Effects of mechanical compression on metabolism and distribution of oxygen and lactate in intervertebral disc

Abstract

The objective of this study was to examine the effects of mechanical compression on metabolism and distributions of oxygen and lactate in the intervertebral disc (IVD) using a new formulation of the triphasic theory. In this study, the cellular metabolic rates of oxygen and lactate were incorporated into the newly developed formulation of the mechano-electrochemical mixture model [Huang and Gu, J. Biomech. Eng., 129:423-429, 2007]. The model was used to numerically analyze metabolism and transport of oxygen and lactate in the IVD under static or dynamic compression. The theoretical analyses demonstrated that compressive loading could affect transport and metabolism of nutrients. Dynamic compression increased oxygen concentration, reduced lactate accumulation, and promoted oxygen consumption and lactate production (i.e., energy conversion) within the IVD. Such effects of dynamic loading were dependent on strain level and loading frequency, and more pronounced in the IVD with less permeable endplate. In contrast, static compression exhibited inverse effects on transport and metabolism of oxygen and lactate. The theoretical predictions in this study are in good agreement with those in the literature. This study established a new theoretical model for analyzing cellular metabolism of nutrients in hydrated, fibrous soft tissues under mechanical compression.

Investigation of solute concentrations in a 3D model of intervertebral disc

“…The computed minimum oxygen concentration of 0.43 kPa, found for the reference case (i.e., fully permeable CEPs) at the antero- lateral region of the inner AF, falls within measured range of 0.3-1.1 kPa [20] and 0.53-1.06 kPa [16]. It is; however, lower than 0.75 kPa computed at the nucleus centre in our earlier axisymmetric model studies [33] and 0.49 kPa [22] evaluated in an axisymmetric disc with 50% permeable end-plate adjacent to the NP under a 10% nominal axial compressive strain. The computed maximum lactic concentration of 5.45 nmol/mm 3 at the antero-lateral region of AF is also within the measured range of 2-6 nmol/mm 3 [5] but greater than the maximum predictions of 4.56 nmol/ mm 3 at the nucleus center [33] and 4.38 nmol/mm 3 in the AF region [22] using axisymmetric models.…”

“…It is; however, lower than 0.75 kPa computed at the nucleus centre in our earlier axisymmetric model studies [33] and 0.49 kPa [22] evaluated in an axisymmetric disc with 50% permeable end-plate adjacent to the NP under a 10% nominal axial compressive strain. The computed maximum lactic concentration of 5.45 nmol/mm 3 at the antero-lateral region of AF is also within the measured range of 2-6 nmol/mm 3 [5] but greater than the maximum predictions of 4.56 nmol/ mm 3 at the nucleus center [33] and 4.38 nmol/mm 3 in the AF region [22] using axisymmetric models. The extreme glucose concentration of 0.94 nmol/mm 3 at the nucleus/ annulus interface compares with 0.5-2.5 nmol/mm 3 measured in scoliotic disc annuli [9].…”

“…These geometries also place restrictions on realistic simulation of conditions of interest such as local endplate fractures/calcifications and changes in the posture. Recent model studies of disc nutrition under compression, while neglecting the upper and lower cartilaginous end-plates, have either assumed an axisymmetric geometry [22] or considered a 3D geometry but with a constant height along the disc and a single nonmetabolised solute [50]. Hence, the primary objective of this study is to develop a novel, fully 3D finite element model (FEM) of a lumbar L5-S1 disc to investigate the solute transport within the disc tissue under different conditions.…”

The effects of dynamic loading on the intervertebral disc

“…Diurnal cyclic compression enhanced transport of a 3 kDa dextran solute into the disc through the endplates in an ovine disc culture model [28]. Dynamic compression (0.1 Hz, 10% strain, 200 cycles) increased oxygen concentration and decreased lactate concentration in the disc than the unloaded samples in a study using a finite element model [39]. These results imply that dynamic loading may improve the transport of solutes through the disc and hence affecting the metabolism of the disc.…”

Disc size markedly influences concentration profiles of intravenously administered solutes in the intervertebral disc: a computational study on glucosamine as a model solute

“…Few hours of static loading have been found in vivo to inhibit transport [27]. Model studies of transport accounting for solute convection generally indicate minor effects in static compression [13,[28][29][30][31] but either negligible [29] or moderate [30,31] effects under cyclic compression loads.…”