Effect of Increasing Assistance From a Powered Prosthesis on Weight-Bearing Symmetry, Effort, and Speed During Stand-Up in Individuals With Above-Knee Amputation

Abstract

After above-knee amputation, the missing biological knee and ankle are commonly replaced with a passive prosthesis, which cannot provide net-positive energy to assist the user. During activities such as sit-to-stand, above-knee amputees must compensate for this lack of power using their upper body, intact limb, and residual limb, resulting in slower, less symmetric, and higher effort movements. Previous studies have shown that powered prostheses can improve symmetry and speed by providing positive assistive power. However, we still lack a systematic investigation of the effect of powered prosthesis assistance. Without this knowledge, researchers and clinicians have no framework for tuning powered prostheses to optimally assist users. Here we show that varying the assistive knee torque significantly affected weight-bearing symmetry, effort, and speed during the stand-up movement in eight above-knee amputees. Specifically, we observed improvements in the index of asymmetry of the vertical ground reaction force at the point approximating maximum vertical center of mass acceleration, the integral of the intact vastus medialis activation measured using electromyography, and the stand-up duration compared to the passive prosthesis. We saw significant improvements in all three metrics when subjects used the powered prosthesis compared to the passive prosthesis. We saw improvements in all three metrics with increasing assistive torque levels commanded by the powered prosthesis. We also observed increased weight-bearing asymmetry at the end of movement, and increased kinematic asymmetry with increasing assistance from the powered prosthesis. These results show that powered prostheses can improve functional mobility, potentially increasing quality of life for millions of people living with above-knee amputations.

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

“…Sit-down and stand-up are related movements, which are both essential for independent living. In our previous study of stand-up with a powered prosthesis, we observed similar improvements in weight-bearing symmetry [ 13 ]. During stand-up the index of asymmetry was measured at an extraction point which is not present during sit-down, and so different methods of extracting IOA metrics were used.…”

“…The desired knee joint position at which the peak torque was reached was set in the controller software to approximately 85% of each subject’s sitting knee angle, similar to able-bodied sit-down biomechanics [ 40 ]. The powered ankle joint was controlled using impedance control, using fixed virtual stiffness (K = 3 Nm/deg) and fixed virtual damping (B = 0.2 Nm/deg/s) similar to our previous work [ 12 , 13 ]. The ankle equilibrium position was controlled as a function of knee position (Fig.…”

“…Different from conventional passive prostheses, powered prostheses can perform positive work and provide positive energy using motors and batteries [ 11 ]. Because of this unique ability, most powered prosthetic research has focused on activities that require performing positive work such as standing up, climbing stairs, and walking [ 12 ], [ 13 ], [ 22 – 25 ], [ 14 – 21 ]. In contrast, activities that require performing only negative work have received much less attention [ 12 ], [ 14 ], [ 19 ], [ 23 ], [ 26 ], [ 27 ].…”

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

“…The knee joint position at which the peak torque was reached was set at approximately 85 percent of each subject's sitting knee angle after [40]. The powered ankle joint was controlled using impedance control, using xed stiffness and damping similar to our previous work [12], [13].…”

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

“…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]. To obtain stable and efficient ambulation, powered prostheses need controllers capable of coordinating the actions of the prosthesis with the movement intention of the user.…”