The Actuation System of the Ankle Exoskeleton T-FLEX: First Use Experimental Validation in People with Stroke

Abstract

Robotic devices can provide physical assistance to people who have suffered neurological impairments such as stroke. Neurological disorders related to this condition induce abnormal gait patterns, which impede the independence to execute different Activities of Daily Living (ADLs). From the fundamental role of the ankle in walking, Powered Ankle-Foot Orthoses (PAFOs) have been developed to enhance the users' gait patterns, and hence their quality of life. Ten patients who suffered a stroke used the actuation system of the T-FLEX exoskeleton triggered by an inertial sensor on the foot tip. The VICONmotion capture system recorded the users' kinematics for unassisted and assisted gait modalities. Biomechanical analysis and usability assessment measured the performance of the system actuation for the participants in overground walking. The biomechanical assessment exhibited changes in the lower joints' range of motion for 70% of the subjects. Moreover, the ankle kinematics showed a correlation with the variation of other movements analyzed. This variation had positive effects on 70% of the participants in at least one joint. The Gait Deviation Index (GDI) presented significant changes for 30% of the paretic limbs and 40% of the non-paretic, where the tendency was to decrease. The spatiotemporal parameters did not show significant variations between modalities, although users' cadence had a decrease of 70% of the volunteers. Lastly, the satisfaction with the device was positive, the comfort being the most user-selected aspect. This article presents the assessment of the T-FLEX actuation system in people who suffered a stroke. Biomechanical results show improvement in the ankle kinematics and variations in the other joints. In general terms, GDI does not exhibit significant increases, and the Movement Analysis Profile (MAP) registers alterations for the assisted gait with the device. Future works should focus on assessing the full T-FLEX orthosis in a larger sample of patients, including a stage of training.

Keywords: Gait Deviation Index (GDI); Gait Profile Score (GPS); Movement Analysis Profile (MAP); Powered Ankle-Foot Orthosis (PAFO); ankle exoskeleton; biomechanical analysis; overground gait.

Figure 1

T-FLEX’s actuation system states for gait assistance. The red arrows indicate the actuator direction of rotation to assist (A) stance phase, (B) propulsion during toe-off, (C) and foot clearance in swing and heel strike phases. The segmented and continuous lines refer to the transmission elements’ participation in each movement, i.e., in plantarflexion, only the posterior element works, and in dorsiflexion only the frontal element is transmitted.

Figure 2

The actuation system of the T-FLEX exoskeleton that was implemented on the passive orthotic structure. The insole of the left part is added to the non-paretic limb to compensate for the effect due to the device’s use.

Figure 3

Biomechanical setup model used in the study for each participant based on the plug-in gait marker model. The red points on the patient represent the markers and the biological landmarks for the VICON acquisition system. This model involves markers in the Right and Left Posterior Iliac Spines (RPSI and LPSI), Right and Left Anterior Superior Iliac Spines (LASI and RASI), Right and Left Thighs (RTHI and LTHI), Right and Left Knees (RKNE and LKNE), Right and Left Tibias (RTIB and LTIB), Right and Left Ankles (RANK and LANK), Right and Left Toes (RTOE and LTOE), and Right and Left Heels (RHEE and LHEE).

Figure 4

Volunteers’ ankle kinematics during the gait cycle. Numbers on the left part represent the assessed participants. The green curve indicates the assisted gait condition. On the other hand, the blue curve refers to the natural gait pattern (i.e., baseline condition). The gray curve shows a healthy gait pattern obtained from a database of people with no pathological gait available in Figshare at a public repository (https://doi.org/10.6084/m9.figshare.12576965.v1 (accessed on 27 June 2020)). Finally, the vertical lines describe the Toe-Off event (TO) for each of these conditions.

Figure 5

Effect of T-FLEX scenario on the joints’ range of motion. Positive changes (green bar) refer to variations that approach the value of a healthy pattern. Negative changes (red bar) comprehend joints where the ROM departs from the normal gait. Undetermined conditions (yellow bar) integrate magnitudes that exhibit variation, but they do not generate an improvement or an impairment. Lastly, no change states (gray bar) include percentages of less than 10%.

Figure 6

Movement analysis profile. Each column represents one of the kinematic variables such as P-A (Pelvis Anterior-posterior), H-F (Hip Flexion-extension), K-F (Knee Flexion-extension), A-F (Ankle dorsi-plantarflexion), P-U (Pelvic Up-down), H-A (Hip Abduction-Adduction), P-R (Pelvic Rotation), F-R (Foot Rotation), and GPS (Gait Profile Score). The height of the bar indicates the median and IQR RMS value during the trial. The gray columns at the bottom denote the mean values for a healthy gait pattern obtained from [29]. Those values are used as the reference to compare the unassisted condition (blue bars) and assisted gait (green columns).

Figure 7

Results of the usability assessment through the Quebec User Evaluation of Satisfaction with assistive Technology (QUEST) test. The percentage of each topic refers to the number of participants who considered that characteristic as relevant.