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Are disc pressure, stress, and osmolarity affected by intra‐ and extrafibrillar fluid exchange?
Author(s) -
Schroeder Yvonne,
Sivan Sarit,
Wilson Wouter,
Merkher Yulia,
Huyghe Jacques M.,
Maroudas Alice,
Baaijens Frank P.T.
Publication year - 2007
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.20443
Subject(s) - osmotic pressure , hydrostatic pressure , osmotic concentration , mechanics , biology , physics , biochemistry
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. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1317–1324, 2007