Adaptive control ankle robotics training durably improves gait biomechanics in chronic hemiparetic stroke and footdrop

TL;DR

A wearable ankle robot improved walking for stroke survivors with foot drop, with benefits lasting two months after training.

Contribution

A wearable ankle exoskeleton with adaptive control improved gait biomechanics and functional mobility in chronic stroke patients.

Findings

AMBLE training improved gait biomechanics like toe clearance and ankle dorsiflexion angular velocity.

Functional outcomes such as walking speed and 6-minute walk distance improved after training.

Most biomechanical improvements were retained two months after training ended.

Abstract

Robotics has emerged as a promising avenue for gait rehabilitation after stroke. We developed a wearable ankle exoskeleton (AMBLE) for dorsiflexion assist-as-needed training with adaptive control timing to individualize assistance across gait cycle sub-events. This single-armed, non-controlled study investigates effects of 9 weeks x 2 sessions/week robotics training on walking function in persons with chronic stroke and foot drop, and durability 2 months after training ends.

Subjects included N = 24 participants (12 male, 12 female) age 57 ± 13 years with mean 10 ± 9 years since stroke. All baseline and post-training outcomes included optical motion capture for 3-D gait biomechanics and were conducted during unassisted (no robot) over-ground walking conditions. AMBLE training improved select gait biomechanics outcomes including maximum toe clearance (mm, pre- 69±28 versus post- 79±30, p < 0.01), ankle peak dorsiflexion angular velocity (°/s, 35±32 versus 47±40, p < 0.01), heel-first foot strikes (%steps, 31±41 versus 44±43, p < 0.01), and paretic step length (cm, 37±16 versus 40±14, p < 0.01. Functional outcomes that improved with training included 10-meter self-selected (m/s, 0.66±0.24 versus 0.70±0.23, p < 0.01) and fastest comfortable velocities (m/s, 0.80±0.31 versus 0.86±0.30, p < 0.01), Dynamic Gait Index (points, 14±5 versus 17±3, p < 0.01), 6-minute walk distance (m, 252±106 versus 280±109, p < 0.01), and Stroke Impact Scale-Mobility (0-100, 280±109 versus 88±10, p < 0.01); all achieving minimal clinically important differences, except walking velocities. Durability testing 2 months after cessation of robotics training showed retention of most biomechanical improvements, including maximum toe clearance (mm, 78.4±26.1, p < 0.01), dorsiflexion angular velocity (°/s, 42.5±37.5, p < 0.01), and heel-first foot strikes (%steps, 46±43, p < 0.01), and most functional outcomes. Notably, durability testing revealed emergence of two new kinematic improvements: increased knee flexion (deg, 33.1±16.5 versus 36.9±17.7, p < 0.01) and hip flexion (deg, 36.8±9.5 versus 39.6±9.2, p < 0.05), while hip abduction and hip hike do not change.

Nine hours of AMBLE ankle robotics training across 9 weeks durably improves gait biomechanics and functional mobility for persons with chronic stroke and foot drop, even decades post-stroke. Further studies are needed to investigate precision adaptive control robotics for stroke and other mobility disability conditions.

Trial registration: Clinical trial identifier: NCT04594837.

Figures