Coefficients of friction,lubricin, and cartilage damage in the anterior cruciate ligament‐deficient guinea pig knee

The coefficient of friction (COF) of articular cartilage is thought to increase with osteoarthritis (OA) progression, and this increase may occur due to a decrease in lubricin concentration. The objectives of this study were to measure the COF of guinea pig tibiofemoral joints with different stages of OA and to establish relationships between COF, lubricin concentrations in synovial fluid, and degradation status using the Hartley guinea pig model. Both hind limbs from 24 animals were harvested: seven 3‐month‐old (no OA), seven 12‐month‐old (mild OA), and 10 that were euthanized at 12 months of age after undergoing unilateral ACL transection at 3 months of age (moderate OA). Contralateral knees served as age‐matched controls. COFs of the tibiofemoral joints were measured using a pendulum apparatus. Synovial fluid lavages were analyzed to determine the concentration and integrity of lubricin using ELISA and Western blot, and the overall articular cartilage status was evaluated by histology. The results showed that the mean COF in the ACL‐deficient knees was significantly greater than that of the no OA (p < 0.01) and mild OA knees (p < 0.01). Lubricin concentrations in the ACL‐deficient knees were significantly lower than that in both of the other groups (p < 0.01). No significant differences in COF or lubricin concentration were found between the no OA and mild OA knees. Histology verified the extent of cartilage damage in each group. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:231–237, 2008