A lightweight robotic leg prosthesis replicating the biomechanics of the knee, ankle, and toe joint

Abstract

Robotic leg prostheses promise to improve the mobility and quality of life of millions of individuals with lower-limb amputations by imitating the biomechanics of the missing biological leg. Unfortunately, existing powered prostheses are much heavier and bigger and have shorter battery life than conventional passive prostheses, severely limiting their clinical viability and utility in the daily life of amputees. Here, we present a robotic leg prosthesis that replicates the key biomechanical functions of the biological knee, ankle, and toe in the sagittal plane while matching the weight, size, and battery life of conventional microprocessor-controlled prostheses. The powered knee joint uses a unique torque-sensitive mechanism combining the benefits of elastic actuators with that of variable transmissions. A single actuator powers the ankle and toe joints through a compliant, underactuated mechanism. Because the biological toe dissipates energy while the biological ankle injects energy into the gait cycle, this underactuated system regenerates substantial mechanical energy and replicates the key biomechanical functions of the ankle/foot complex during walking. A compact prosthesis frame encloses all mechanical and electrical components for increased robustness and efficiency. Preclinical tests with three individuals with above-knee amputation show that the proposed robotic leg prosthesis allows for common ambulation activities with close to normative kinematics and kinetics. Using an optional passive mode, users can walk on level ground indefinitely without charging the battery, which has not been shown with any other powered or microprocessor-controlled prostheses. A prosthesis with these characteristics has the potential to improve real-world mobility in individuals with above-knee amputation.

Can a powered knee-ankle prosthesis improve weight-bearing symmetry during stand-to-sit transitions in individuals with above-knee amputations?

“…However, the damping systems implemented in these microprocessor-controlled prostheses are limited in their ability to accurately control the resistive joint torque and to dissipate large amounts of energy, especially at large exion angles [6]-[8], [47]. Using their embedded actuators, powered prostheses can more precisely control the joint torque while dissipating large amounts of energy, even at large knee exion angles [33]. This study tested the hypothesis that a powered prosthesis can improve weight-bearing symmetry and reduce muscle effort during sit-down compared to passive prostheses by providing higher resistive torque at the prosthetic knee joint.…”

“…Both the knee and ankle can provide up to 150 Nm of torque in exion or extension during movements. The prosthesis, including the powered knee module, powered ankle/foot module, batteries, and protective covers, weighs 3.2 kg [33]. The powered knee module uses a novel torque-sensitive actuator.…”

“…The powered knee module uses a novel torque-sensitive actuator. The powered ankle/foot module has joints at the ankle and toe which are both actuated by a single actuator [33]. A custom instrumented pyramid adapter was attached to the top of the ankle module to estimate the vertical ground reaction force and sagittal plane torques [37], [38].…”

“…To accomplish these goals, we recruited ten individuals with above-knee amputations. The subjects sat down using their prescribed passive prosthesis and a research powered prosthesis [33] while we recorded joint angles, ground reaction forces, and muscle activity from the intact quadricep muscle. As primary outcomes to test our hypothesis, weightbearing symmetry was measured using the average index of asymmetry of the vertical ground reaction force, and muscle effort was measured using the peak and integral of the intact vastus medialis muscle EMG.…”

A-Mode Ultrasound-Based Prediction of Transfemoral Amputee Prosthesis Walking Kinematics via an Artificial Neural Network

“…potentially address the limitations of passive prosthesis by using their embedded actuators, sensors, and control system. With these powered prostheses, amputees are able to perform activities such as crossing obstacles, squatting, or walking up stairs that are not possible with passive prostheses [3] [4]. Furthermore, activities that are possible with passive prostheses, such as walking, ascending ramps, sitting down, and standing up, can become more efficient with powered prostheses [5][6] [7] [8].…”