Evaluating the Kinematics and Dynamics of Mechanically Passive Prosthetic Knee Joint Mechanisms Using Wearable Sensors

Reding, Rachel 1, 2 ; Tomasi, Jessica 1, 2 ; Cheng, Victoria 1 ; Andrysek, Jan 1, 2

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto; 2. PROPEL Laboratory, Bloorview Research Institute

Human gait is characterized by repetitive legged locomotion, and is frequently analyzed to study movement pathologies. An interesting, yet understudied, clinical population includes transfemoral (above-knee) amputees. This research contributed to the long- term development of the “All-Terrain Knee” (AT-Knee). The AT-Knee is a passive, mechanically-controlled, monocentric knee prosthesis. The main objective of this research was to quantify the kinematics of the AT-Knee’s internal locking mechanism as it related to gait events. A self-contained, portable testing unit was designed that attaches directly to the AT-Knee and communicates the gait and locking mechanism kinematics in a user-friendly manner. The position of the lock was experimentally measured using a proximity sensor. These measures were subsequently outputted to a series of LEDs which illuminated based on a specified voltage threshold (i.e., therein communicating the position of the lock in the anterior-posterior plane). The LED illumination was recorded on video throughout a simulated gait cycle. It was observed that four larger LEDs with a greater amount of dividing space were more distinguishable than a single LED bar-graph with 10 lights. While the reduced number of LEDs decreased the number of discrete measurements of the lock position, the tradeoff was beneficial since the foremost interest included knowing whether the lock was in an open or closed position. A supporting mount for the system was designed in SolidWorks and prototyped using 3D printing. The mount included a self-contained unit that housed all the circuitry in a simple box-like structure. This research laid the groundwork for an advanced testing system for the AT-Knee and, since these efforts, further work has been conducted to simplify the circuitry (i.e., reducing size and weight), as well as replace the LEDs with a single LCD screen for communication purposes. Future research includes implementing the circuitry using a printed circuit board, finalizing the mount design, and utilizing the system in clinical trials with transfemoral amputees.