Non-invasive Determination of Ankle Rotation Axes Using a Robotic Gyroscopic Mechanism

Among four joints of human foot in the ankle area, the tibiotalar and subtalar joints play the most important role in making it possible for the foot to perform rotational movements such that kinematic behavior of foot is almost completely affected by orientation of their rotation axes. Deviation of the axis of rotation from the normal position can impair the function of the ankle and even the lower extremity. In this study, a new non-invasive method has been proposed, through which, using a gyroscopic mechanism, the orientation of the rotation axes of the tibiotalar and subtalar joints can be determined. This method is based on indirect data acquisition from the kinematic behavior of the foot. Using the calculated matrices and through the optimization method, the orientation and position of the rotation axes were respectively calculated at relatively high precision. These results were also assessed in practice by building an ankle mechanical model and a robotic gyroscopic mechanism which is used as a robotic rehabilitation device for ankle rehabilitation. Obtained results show that the maximum error in determining the orientation of the rotation axes is about 2 degrees.