Session: 05-12-01: Robotics, Rehabilitation - I

Paper Number: 87862

87862 - Testing of an Articulated Prosthetic Ankle 

We report on our evaluation of an articulated prosthetic ankle (APxA) with hydro-pneumatic passive-resistive assists with a biologically correct ankle axis. This prototype device has been designed to decrease ankle joint stiffness in stance, improve stability on sloped surfaces, and optimize the joint-axis alignment to enhance symmetry and efficiency in ambulation and sit-to-stand tasks. This case-study aimed to establish the safety and feasibility of APxA by evaluating its performance in walking, sitting, and standing tasks on a single subject.

The subject is a male (183 cm Tall, 121 kg) with a transtibial (TT) amputation. His activity level is classified as a K3 under the Medicare Functional Classification Level system (MFCL). This APxA uses a commercially available prosthetic rotatable pyramid adapter which allows for the attachment of many commercially available feet and facilitates the prosthetic foot's external rotation (independent of the ankle joint axis) to match the patient's biological alignment. An Össur brand LP Vari-flex (26 cm) foot was selected to match the subject's height, mass, and MFCL. Both foot and ankle components are instrumented with two inertial measurement units (Bosch BN0055 IMUs). A 32-bit microcontroller (Adalogger, Adafruit Industries) collects and stores inertial, positional, and acceleration data for later analysis.

A certified prosthetist tuned the alignment of the APxA to match the opposite limb optimally and ensure a proper fitting prosthesis. The subject demonstrated the APxA while walking with various cadences and velocities on level-ground, performed the 10-meter walk test (10MWT) and the 6-minute walk test (6MWT). In addition, the subject completed several timed up-and-go tests (TUGT) and five times sit-to-stand (5XSTS) tests. Kinematic data were obtained using a 24-camera motion capture system, and kinetic data were obtained from two in-floor force plates. Kinematic data analysis revealed that while using the APxA, the hip and knee motions of the amputated side decreased, and ankle motion increased, thus improving the overall kinematic symmetry of both left and right extremities compared to the subject’s physician prescribed prosthesis (RxPx).

When answering the open-ended post-experience questions, the subject mentioned that the improved ankle function of the APxA was a positive attribute of the device as compared to the RxPx. Surprisingly, the subject reported that the APxA felt "lighter" in mass than the RxPx, yet the APxA weighs 0.87 kg more.

In total, the subject walked about 2km at a velocity of 1.34 m/s with improved kinematic symmetry. There were no falls, stumbles or observed toe drags.

This study showed that the prototype functioned correctly and demonstrated the device's viability. Also, the protype improved the subject’s kinematic function in gait, standing, and sitting tasks. These preliminary results demonstrate that the APxA is safe for use on a single K3 TT subject in a controlled environment.  Further, the APxA is  feasible for future clinical testing on a larger sample size.

Presenting Author: Michael Davidson Loma Linda University, School of Allied Health Professions, Department of Rehabilitation Sciences

Presenting Author Biography: Michael Davidson is a PhD candidate in Rehabilitation Sciences at Loma Linda University. He is also an Assistant Professor for the School of Allied Health Professions and School of Medicine. Additionally, Michael is the Clinical Manager of the the Orthotics & Prosthetics Department at Loma Linda University Health. He has a Master of Science in Bioengineering from University of California Riverside, a Master in Public Health from Loma Linda University and a Bachelor of Science in Orthotics & Prosthetics from Cal State Dominguez Hills. He is certified in orthotics & prosthetics.

Authors:

Michael Davidson Loma Linda University, School of Allied Health Professions, Department of Rehabilitation Sciences
Noha Daher Loma Linda University, School of Allied Health Professions
Robert Dudley Loma Linda University, School of Allied Health Professions
Thomas Fryer University California, Riverside - Bourns College of Engineering
Johannes Schaepper Loma Linda University - School of Allied Health Professions
Duc Tran Loma Linda University - Department of Physical Medicine and Rehabilitation