A muscle-driven approach to restore stepping with an exoskeleton for individuals with paraplegia

Abstract

BackgroundFunctional neuromuscular stimulation, lower limb orthosis, powered lower limb exoskeleton, and hybrid neuroprosthesis (HNP) technologies can restore stepping in individuals with paraplegia due to spinal cord injury (SCI). However, a self-contained muscle-driven controllable exoskeleton approach based on an implanted neural stimulator to restore walking has not been previously demonstrated, which could potentially result in system use outside the laboratory and viable for long term use or clinical testing. In this work, we designed and evaluated an untethered muscle-driven controllable exoskeleton to restore stepping in three individuals with paralysis from SCI.MethodsThe self-contained HNP combined neural stimulation to activate the paralyzed muscles and generate joint torques for limb movements with a controllable lower limb exoskeleton to stabilize and support the user. An onboard controller processed exoskeleton sensor signals, determined appropriate exoskeletal constraints and stimulation commands for a finite state machine (FSM), and transmitted data over Bluetooth to an off-board computer for real-time monitoring and data recording. The FSM coordinated stimulation and exoskeletal constraints to enable functions, selected with a wireless finger switch user interface, for standing up, standing, stepping, or sitting down. In the stepping function, the FSM used a sensor-based gait event detector to determine transitions between gait phases of double stance, early swing, late swing, and weight acceptance.ResultsThe HNP restored stepping in three individuals with motor complete paralysis due to SCI. The controller appropriately coordinated stimulation and exoskeletal constraints using the sensor-based FSM for subjects with different stimulation systems. The average range of motion at hip and knee joints during walking were 8.5°–20.8° and 14.0°–43.6°, respectively. Walking speeds varied from 0.03 to 0.06 m/s, and cadences from 10 to 20 steps/min.ConclusionsA self-contained muscle-driven exoskeleton was a feasible intervention to restore stepping in individuals with paraplegia due to SCI. The untethered hybrid system was capable of adjusting to different individuals’ needs to appropriately coordinate exoskeletal constraints with muscle activation using a sensor-driven FSM for stepping. Further improvements for out-of-the-laboratory use should include implantation of plantar flexor muscles to improve walking speed and power assist as needed at the hips and knees to maintain walking as muscles fatigue.

Effect of exoskeletal joint constraint and passive resistance on metabolic energy expenditure: Implications for walking in paraplegia

“…The exoskeletal component of the HNP, rather than a commercially-available exoskeleton, was selected for this study because its design is compatible with implanted neuroprostheses that individuals with paraplegia would use for stepping [ 1 , 2 , 27 ]. While the results from this study are mostly applicable to this specific exoskeleton [ 6 , 15 , 16 , 17 , 28 ], the results are also valuable to any hybrid neuroprosthesis exoskeleton design where the primary power for walking is derived from neuromuscular stimulation of paralyzed muscles (i.e. a muscle-first approach) and where exoskeleton constraints, weight, and joints’ passive resistance could place considerable metabolic demand on the user and affect their potential for restoring community level ambulation.…”

Hybrid Neuroprosthesis for Lower Limbs

“…The same research group built a muscle-driven controllable exoskeleton to restore walking, sitting, and standing to people with SCI [38]. They combined the mechanics used in [36] and adaptations to the hip control described in [37].…”

Hybrid FES–robotic gait rehabilitation technologies: a review on mechanical design, actuation, and control strategies

“…A similar solution to manage muscle fatigue and joint trajectory was introduced by Chang et al (2016Chang et al ( , 2017. The Stimulation-driven exoskeleton system was designed to restore the loss of motor function caused by varying types of paralysis from spinal cord trauma.…”

“…3 Overview of the Self-contained exoskeleton. Retrieved from (Chang et al 2017) The robotic orthosis employed is known as Gravity Balanced Orthosis (GBO). GBO is a treadmill-based device which allows intension based ambulation of the patient and optimizes the effects of gravity on their limbs (Fig.…”