradation rate …”

“…IVD spatial water content patterns were found to be very sensitive to degenerative state and to biological treatments that increased cell density, increased glycosaminoglycan synthesis rate, and decreased glycosaminoglycan degradation rate. 19…”