Longitudinal performance of a surgically implanted neuroprosthesis for lower-extremity exercise, standing, and transfers after spinal cord injury

Abstract

Objective: To investigate the longitudinal performance of a surgically implanted neuroprosthesis for lower-extremity exercise, standing, and transfers after spinal cord injury.

Design: Case series.

Setting: Research or outpatient physical therapy departments of 4 academic hospitals.

Participants: Subjects (N=15) with thoracic or low cervical level spinal cord injuries who had received the 8-channel neuroprosthesis for exercise and standing.

Intervention: After completing rehabilitation with the device, the subjects were discharged to unrestricted home use of the system. A series of assessments were performed before discharge and at a follow-up appointment approximately 1 year later.

Main outcome measures: Neuroprosthesis usage, maximum standing time, body weight support, knee strength, knee fatigue index, electrode stability, and component survivability.

Results: Levels of maximum standing time, body weight support, knee strength, and knee fatigue index were not statistically different from discharge to follow-up (P>.05). Additionally, neuroprosthesis usage was consistent with subjects choosing to use the system on approximately half of the days during each monitoring period. Although the number of hours using the neuroprosthesis remained constant, subjects shifted their usage to more functional standing versus more maintenance exercise, suggesting that the subjects incorporated the neuroprosthesis into their lives. Safety and reliability of the system were demonstrated by electrode stability and a high component survivability rate (>90%).

Conclusions: This group of 15 subjects is the largest cohort of implanted lower-extremity neuroprosthetic exercise and standing system users. The safety and efficiency data from this group, and acceptance of the neuroprosthesis as demonstrated by continued usage, indicate that future efforts toward commercialization of a similar device may be warranted.

Trial registration: ClinicalTrials.gov NCT00004445.

Copyright © 2012 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

A schematic of the standing neuroprosthesis with photos of both the internal and external components.

Figure 2

The levels of knee extension strength (a) and fatigue resistance (b) that were established from the reconditioning exercise program and standing training with the neuroprosthesis were maintained at the follow-up visit.

Figure 3

Maximum standing times remained relatively constant or decreased slightly when comparing the follow-up value to that at discharge.

Figure 4

Body weight distribution data was collected for seven subjects at follow-up, but only three subjects had paired data at discharge. A trend of decreased body weight supported by the lower extremities was seen, but was not statistically significant from the discharge values.

Figure 5

The majority of both epimysial and intramuscular electrodes were stable over time as supported by small threshold changes (

Figure 6

Kaplan-Meyer estimates of probability of device survival. At 30 months post surgery probability of survival was 93.0% for IRS-8s, 97.1% for IM electrodes, and 90.4% for EP electrodes.