On the conditional equivalence of chemical loading and mechanical loading on articular cartilage

Osmotic pressure loading of articular cartilage has been customarily invoke d to be equivalent to mechanical loading. Tn the literature, this equivalen ce is defined by the amount of water squeezed from the tissue, i.e. if the amount of water content lost by these two modes of loading are the same, it has been generally regarded that the two loadings are equivalent. This ass umption has never been proven. Using the water content lost concept, in thi s paper, we derived the exact conditions under which an osmotic pressure lo ading of cartilage can be considered to be equivalent to a mechanical loadi ng. However, the mechanical loading condition satisfying this equivalancy c riterion, i.e. an isotropic loading delivered via a porous-permeable rigid platen uniformily applied all around the specimen, is not practically achie vable. Moreover, even if this were achieved experimentally, the interstitia l fluid pressure caused by the two loading conditions are not the same. Thi s result has important ramifications for interpretation of experimental dat a from mechanical stimulations of cartilage explant studies. (C) 1998 Elsev ier Science Ltd. All rights reserved.