The physical properties of articular cartilage depend on the water content. Therefore, the growth of the degeneration of osteoarthritic cartilage can be evaluated nondestructively and quantitatively by measuring the water content using a near infrared (NIR) spectroscopic meter. The relation between the reflected light intensity at the absorption wavelength and water content in gelatin and normal human articular cartilage was experimentally investigated. The scattering behavior of NIR in the cartilage was also theoretically investigated by Monte Carlo method and compared to the experimental results. The gelatin showed a correlation between water content and reflected light intensity, but no correlation between them was found in the cartilage. The simulation showed that the average penetration depth of the NIR was 0.2mm, and the reflected light intensity was strongly influenced by water content in the surface layer. Good correlation between water content in the surface layer and reflected light intensity was also derived from the simulation.

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