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

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 enclos-es 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 am-bulation 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.

Automated summary

Robotic leg prostheses that replicate the biomechanical functions of the missing biological leg have the potential to improve mobility and quality of life for lower-limb amputees. However, existing powered prostheses are heavier, bigger, and have shorter battery life compared to passive prostheses, which limits their clinical viability. In this study, researchers present a robotic leg prosthesis that replicates the key biomechanical functions of the knee, ankle, and toe while matching the weight, size, and battery life of conventional prostheses. Preclinical tests show that this prosthesis allows for common ambulation activities with close to normative kinematics and kinetics, and users can walk on level ground indefinitely without charging the battery in passive mode.