The Instantaneous Axis of Rotation of the Foot and Ankle Based on Kinematic Data of a Two-Segment Model

Several mathematic methods for locating the instantaneous center of rotation of a rigid body have been reported. However, the basic Reuleaux method remains planar in nature and susceptible to position signal noise of marker coordinate data. A mathematical method and algorithm for determining the mean, 30 instantaneous axis of rotation (IAOR) for the foot and ankle during gait is presented. The method employs kinematic marker data in order to describe the instantaneous axis of rotation of the calcaneus with respect to the tibia. Results from validation procedures demonstrate the applicability of the method. Analysis of foot and ankle gait data indicated the reliability of the method