Method for estimating three-dimensional knee rotations with inertial measurement units

This study seeks to validate a method for measuring three-dimensional knee rotations with inertial measurement units (IMUs) on human subjects and with measurements from optical motion capture (MOCAP). Unlike a prior validation conducted with an instrumented mechanical linkage, experiments on human subjects incur challenges arising from imprecise determination of the thigh and shank anatomical axes, laxity of the knee, superimposed motions of the underlying soft tissues, among others. The cornerstone of this method is correcting drift error in IMU orientations by exploiting the natural kinematic constraints of a human knee. The results herein demonstrate promise for long-term, non-invasive monitoring of knee rotations in naturalistic settings.