INCOMPRESSIBILITY OF THE SOLID-MATRIX OF ARTICULAR-CARTILAGE UNDER HIGH HYDROSTATIC PRESSURES

The objective of this study was to test the hypothesis that the organi c solid matrix of articular cartilage is incompressible under physiolo gical levels of pressure. Due to its anisotropic swelling behavior, an anisotropic version of the biphasic theory was used to predict the de formation and internal stress fields. This theory predicts that, under hydrostatic loading of cartilage via a pressurized external fluid, a state of uniform hydrostatic fluid pressure exists within the tissue r egardless of the anisotropic nature of the solid matrix. The theory al so predicts that if the solid matrix is intrinsically incompressible, the tissue will not deform under hydrostatic loading conditions. This prediction, i.e., no deformation, was experimentally tested by subject ing specimens of normal bovine articular cartilage to hydrostatic pres sures. A new high pressure hydrostatic loading chamber was designed an d built for this purpose. It was found that normal bovine articular ca rtilage, when subject to hydrostatic pressures up to 12 MPa, does not deform measurably. This experimental finding supports one of the funda mental assumptions of the biphasic theory for cartilage, i.e., the org anic solid matrix of the tissue is intrinsically incompressible when l oaded within the normal physiologic range of pressures. Hydrostatic lo ading has often been used in cartilage explant cultures for tissue met abolism studies. The findings of this study provides an accurate metho d to calculate the states of stress acting on the fluid and solid phas es of the tissue in these hydrostatically loaded explant culture exper iments: and suggest that tissue deformation will be minimal under pure hydrostatic pressurization. (C) 1998 Published by Elsevier Science Lt d. All rights reserved.