Effect of bone inhomogeneity on tibiofemoral contact mechanics during physiological loading.

It is not known how inhomogeneous mechanical properties of bone affect contact mechanics and cartilage response during physiological loading of the knee joint. In this study, a finite element model of a cadaver knee joint was constructed based on quantitative computed tomography (QCT). The mechanical properties of bone were altered and their effect on tibiofemoral contact mechanics and cartilage stresses, strains and pore pressures were evaluated during the first 20% of stance. For this purpose, models with rigid, homogeneous and inhomogeneous bones were created. When bone was modeled to be rigid, the resulting contact pressures were substantially higher in the medial side of the joint, as compared to the non-rigid bones. Similar changes were revealed also in stresses, strains and pore pressures throughout the cartilage depth at the cartilage-cartilage contact area. Furthermore, the mechanical response of medial tibial cartilage was found to be highly dependent on the bone properties. When Young׳s modulus in the model with homogeneous bone was 5GPa, cartilage mechanical response approached to that of the model with inhomogeneous bone. Finally, when the apparent bone mineral densities were decreased globally in the inhomogeneous bone, stresses, strains and pore pressures were decreased at all layers of medial tibial cartilage. Similar changes were observed also in cartilage-cartilage contact area of the lateral compartment but with a lesser extent. These results indicate that during physiological loading Young׳s modulus of bone has a substantial influence on cartilage stresses and strains, especially in the medial compartment.