Proximal powered knee placement: a case study

TL;DR

Evaluated above-knee powertrain placement for a powered prosthetic knee in a small cohort suggests 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.

Abstract

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 (6)

• Figure 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).
• Figure 2: Comparison with commercially available Powered Prosthetic Devices. From left to right, Intuy Knee elery2020design, the Össur Power Knee ossur_power_knee, the BionicM BioLeg bionicm_bioleg, and our prototype.
• Figure 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 $\pm$ 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.
• Figure 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.
• Figure 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.