Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

The purposes of this study were to determine the in situ functional and mat erial properties of articular cartilage in an experimental model of joint i njury, and to quantify the corresponding in situ joint contact mechanics. E xperiments were performed in the anterior cruciate ligament (ACL) transecte d knee of the cat and the corresponding, intact contralateral knee, 16 week s following intervention. Cartilage thickness, stiffness, effective Young's modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral j oint were obtained in situ using Fuji Pressensor film, and comparisons betw een experimental and contralateral joint were made for corresponding loadin g conditions. Total joint contact area and peak pressure were increased and decreased significantly (alpha = 0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stif fness were increased and decreased significantly (alpha = 0.01), respective ly, in the experimental compared to the contralateral joint in the four fem oral and patellar test locations. Articular cartilage material properties ( effective Young's modulus and permeability) were the same in the ACL-transe cted and intact joints. These results demonstrate for the first time the ef fect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corr oborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of ca rtilage properties and joint surface geometry from the experimental animals . We conclude that the joint contact mechanics in the ACL-transected cat ch ange within 16 weeks of experimental intervention. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.