Influence of disc height and strain-dependent solute diffusivity on metabolic transport in patient-personalized intervertebral disc models.

INTRODUCTION

Intervertebral disc (IVD) degeneration is a primary contributor to low back pain, with nutritional stress due to the IVD's avascularity recognized as a key factor. Solute transport within the disc relies predominantly on diffusion, which is governed by tissue morphology and mechanical deformation. However, the interplay between disc geometry, poro-mechanical strain, diffusion, and degeneration remains incompletely characterized. Previous specimen-specific models have captured inter-subject variability in metabolite transport, but the isolated effects of disc height and degeneration-dependent material composition have not been systematically assessed. Moreover, although strain-dependent diffusion coefficients are commonly modeled as porosity functions, the role of intra-element diffusivity gradients , arising under large deformation, has been largely overlooked.

METHODS

The present study focuses on poro-mechanical finite element (FE) models of three patient-personalized L4-L5 lumbar IVD geometries, representing varying heights categorized as , , and IVDs. Three days of physiological mechanical load cycles, comprising 8 hours of rest and 16 hours of activity, were simulated, under both 'healthy' (Pfirrmann grade 1) and degenerated (Pfirrmann grade 3) tissue conditions.

RESULTS

Simulation outcomes demonstrated that a one-third reduction in disc height (relative to medium height) led to increases in oxygen and glucose concentrations and decreases in lactate levels, particularly in the nucleus and anterior regions. Conversely, a one-third height increase resulted in reductions in oxygen and glucose and a corresponding rise in lactate levels. These deviations were more pronounced in degenerated tissues, highlighting the synergistic role of morphology and matrix integrity in determining metabolic homeostasis. Importantly, the inclusion of in the diffusion-reaction model produced negligible changes in solute concentration profiles.

DISCUSSION

These findings underscore the predominant influence of disc geometry and matrix composition on IVD metabolic homeostasis, suggesting limited relevance of the term in practical simulations. Simplified diffusion models, without , may be sufficient for future IVD mechano-transport FE modeling.