Long-Term Performance and User Satisfaction With Implanted Neuroprostheses for Upright Mobility After Paraplegia: 2- to 14-Year Follow-Up

Abstract

Objective: To quantify the long-term (>2y) effects of lower extremity (LE) neuroprostheses (NPs) for standing, transfers, stepping, and seated stability after spinal cord injury.

Design: Single-subject design case series with participants acting as their own concurrent controls, including retrospective data review.

Setting: Hospital-based clinical biomechanics laboratory with experienced (>20y in the field) research biomedical engineers, a physical therapist, and medical monitoring review.

Participants: Long-term (6.2±2.7y) at-home users (N=22; 19 men, 3 women) of implanted NPs for trunk and LE function with chronic (14.4±7.1y) spinal cord injury resulting in full or partial paralysis.

Interventions: Technical and clinical performance measurements, along with user satisfaction surveys.

Main outcome measures: Knee extension moment, maximum standing time, body weight supported by lower extremities, 3 functional standing tasks, 2 satisfaction surveys, NP usage, and stability of implanted components.

Results: Stimulated knee extension strength and functional capabilities were maintained, with 94% of implant recipients reporting being very or moderately satisfied with their system. More than half (60%) of the participants were still using their implanted NPs for exercise and function for >10min/d on nearly half or more of the days monitored; however, maximum standing times and percentage body weight through LEs decreased slightly over the follow-up interval. Stimulus thresholds were uniformly stable. Six-year survival rates for the first-generation implanted pulse generator (IPG) and epimysial electrodes were close to 90%, whereas those for the second-generation IPG along with the intramuscular and nerve cuff electrodes were >98%.

Conclusions: Objective and subjective measures of the technical and clinical performances of implanted LE NPs generally remained consistent for 22 participants after an average of 6 years of unsupervised use at home. These findings suggest that implanted LE NPs can provide lasting benefits that recipients value.

Trial registration: ClinicalTrials.gov NCT00004445 NCT00623389 NCT01474148 NCT01570816.

Keywords: Electric stimulation; Lower extremity; Neural prostheses; Rehabilitation; Spinal cord injuries.

Conflict of interest statement

The authors do not have any conflicts of interest.

Published by Elsevier Inc.

Figures

Figure 1

NP system components. (Note that panels are not to the same scale.) (a) External control unit, fingerswitch, and transmitting coil.* (b) Implanted pulse generator. (c) Intramuscular, nerve cuff, and epimysial electrodes. * Photo credit: Nathaniel Welch.

Figure 2

Three functional tasks were tested: standing (a), standing to retrieving an object from an overhead shelf (b), and performing a standing pivot transfer (c). Additionally, 3 participants with incomplete SCI could walk using their NP (d).

Figure 2

Three functional tasks were tested: standing (a), standing to retrieving an object from an overhead shelf (b), and performing a standing pivot transfer (c). Additionally, 3 participants with incomplete SCI could walk using their NP (d).

Figure 3

Stability of electrodes from 22 participants in terms of increases of muscle activation threshold at LT follow-up.