Figure 1 (A) Features of the device including: knee transmission with encoder (top right), ankle transmission with encoder (top left), ELMO motion controller (middle right), microprocessor (middle right), height-adjustable shank (middle left), and 6-DOF load cell (bottom left). (B) User walking with a prosthetic device on a ramp.
Photograph published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2019.
A study was conducted to validate an impedance control strategy for a powered knee and ankle prosthesis that would improve locomotion and asymmetric loading between the intact and residual limb joints among people who use transfemoral prostheses during level walking and when ascending or descending slopes. The research team concluded that the strategy, which used an embedded sensor suite of encoders and a six-axis load cell, had the ability to assist users when ambulating over different conditions in a safe, seamless, and natural manner.
The investigators developed a device that had one actuated degree of freedom (DOF) at the knee joint in the sagittal plane, and two DOFs at the ankle—a powered DOF in the sagittal plane and a passive DOF in the frontal plane. The device with the battery weighs approximately 7.5kg and has adjustable build heights of 46-63cm to accommodate different residual limb lengths.
To test whether the dual-powered knee and ankle prosthesis could generate appropriate device joint kinematics across users, seven people with transfemoral amputations participated: three walked on a treadmill and four walked on a ramp circuit.
The device’s controller recognized the different phases of gait, tuned joint impedance across a range of gait speeds/inclination angles, and generated knee and ankle kinematics similar to individuals without amputations. The controller correctly recognized 6,348 phase transitions across both walking speeds and inclination angles demonstrating the ability to render correct transitions to ensure reliable gait, according to the study’s authors,
The researchers found that tuning two to three subject-specific parameters per ambulation mode was necessary to deliver individualized assistance.
The open-access study was published in the January-February Supplement of Military Medicine.
