Authors: Kyle R. Embry, Lorenzo Vianello, Jim Lipsey, Frank Ursetta, Michael Stephens, Zhi Wang, Ann M. Simon, Andrea J. Ikeda, Suzanne B. Finucane, Shawana Anarwala, Levi J. Hargrove
Organizations: Center for Bionic Medicine, Shirley Ryan AbilityLab, Chicago, IL, USA · Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA · Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA
Lower limb amputation affects millions worldwide, leading to impaired mobility, reduced walking speed, and limited participation in daily and social activities. Powered prosthetic knees can partially restore mobility by actively assisting knee joint torque, improving gait symmetry, sit-to-stand transitions, and walking speed. However, added mass from powered components may diminish these benefits, negatively affecting gait mechanics and increasing metabolic cost. Consequently, optimizing mass distribution, rather than simply minimizing total mass, may provide a more effective and practical solution. In this exploratory study, we evaluated the feasibility of above-knee powertrain placement for a powered prosthetic knee in a small cohort. Compared to below-knee placement, the above-knee configuration demonstrated improved walking speed (+9.2% for one participant) and cadence (+3.6%), with mixed effects on gait symmetry. Kinematic measures indicated similar knee range of motion and peak velocity across configurations. Additional testing on ramps and stairs confirmed the robustness of the control strategy across multiple locomotion tasks. These preliminary findings suggest that above-knee placement is functionally feasible and that careful mass distribution can preserve the benefits of powered assistance while mitigating adverse effects of added weight. Further studies are needed to confirm these trends and guide design and clinical recommendations.
Figures & tables
Fig. 1 : Powered Knee Placement. In this work, we present preliminary example of above knee powertrain placement (right) and compare it to conventional below-knee powertrain placement (left).
Fig. 2 : Comparison with commercially available Powered Prosthetic Devices. From left to right, Intuy Knee [ 4 ] , the Össur Power Knee [ 17 ] , the BionicM BioLeg [ 20 ] , and our prototype.
Subject ID
Age [yrs]
Time since amputation [y]
Gender
Etiology
Height [cm]
Weight [kg]
K-level
Osseointegrated
TF01
49.9
47.4
M
Trauma
190.5
106.1
K4
N
TF02
31.6
16.2
M
Sarcoma
171.5
88.6
K3
Y
TF03
50.4
1.6
M
Trauma
182.9
87.3
K3
Y
TABLE I : Participants demographics: From left to right: the Subject Identifier; the Age at intake, namely the participant’s age at the time of enrollment in the study; Time since amputation. K-level refers to the Medicare Functional Classification Level, indicating the participant’s mobility potential (K3 = community ambulator with variable cadence, K4 = active adult or athlete). Osseointegrated indicates whether the patient underwent osseointegration and uses an osseointegrated (OI) interface rather than a conventional socket.
Fig. 3 : Comparison of Kinematic during level-ground walking for Above-Knee (green) and Below-knee (orange) powertrain placement for both TF01 (left) and TF02 (right).The plot displays the mean (solid line) and the ± standard deviation region, shown as a shaded area, across all strides. From top to bottom: Knee position and velocity measured by knee encoder, Vertical force and saggital moment measured by the load-cell. On the x-axis the gait phase in percent between two consecutive heelstrikes.
Fig. 4 : Walking Speed (m/s) and Cadence (steps/min) for each participant and condition (Self-selected and Fast speed), measured using the pressure-sensitive walkway. Above-Knee placement is shown in green, and Below-Knee placement in orange. For both walking speed and cadence, higher values indicate respectivelly higher walking speed and cadence.
Fig. 5 : Gait symmetries measured with pressure-sensitive walkway for participants TF01 and TF02: Above-Knee configuration is shown in green, and Below-Knee prosthetic placement in orange. From top to bottom and left to right, the plots display symmetries for: step time, step length, swing phase percentage, stance phase percentage, and step width. Higher values indicate more symmetric behavior between the two legs.
Fig. 6 : Subject TF03 performed multiple activities while wearing the prosthetic device in Above-Knee configuration. Here we display a representative example of the user joint kinematic while performing ramp ascending and descending as well as stairs ascending and descending.
Department of Mechanical Engineering, University of Jaffna, Sri Lanka · Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey, 07102, USA
Woodruff School of Mechanical Engineering and the Institute for Robotics and Intelligent Machines, Georgia Institute of Technology, Atlanta, GA 30332-0405 USA · Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 USA