title: Are disc pressure, stress, and osmolarity affected by intra- and extrafibrillar fluid exchange?
abstract: Because extrafibrillar water content dictates extrafibrillar osmolarity, we aimed to determine the influence of intra- and extrafibrillar fluid exchange on intradiscal pressures and stresses. As experimental results showed that extrafibrillar osmolarity affects intervertebral disc cell gene expression and crack propagation, quantification of the effects of changes in intra- and extrafibrillar fluid exchange is physiologically relevant. Therefore, our 3D osmoviscoelastic finite element (FE) model of the intervertebral disc was extended to include the intra- and extrafibrillar water differentiation. Two simulations were performed, one without intrafibrillar fluid and one with intrafibrillar fluid fraction as a function of the extrafibrillar osmotic pressure. The intrafibrillar fluid fraction as a function of the extrafibrillar osmotic pressure was exponentially fitted to human data and implemented into the model. Because of the low collagen content in the nucleus, no noticeable differences in intradiscal pressure estimation were observed. However, values of extrafibrillar osmolarity, hydrostatic pressure, and the total tissue stress calculated for the annulus were clearly different. Stresses, hydrostatic pressure, and osmolarity were underestimated when the intrafibrillar water value was neglected. As the loading increased, the discrepancies increased. In conclusion, the distribution of pressure and osmolarity in the disc is affected by intra- and extrafibrillar water exchange.
authors.affiliation: Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands. y.schroeder@tue.nl
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Schroeder
authors.forename: Sarit
authors.initials: S
authors.lastname: Sivan
authors.forename: Wouter
authors.initials: W
authors.lastname: Wilson
authors.forename: Yulia
authors.initials: Y
authors.lastname: Merkher
authors.forename: Jacques M
authors.initials: JM
authors.lastname: Huyghe
authors.forename: Alice
authors.initials: A
authors.lastname: Maroudas
authors.forename: Frank P T
authors.initials: FP
authors.lastname: Baaijens
mesh_terms: D001834:Body Water / Q000737:chemistry / Q000378:metabolism*; D003198:Computer Simulation; D024022:Fibrillar Collagens / Q000737:chemistry / Q000378:metabolism*; D018495:Fluid Shifts / Q000502:physiology*; D006801:Humans; D007403:Intervertebral Disc / Q000737:chemistry / Q000502:physiology*; D040542:Mechanotransduction, Cellular / Q000502:physiology; D008954:Models, Biological; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D024022:Fibrillar Collagens