The effects of selective matrix degradation on the short-term compressive properties of adult human articular cartilage.

The effects of proteoglycan and collagen digestion on the transient response of human articular cartilage when tested in unconfined compression were determined. Small cylindrical specimens of cartilage, isolated from the femoral head of the hip joint and from the femoral condyles of the knee joint, were subjected to a suddenly applied compressive load using a test apparatus designed to yield a transient oscillatory response. From this response values of the elastic stiffness and the viscous damping coefficient were determined. Cathepsin D and cathepsin B1 were used to digest the proteoglycan in some specimens, while in other specimens leukocyte elastase was used to attack the non-helical terminal regions of the Type II tropocollagen molecules and possibly the Type IX collagen molecule and thereby disturb the integrity of the collagen mesh. The results showed that proteoglycan digestion alone reduced the viscous damping coefficient but it did not significantly alter the elastic stiffness as determined from the oscillatory response. In contrast, the action of elastase reduced both the damping coefficient and the elastic stiffness of the cartilage. The results demonstrated the role of proteoglycans in regulating fluid transport in cartilage and hence controlling the time-dependent viscous properties. The elastic stiffness was shown to be dependent on the integrity of the collagen fibre network and not on the proteoglycans.