Effect of hydration on the frequency-dependent viscoelastic properties of articular cartilage.

The aim of this study was to determine the effect of tissue hydration on the frequency-dependant viscoelastic properties of articular cartilage. Such changes were determined at frequencies associated with normal (1-10 Hz) and impulsive/traumatic (90 Hz) heel-strike times. Cartilage on bone samples, obtained from bovine humeral heads, was tested when hypo-hydrated and hyper-hydrated using dynamic mechanical analysis. Dynamic mechanical analysis was performed at a range of frequencies between 1 and 90 Hz. Hypo-hydration increased the stiffness of cartilage as compared to hyper-hydrated cartilage; this increase was greater at higher frequencies. The storage modulus and stiffness increased in hypo-hydrated cartilage as compared to hyper-hydrated cartilage. However, the loss modulus and stiffness increased when cartilage was hypo-hydrated as compared to hyper-hydrated, but these increases were not frequency dependent. An impulsive heel-strike time may result in a greater increase of stiffness in hypo-hydrated cartilage, compared with hyper-hydrated cartilage. However, the ratio of storage to loss stiffness was greater for hyper-hydrated cartilage, thereby, reducing the tissue's ability to dissipate energy and increasing the likelihood of cartilage rupture.