Comparison Between the Kinematic Behaviour of Different Prototypes of Prosthetic Leg with Actuated Knee and Ankle Joints

Abstract

Background and Aim: The biggest challenge with today's lower leg prosthetic devices is to climb the stairs in a biologically inspired way. When climbing the stairs, due to the large moments in the knee joint, great forces in the knee occur. Because of the magnitude of these forces, which can be up to six times the weight of a person, it is necessary to use a hydraulic drive with an external power source in the knee and ankle joint. However, most commercially available above-knee prosthetic legs only have actuation in the form of damping in the knee joint. Hence, an amputee is forced to use a healthy leg to advance to each step first while amputated leg follows.Technique: In this paper the kinematic behaviour of three different prototypes is analysed and compared with the movement of a healthy leg. The analysed prototypes each have linear hydraulic actuators in both the knee and the ankle joint. The kinematic analysis focuses on the first step of the stair ascent while progressing with the prosthetic leg first. Prototype P1 has one-way aggregate for combined actuation of both cylinders. Prototype P2 has two-way hydraulic aggregate for combined actuation of the knee and the ankle joint. And finally, the prototype P3 has separate actuation of the knee and ankle joint with two-way hydraulic aggregate.Discussion: Obtained diagrams of kinematics motion show improvement for prototype P3 in comparison to older versions of prosthesis. It can be seen that the prosthetic leg with separately actuated knee and ankle joints shows better results in comparison to the movement of subjects without amputation while climbing the stairs.Clinical relevance: Accurate investigation into the prosthetic biomechanics is crucial in order to develop a device that will make life easier for the final user, the amputees. The overview presented in this paper will guide future developers into designing an even better prosthetic leg.