Simultaneous estimation of the path, magnitude and orientation of the femorotibial contact forces using bone geometry constraints: an exploratory numerical study for the stance phase of gait

Abstract

The present study introduced a new method to simultaneously optimize the path, magnitude and orientation of medial and lateral femorotibial contact forces using bone geometry constraints. The new method will be numerically compared to the known contact point method while estimating the muscle and contact forces for the stance phase of a single gait trial. A single generic lower extremity model was modified to allow knee flexion with an instantaneous rotation center. The contact point method simulated medial and lateral contact forces with no limited magnitude and with predefined one-dimensional paths and orientations. The new contact zone method simulated contact forces with a limited magnitude and with two-dimensional paths and orientations constrained by the geometry of the bones. A high and low limit was used to study the effect of limiting the contact force magnitude on the predicted forces. The paths of the contact forces for the contact zone method showed a difference up to 25.5 mm with respect to the contact point model. The contact zone method also allowed for more shear contact forces and for some modulation of the external frontal moment. Further limiting the contact force magnitude induced noticeable differences of muscle forces. The contact zone method allows the path, magnitude and orientation of the femorotibial contact forces to be sensitive to knee bone geometries and to the amount of allowable joint contact force. Such a method is promising in characterizing the contact forces with modified gait, bone geometries and knee strength associated with pathological conditions such as osteoarthritic and ACL-deficiency.