MECHANICAL-PROPERTIES OF CANINE ARTICULAR-CARTILAGE ARE SIGNIFICANTLYALTERED FOLLOWING TRANSECTION OF THE ANTERIOR CRUCIATE LIGAMENT

The compressive, tensile, and swelling properties of articular cartila ge were studied at two time periods following transection of the anter ior cruciate ligament in the knee of greyhound dogs. An experimental p rotocol was designed to quantify the essential equilibrium and biphasi c material properties of cartilage in tension, compression, and shear, as well as the parameters of isometric swelling behavior. All propert ies were measured at several sites to elicit differences between sites of frequent and less frequent contact. Hydration was determined at ea ch site and was compared with the material properties of cartilage fro m corresponding sites. There were extensive changes in all compressive , tensile, and swelling properties of cartilage after transection of t he anterior cruciate ligament. Twelve weeks after surgery, the intrins ic moduli were reduced significantly in compression (approximately 24% of control values), tension (approximately 64%), and shear (approxima tely 24%), and the hydraulic permeability was elevated significantly ( approximately 48%). Significant increases in hydration (approximately 9%) also were observed, as well as a strong correlation of hydration w ith hydraulic permeability. The pattern of these changes was not found to differ with site in the joint, but significant differences were ob served in the magnitude of change for cartilage from the femoral groov e and the femoral condyle. The pattern and extent of changes in the ma terial properties following transection of the anterior cruciate ligam ent indicate that altered loading of the joint severely compromises th e overall mechanical behavior of articular cartilage. The observed los s of matrix stiffness in compression, tension, and shear is associated with increases in the deformation of the solid matrix, a diminished a bility to resist swelling, and the increase in hydration observed in t his study. The increased swelling and elevated water content were rela ted directly to the increase in hydraulic permeability; this suggests an associated loss of fluid pressurization as the load support mechani sm in the degenerated cartilage. Without a successful mechanism for re pair, damage to the solid matrix may progress and lead to further dege nerative changes in the biochemistry, morphology, and mechanical behav ior of articular cartilage.