Analysis of the Effect of the Knee Moment on Walking Effort in Able-bodied and Below-knee Amputee Gait

In below-knee amputee (bka) gait, many studies report a lower peak knee extension moment in the residual leg, compared to the intact leg and able-bodied gait. Belowknee amputees have a fully functioning knee in their residual leg, so they should be able to have a normal knee moment, which might reduce the high incidence rate of ostheoarthritis in the intact leg. I hypothesize that below-knee amputees have a lower peak extension knee moment to decrease the effort of walking. In able-bodied walking, a decrease in the peak knee extension moment will increase effort, since the knee moment is used to transfer forces from the upper leg to the lower leg. Predictive simulations of gait on a sagittal plane model with different peak knee extension moments are analysed to relate this moment to the effort of walking. The open loop controls of a gait cycle are found by solving an optimal control problem that aims to minimize tracking with respect to normal walking data and minimize the effort of walking. A constraint is added to the optimal control problem to vary the peak knee extension moment. In able-bodied gait, the peak knee extension moment should be lower than this constraint, while in bka gait, the peak knee extension moment should be equal to at least the value of the constraint. No significant increase in effort was found when a constraint was added to the optimal control problem. Next to this, there was a very small decrease in the hip moment in the residual leg in the bka gait. This means that there might be a small positive effect of increasing the peak knee extension moment in bka gait. However, the constraint in bka gait only altered the kinetics of the gait at the time instant where the constraint was applied. Therefore, a more significant difference might be found when one aims to find a gait that has more symmetric joint moments.