Mechanics of knee meniscus results from precise balance between material microstructure and synovial fluid viscosity

The meniscus plays a crucial role in the biomechanics of the knee, serving as load transmitter, and reducing friction between joints. Understanding the biome-chanics of the meniscus is essential to effective treatments of knee injuries and degenerative conditions. In this study, we used two central meniscus samples extracted from a human knee and acquired high-resolution {micro}-CT images. Using an implicit immersed boundary technique, we reconstructed two 3D computational models of the menisci. By eroding the channels of the original meniscus geometry, we created new microstructures with varying porosities (0.53 to 0.8) whilst preserving the connectivity of the porous structure. We investigate the fluid dynamics of the meniscus using a mesh-free numerical method, considering various inlet pressure conditions and analysing the fluid flow within the microstructures. The results of the original microstructure associated with a physiological dynamic viscosity of synovial fluid are in accordance with biophysical experiments on menisci. Furthermore, the eroded microstructure with a 33% increase in porosity exhibited a remarkable 120% increase in flow velocity. This emphasises the sensitivity of meniscus physiology to porous microstructure properties, showing that detailed computational models can explore physiological and pathological conditions, advancing further knee biomechanics research.