Evaluation of the effect of collagen network degradation on the frictional characteristics of articular cartilage using a simultaneous analysis of the contact condition.

BACKGROUND: Superficial conditions and integrity of collagen network play an important role on the lubrication performance of articular cartilage. In this work, a technique based on the evanescent waves is used for the evaluation of contact condition during friction tests.
METHODS: The frictional and superficial characteristics of the normal and degraded articular cartilages with high and low concentration of collagenase were evaluated. The optical apparatus was set in order to decrease the intensity of a light reflected at the interface between a prism and specimens when collagen fibers are found near the interface.
FINDINGS: For all conditions, an increase in the attenuation of reflectance as the friction coefficient increases was observed with reasonable correlation. For the specimens degraded with collagenase, low friction and reduced attenuation of reflectance were observed at the beginning of sliding followed by a gradual increase in both friction and attenuation of reflectance. In comparison to the degraded specimens, normal specimens presented high friction at beginning and low friction at the end of test.
INTERPRETATION: The superficial conditions and the presence of water at the articular surface play an important role in the lubrication of synovial joints. The ability to retain water for degraded specimens is impaired due to the loss of proteoglycan observed in the histological sections and hence, their low friction observed at the beginning of the test is not sustained for a long time. The use of evanescent waves demonstrated to be very useful in the analysis of the contact condition of articular cartilage.