Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Design of a Smart Prosthetic Liner Controlled by Muscle Activation Feedback

Principal Investigator: Steven A. Gard, PhD

Co-Investigators: Noah Rosenblatt, PhD (Rosalind Franklin University); Farid Amirouche, PhD (University of Illinois-Chicago); Rebecca Stine, MS

Clinical Faculty: Michael Cavanaugh, CPO

Funded by: Department of Veterans Affairs

Status: In progress

Overview

Smart prosthetic linerProsthetic comfort is rated as one of the most important issues faced by lower-limb amputees and is primarily dictated by fit and pressure at the residual limb/prosthetic socket interface. It is well established that socket fit and pressure can fluctuate throughout the day due to redistribution of fluids and associated volumetric changes within the residual limb. While these changes can be managed by donning or doffing socks, doing so will globally add or remove volume to the entire limb, which could negatively affect local interface pressures. Additionally, though, the pressure characteristics between the socket interface and the soft tissue of the residual limb may be dynamically affected by muscle activity during gait. While muscle activity of lower limb amputees is entrained to the gait cycle, the functional roles of this activity are not entirely clear. For example, while hip extensor and flexor muscles aid in moment production, prolonged activity during stance may be needed to stabilize the joint and maintain socket fit. Muscle activation patterns could also reflect control of dynamic socket pressures as muscle contractions alter the shape of the residual limb and socket pressure. However, the functional relationship between electromyography (EMG) signals of the residual limb in lower limb amputees and socket pressure is currently unknown.

The overall design concept is an instrumented prosthetic socket/residual limb interface (liner) that monitors intrasocket EMG and pressures to appropriately modulate pressures during ambulation so as to optimize comfort and function. We will monitor pressures along the surface of muscles within the prosthetic socket at locations neighboring EMG electrode placement. When the muscle contracts the volume of the nearby muscle and residuum tissue will also change leading to local variations in pressures between the socket and limb. The prototypical device is intended to respond to these changes. In response to EMG, we will inflate/deflate pockets of air that have been retrofit to the socket and aligned with the muscles. Pockets will inflate or deflate using small, lightweight compressors which will be controlled using simple on-board real-time logic. The prototype will demonstrate the ability to manipulate intrasocket pressure based on residual limb EMG.

This proposed study is the initial step in a line of investigations to create an intelligent socket interface (liner) that can modulate intrasocket pressure dynamically based on EMG and pressure. The long-term goal is to design a prosthesis that maximizes patient comfort and, in turn, movement performance and other associated aspects of health-related quality of life. After completion of the proposed work we expect to demonstrate that: 1) across a variety of walking speeds and across the duration of walking for multiple minutes a relationship exists between EMG and intrasocket pressure; 2) the relationship is affected by socket fit; 3) the relationship is independent of gait kinematics and kinetics, and 4) EMG provides unique information regarding comfort and it is possible to use this information to manipulate intrasocket pressure and maximize comfort during gait.

The proposed study is intended to lay the groundwork for a more complete understanding of the relationships among EMG, socket pressure and comfort. Creating a dynamic interface that improves socket comfort and reduces interface pressure would improve overall health of the residual limb by limiting daily limb volume fluctuation, tissue breakdown, blistering and reddening of the skin.