A Robotic Exoskeleton for Treatment of Crouch Gait in Children With Cerebral Palsy: Design and Initial Application

Abstract

Crouch gait, a pathological pattern of walking characterized by excessive knee flexion, is one of the most common gait disorders observed in children with cerebral palsy (CP). Effective treatment of crouch during childhood is critical to maintain mobility into adulthood, yet current interventions do not adequately alleviate crouch in most individuals. Powered exoskeletons provide an untapped opportunity for intervention. The multiple contributors to crouch, including spasticity, contracture, muscle weakness, and poor motor control make design and control of such devices challenging in this population. To our knowledge, no evidence exists regarding the feasibility or efficacy of utilizing motorized assistance to alleviate knee flexion in crouch gait. Here, we present the design of and first results from a powered exoskeleton for extension assistance as a treatment for crouch gait in children with CP. Our exoskeleton, based on the architecture of a knee-ankle-foot orthosis, is lightweight (3.2 kg) and modular. On board sensors enable knee extension assistance to be provided during distinct phases of the gait cycle. We tested our device on one six-year-old male participant with spastic diplegia from CP. Our results show that the powered exoskeleton improved knee extension during stance by 18.1° while total knee range of motion improved 21.0°. Importantly, we observed no significant decrease in knee extensor muscle activity, indicating the user did not rely solely on the exoskeleton to extend the limb. These results establish the initial feasibility of robotic exoskeletons for treatment of crouch and provide impetus for continued investigation of these devices with the aim of deployment for long term gait training in this population.

Fig. 1.

Photograph and schematic of the robotic exoskeleton for knee extension assist to alleviate crouch gait from cerebral palsy.

Fig. 2.

Diagram of the FSM used to specify the desired knee extensor assistance at different phases across the gait cycle. The states included stance, early swing, and late swing. The stance state was identified by a reading from the foot sensor greater than 60% of the value measured during quiet standing. The early swing state was identified by a foot sensor reading less than 60% of the value measured during quiet standing and/or if the knee angle surpassed full extension while the foot sensor remained below the threshold (indicating swing). The late swing state was identified by a positive angular velocity of the exoskeleton knee joint (extension) when the knee was flexed greater than 30 degrees.

Fig. 3.

Diagram of the assistance (blue) provided by the exoskeleton relative to different phases of the gait cycle. The motor controller operated in a free (frictionless) state during the early-swing phase to allow for natural knee flexion required for toe-clearance during swing.

Fig. 4.

Mean exoskeleton angular compliance, computed as the difference between the knee joint angle measured from the exoskeleton and the knee joint angle measured from the biological segments during the powered assistance condition. The shaded regions represent ±1SD from the mean.

Fig. 5.

Top Row) Mean knee extensor torques across the gait cycle. Bottom Rows) Mean sagittal plane hip, knee, and ankle joint angles across the gait cycle during the baseline condition (black-dashed), the free knee condition (red), and the powered exoskeleton (blue) conditions. The shaded regions represent ±1SD from the mean. * Indicates significant difference between the respective exoskeleton condition and baseline (p<0.05).

Fig. 6.

Mean EMG linear envelopes (in mV) across the gait cycle during the free knee (red) and powered exoskeleton (blue) conditions. The shaded regions represent ±1SD from the mean.