Mechanical Behavior of the Human Ankle in the Transverse Plane While Turning

In order to better rehabilitate lower limb amputees, prosthetic technology needs to facilitate turning gait by providing torsional control in the transverse plane. This paper characterizes biological ankle function in the transverse plane during turning gait with simple mechanical elements to assist in the design of a biomimetic prosthetic ankle joint. Motion capture data was collected from ten subjects performing left and right turns through a 90 hallway corner. The initiation, apex, and termination steps of the turn were investigated. The data for each step was separated into several states, and passive elements were chosen to model the ankle in each state. During the first state of each turning step, the ankle behaved similarly to straight steps by limiting the kinetic energy of the foot prior to foot flat. During the subsequent states of each turning step, the ankle altered its characteristic properties to accommodate the curved trajectory of the body center of mass. The results suggest controlling transverse plane stiffness with a finite state control system will suffice to mimic biological function during a turn.