In recent studies (Oloyede and Broom, 1991; Soltz and Ateshian, 1997, 1998) it has been demonstrated from experiment and theory that compressive stresses applied across the surface of articular cartilage are supported primarily by the hydrostatic pressurization of the interstitial fluid, under configurations of confined compression creep and stress-relaxation. This pressurization is sustained for several hundred seconds before it eventually subsides, suggesting a major role for interstitial fluid in protecting the solid collagen-protcoglycan matrix from excessive stresses. In the present study, cartilage fluid pressurization is investigated experimentally and theoretically under sinusoidal loading, since the mechanical environment of articular cartilage during daily living is often cyclical in nature. Investigators have demonstrated that this cyclical loading may cause a biosynthetic response of chondrocytes within the tissue, depending on the frequency and amplitude of the applied stresses or strains (e.g. Gray et al., 1988; Hall et al., 1991; Kim et al., 1995; Parkikinen et al., 1992; Sah et al., 1989). A theoretical solution for cyclical loading in confined compression has been obtained previously (Suh et al., 1995) using the biphasic theory (Mow et al., 1980) and this solution is employed here.

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