Workflow assessing the effect of gait alterations on stresses in the medial tibial cartilage - combined musculoskeletal modelling and finite element analysis.

Knee osteoarthritis (KOA) is most common in the medial tibial compartment. We present a novel method to study the effect of gait modifications and lateral wedge insoles (LWIs) on the stresses in the medial tibial cartilage by combining musculoskeletal (MS) modelling with finite element (FE) analysis. Subject's gait was recorded in a gait laboratory, walking normally, with 5° and 10° LWIs, toes inward ('Toe in'), and toes outward ('Toe out wide'). A full lower extremity MRI and a detailed knee MRI were taken. Bones and most soft tissues were segmented from images, and the generic bone architecture of the MS model was morphed into the segmented bones. The output forces from the MS model were then used as an input in the FE model of the subject's knee. During stance, LWIs failed to reduce medial peak pressures apart from Insole 10° during the second peak. Toe in reduced peak pressures by -11% during the first peak but increased them by 12% during the second. Toe out wide reduced peak pressures by -15% during the first and increased them by 7% during the second. The results show that the work flow can assess the effect of interventions on an individual level. In the future, this method can be applied to patients with KOA.

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.