Abstract
Intervertebral discs (IVD) provide flexibility to the back and ensure functional distributions of the spinal loads. They are avascular, and internal diffusion-dependent metabolic transport is vital to supply nutrients to disc cells1, but interactions with personalized IVD shapes and mechanics remain poorly explored. Poromechanical finite element models of seven personalized lumbar IVD geometries, with mean heights ranging from 8 to 16 mm were coupled with a reactive oxygen, glucose and lactate transport model linked with tissue deformations and osmosis . In previous studies, reduced formulations of the divergence of the solute flux (∇ .J = ∇ . (D∇ C) = ∇ D. ∇ C +D∇ 2C) ignored the dependence of the diffusion on the deformation gradients, ∇ D. ∇C. We simulated this phenomenon to explore its significance in mechano-metabolic -transport couplings, in the different geometries, over 24h of simulated rest (8h) and physical activity (16h). ∇ D. ∇ C affected the daily variations of glucose concentrations in IVD thinner than 12 mm but with neglectable variation ranges, while not considering ∇ D. ∇ C in taller discs only slightly overestimated the glucose concentration. Most importantly, tall IVD had nearly 60% less glucose than thin IVD, with local drops below the concentration of 0.5 mM, considered to be critical for disc cells3, in the anterior nucleus pulposus. On the one hand, previous reduced formulations for mechanometabolic-transport models of the IVD seem acceptable, even for patient-specific modelling. On the other hand, tall IVD might suffer from unfortunate combinations of deformation-dependent solute diffusion and large diffusion distances, which may favor early
Acknowledgements: Catalan Government and European Commission (2020 BP 00282; ERC-2021-CoG-O-Health-101044828)
