Robot-mediated overground gait training for transfemoral amputees with a powered bilateral hip orthosis: a pilot study

Abstract

Background: Transfemoral amputation is a serious intervention that alters the locomotion pattern, leading to secondary disorders and reduced quality of life. The outcomes of current gait rehabilitation for TFAs seem to be highly dependent on factors such as the duration and intensity of the treatment and the age or etiology of the patient. Although the use of robotic assistance for prosthetic gait rehabilitation has been limited, robotic technologies have demonstrated positive rehabilitative effects for other mobility disorders and may thus offer a promising solution for the restoration of healthy gait in TFAs. This study therefore explored the feasibility of using a bilateral powered hip orthosis (APO) to train the gait of community-ambulating TFAs and the effects on their walking abilities.

Methods: Seven participants (46-71 years old with different mobility levels) were included in the study and assigned to one of two groups (namely Symmetry and Speed groups) according to their prosthesis type, mobility level, and prior experience with the exoskeleton. Each participant engaged in a maximum of 12 sessions, divided into one Enrollment session, one Tuning session, two Assessment sessions (conducted before and after the training program), and eight Training sessions, each consisting of 20 minutes of robotically assisted overground walking combined with additional tasks. The two groups were assisted by different torque-phase profiles, aiming at improving symmetry for the Symmetry group and at maximizing the net power transferred by the APO for the Speed group. During the Assessment sessions, participants performed two 6-min walking tests (6mWTs), one with (Exo) and one without (NoExo) the exoskeleton, at either maximal (Symmetry group) or self-selected (Speed group) speed. Spatio-temporal gait parameters were recorded by commercial measurement equipment as well as by the APO sensors, and metabolic efficiency was estimated via the Cost of Transport (CoT). Additionally, kinetic and kinematic data were recorded before and after treatment in the NoExo condition.

Results: The one-month training protocol was found to be a feasible strategy to train TFAs, as all participants smoothly completed the clinical protocol with no relevant mechanical failures of the APO. The walking performance of participants improved after the training. During the 6mWT in NoExo, participants in the Symmetry and Speed groups respectively walked 17.4% and 11.7% farther and increased walking speed by 13.7% and 17.9%, with improved temporal and spatial symmetry for the former group and decreased energetic expenditure for the latter. Gait analysis showed that ankle power, step width, and hip kinematics were modified towards healthy reference levels in both groups. In the Exo condition metabolic efficiency was reduced by 3% for the Symmetry group and more than 20% for the Speed group.

Conclusions: This study presents the first pilot study to apply a wearable robotic orthosis (APO) to assist TFAs in an overground gait rehabilitation program. The proposed APO-assisted training program was demonstrated as a feasible strategy to train TFAs in a rehabilitation setting. Subjects improved their walking abilities, although further studies are required to evaluate the effectiveness of the APO compared to other gait interventions. Future protocols will include a lighter version of the APO along with optimized assistive strategies.

Keywords: Exoskeleton; Gait rehabilitation; Gait training; Hip orthosis; Overground walking; Transfemoral amputees.

Fig. 1

A. Experimental protocol: the Enrollment session including initial evaluations and GA without the APO (NoExo) was followed by a Tuning session to select the assistive parameters. Participants then performed a Pre-training Assessment session (PreTA) with two 6mWTs in NoExo and with the APO (Exo) and eight Training sessions in Exo. Last, the Post-training Assessment (PostTA) was identical to the PreTA with a final GA. B. Tuning procedure for two representative participants of the Symmetry (ID2) and Speed (ID4) groups. For the Symmetry group, Step #0 aimed at identifying hip angle abnormalities by comparing hip kinematics with the physiological range (grey area). Then, in Step #1, data from the GA—where the 0% of the gait phase corresponded to heel strike (HS)– were shifted to reset the phase at the hip flexion peak (HFP). Draft assistive torque profiles were designed (dashed lines) to improve temporal symmetry: on the sound side, the flexion peak (black circle) was delivered earlier than the physiological one to promote an earlier flexion and reduce stance time; on the prosthetic side, the extension peak (grey square) was delayed with respect to the physiological pattern to promote a longer stance. During Step #2, each participant walked in TM and AM with the initial torque profiles (colored dashed lines); amplitude was gradually increased based on the participant’s preference and phase and duration were fine-tuned. At the end of the session, the final torque profiles (solid bold colored lines) were locked. For the Speed group, the Tuning procedure started from Step #1 and the draft torque profiles were designed to maximize the net power transferred to the participant: peak torque phases were synchronous to flexion/extension velocity peaks and torque durations corresponded to flexion/extension durations. Step #2 and Step #3 followed the same procedure as for the Symmetry group

Fig. 2

Picture of one of the participants who completed the clinical protocol and example of hip angular profiles, APO output torque and power measured by the onboard sensors for three representative participants during the 6mWT of the PostTA session (ID2, ID4 and ID7). Data are shown as median (IQR) for the Sound and Prosthetic sides

Fig. 3

Barplots of the most relevant measurements obtained during the 6mWT. Data are reported individually on the left as median (IQR) and grouped on the right as median (min, max). All results are shown for NoExo and Exo conditions during PreTA and PostTA. The differences between the medians of each condition are shown in %

Fig. 4

Relevant results during the Gait Analysis (GA). A. Ankle power for each participant as a function of the gait phase on the prosthetic and sound sides. Dotted and solid lines represent respectively data from PreTA and PostTA. B. Barplot of the step width. Data are reported individually on the left as mean ± SD and grouped on the right as median, (min, max). All results are shown for PreTA and PostTA in NoExo. The differences between the medians of each condition are shown in %