Tribological and material properties for cartilage of and throughout the bovine stifle: support for the altered joint kinematics hypothesis of osteoarthritis

Abstract

Prior studies suggest that ligament and meniscus tears cause osteoarthritis (OA) when changes in joint kinematics bring underused and underprepared regions of cartilage into contact. This study aims to test the hypothesis that material and tribological properties vary throughout the joint according to the local mechanical environment. The local tribological and material properties of bovine stifle cartilage (N=10 joints with 20 samples per joint) were characterized under physiologically consistent contact stress and fluid pressure conditions. Overall, cartilage from the bovine stifle had an equilibrium contact modulus of Ec0=0.62±0.10MPa, a tensile modulus of Et=4.3±0.7MPa, and a permeability of k=2.8±0.9×10(-3)mm(4)/Ns. During sliding, the cartilage had an effective friction coefficient of μeff=0.024±0.004, an effective contact modulus of Ec=3.9±0.7MPa and a fluid load fraction of F'=0.81±0.03. Tibial cartilage exhibited significantly poorer material and tribological properties than femoral cartilage. Statistically significant differences were also detected across the femoral condyle and tibial plateau. The central femoral condyle exhibited the most favorable properties while the uncovered tibial plateau exhibited the least favorable properties. Our findings support a previous hypothesis that altered loading patterns can cause OA by overloading underprepared regions. They also help explain why damage to the tibial plateau often precedes damage to the mating femoral condyle following joint injury in animal models. Because the variations are driven by fundamental biological processes, we anticipate similar variations in the human knee, which could explain the OA risk associated with ligament and meniscus tears.