A monolateral actuation system of a hip articulation is configured to be connected to an orthosis. The monolateral actuation system comprises a motor device arranged to provide assistive torque at a motor axis； a transmission device is connected to the motor axis and arranged for transferring the assistive torque onto an output axis corresponding to an axis of flexion-extension of the hip articulation and parallel to the motor axis. The transmission device includes a cable and first and second pulleys connected to one another by the cable. The first and second pulleys are arranged to extend relative to one another variably. A fixed frame is provided for connecting to the orthosis onto which the motor device and the transmission device are mounted.
