Ankle dorsiflexion assistance of patients with foot drop using a powered ankle-foot orthosis to improve the gait asymmetry

Of all the foot drop assistance out there which one is your doctor using to get you 100% recovered in walking?  

• ankle–foot rehabilitation system (1 post to May 2016)

• ankle–foot rehabilitation (1 post to October 2023)

• ankle–foot orthoses (1 post to October 2022)

• ankle exoskeleton (1 post to May 2022)

• ankle activation (1 post to May 2020)

Ankle dorsiflexion assistance of patients with foot drop using a powered ankle-foot orthosis to improve the gait asymmetry

• Wonseok Shin,
• Dongwoo Nam,
• Bummo Ahn,
• Sangjoon J. Kim,
• Dong Yeon Lee,
• Suncheol Kwon &
• Jung Kim 

Journal of NeuroEngineering and Rehabilitation volume 20, Article number: 140 (2023) Cite this article

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Abstract

Background

Foot drop is a neuromuscular disorder that causes abnormal gait patterns. This study developed a pneumatically powered ankle-foot orthosis (AFO) to improve the gait patterns of patients with foot drop. We hypothesized that providing unilateral ankle dorsiflexion assistance during the swing phase would improve the kinematics and spatiotemporal gait parameters of such patients. Accordingly, this study aims to examine the efficacy of the proposed assistance system using a strategy for joint kinematics and spatiotemporal gait parameters (stride length, swing velocity, and stance phase ratio). The analysis results are expected to provide knowledge for better design and control of AFOs in patients with foot drop.

Method

Ten foot drop patients with hemiparesis (54.8 y ± 14.1 y) were fitted with a custom AFO with an adjustable calf brace and portable air compressor for ankle dorsiflexion assistance in the gait cycle during the swing phase. All subjects walked under two different conditions without extensive practice: (1) barefoot and (2) wearing a powered AFO. Under each condition, the patients walked back and forth on a 9-m track with ten laps of level ground under the supervision of licensed physical therapists. The lower-limb joint and trunk kinematics were acquired using 12 motion-capture cameras.

Results

We found that kinematic asymmetry decreased in the three lower-limb joints after ankle dorsiflexion assistance during the swing phase. The average ankle-joint angle increased after using the AFO during the entire gait cycle. Similarly, the knee-joint angle showed a slight increase while using the AFO, leading to a significantly decreased standard deviation within patients. Conversely, the hip-joint angle showed no significant improvements with assistance. While several patients exhibited noticeably lower levels of asymmetry, no significant changes were observed in the average asymmetry of the swing velocity difference between the affected and unaffected sides while using the AFO.

Conclusion

We experimentally validated that ankle dorsiflexion assistance during the swing phase temporarily improves gait asymmetry in foot-drop patients. The experimental results also prove the efficacy of the developed AFO for gait assistance in foot-drop patients.

Introduction

Foot drop is a common symptom of brain or spinal cord disorders such as stroke, multiple sclerosis, and cerebral palsy [1]. These diseases typically lead to weaknesses or spasticity in the ankle dorsiflexor muscles that hinder the normal gait pattern. Accordingly, patients with foot drop experience two primary challenges: foot slap during the loading response and toe drag during the swing phase [2]. To compensate for these challenges, patients generally exhibit compensatory behaviors such as hip hiking and circumduction [3, 4].

Ankle-foot orthosis (AFO) has been used as a representative solution to improve gait quality by decreasing the ankle kinematic asymmetry in patients with foot drop [5, 6]. A leaf-spring-based AFO was developed to restrict ankle dorsiflexion by providing plantar flexion torque through a passive spring component [7, 8]. Several studies have reported that passive AFOs have a trade-off between the range of motion and power capacity of the system, depending on passive stiffness [9,10,11]. Blaya et al. [12] discovered that modulating the mechanical impedance of the AFO prevented slap foot occurrence and improved kinematic abnormalities, compared to zero- or constant-joint impedance modes. Shorter et al. [13] evaluated the kinematic efficacy of ankle dorsiflexion assistance using a portable AFO. Awad et al. [14] provided bidirectional assistance for both dorsiflexion (DF) and plantarflexion (PF) targeting patients with hemiplegic walking. Previous AFOs share similar designs and control schemes [15].

Adding mass to the legs, particularly directly to the ankle, impedes natural gait and hinders leg kinematics [16,17,18]. The Harvard exosuit that uses cable-based power transmission is the most representative example of a remote actuation system applied to assist patients with abnormal gait [19, 20] by minimizing the added mass to the ankle joint. The mass added to the ankle joint was sufficiently small (~ 0.5 kg) to avoid impeding the natural gait, resulting in a metabolic penalty. Pneumatic transmission is another example of remote force transmission [21,22,23,24,25,26,27]. A pneumatic-based wearable robot generally consists of a compressor as an energy source and a pneumatic actuator, connected through the air tube.

In our previous study, we developed an untethered AFO powered by a fully portable pneumatic compressor for foot drop correction [26, 27]. The custom portable compressor enabled a fully untethered system for patients with foot drop, which was impossible with most commercially available pneumatic pumps with excessive size and weight [26] based on a simple on-off valve controller. We evaluated the immediate efficacy of the developed pneumatic AFO for foot drop correction by identifying improvements in ankle angle on the affected side and the degree of asymmetry of both the affected and unaffected ankle angles [27]. However, there is limited information available regarding the kinematics of other lower limb joints and spatiotemporal gait asymmetry parameters after ankle dorsiflexion assistance during the swing phase of patients with foot drop using untethered fully portable pneumatic-powered AFOs (FP-PPAFOs).

This study aimed to investigate the effect of ankle dorsiflexion assistance on gait parameters in patients with foot drop. We hypothesized that ankle dorsiflexion assistance improves both kinematic and spatiotemporal gait asymmetries. For long-term deployment and high transmissibility of the pneumatic power from the AFO to the affected ankle, we improved both energy source modules with the AFO design. The hypothesis was validated by analyzing kinematic and spatiotemporal data from motion analysis.

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