MECHANICAL-BEHAVIOR OF ARTICULAR-CARTILAGE IN SHEAR IS ALTERED BY TRANSECTION OF THE ANTERIOR CRUCIATE LIGAMENT

The flow-independent viscoelastic and equilibrium behaviors of canine articular cartilage were examined with time after transection of the a nterior cruciate ligament. The equilibrium, transient, and dynamic she ar behaviors of cartilage were studied in biaxial compression-torsion testing at two time periods after transection of the anterior cruciate ligament and at two sites on the femoral condyle, in order to test fo r differences between sites of frequent and less frequent contact. Wat er content also was measured in cartilage at sites corresponding to th e areas of mechanical testing. Transection of the anterior cruciate li gament produced significant decreases in all measured moduli of articu lar cartilage tested in equilibrium and dynamic shear and in equilibri um compression; the values for these moduli were 61, 56, and 77% of th e control values, respectively, beginning at 6 weeks following transec tion of the anterior cruciate ligament. There was evidence of increase d energy dissipation of cartilage in shear, with a 13 and 35% increase in tan 6 at 6 and 12 weeks after transection of the anterior cruciate ligament, respectively. Changes in the viscoelastic relaxation functi on of cartilage in shear also were evident at 12 weeks after surgery. In all tissue, there was a significant increase in hydration of approx imately 4% at 6 or 12 weeks after surgery. There was little difference between the material parameters for areas considered to be in frequen t and less frequent contact, with the exception of hydration, which wa s greater for areas of less frequent contact. The observed changes in material properties demonstrate that relatively short periods of joint instability result in significant changes in the flow-independent vis coelastic behavior of articular cartilage, as well as in the intrinsic stiffnesses in compression and shear.