A Unilateral Active Knee Exoskeleton to Assist Individuals with Hemiparesis - a Pilot Study
and Nicola Vitiello
AI summary
Problem
Poststroke hemiparetic gait frequently involves reduced knee flexion during swing and knee hyperextension or buckling during stance, severely limiting mobility and independence. Current orthotic solutions often lack the lightweight design and precise, adaptive torque control needed to effectively address these specific impairments.
Approach
The researchers designed a lightweight, unilateral active knee exoskeleton (AKO-β) featuring a series-elastic actuator and a control system that uses adaptive oscillators to estimate gait phase in real time. This enables the device to deliver precisely timed, phase-locked assistive torque to the impaired knee during walking.
Key results
- Increased paretic knee flexion during swing by 18.70° (+44.9%)
- Reduced knee hyperextension in stance by 4.50°
- Improved overall paretic knee gait variable score by 37.5%
- Validated compact series-elastic actuator design with precise closed-loop torque control
Why it matters
This compact, phase-adaptive exoskeleton demonstrates strong potential for clinical rehabilitation by safely restoring natural knee kinematics and enhancing walking independence in stroke survivors.
Abstract
Most individuals who experience a stroke exhibit sev- eral sensorimotor impairments that limit their independence in everyday activities. Hemiparetic gait is frequently characterized by reduced knee flexion in swing due to knee stiffness or muscle weakness and knee hyperextension or knee buckling in the stance phase. Recently, unilateral-powered orthoses have been designed to overcome the limitations of the passive knee–ankle–foot orthoses. This study presents a unilateral active knee orthosis exoskeleton, AKO-β, endowed with a series-elastic actuator and designed to assist the knee in flexion and extension movements. In this article, we describe the system mechatronic design and its characterization on the bench, the control system, and pilot experiments with three poststroke participants. The device has a weight of 1.78 kg on Received 25 October 2024; revised 26 April 2025 and 8 July 2025; accepted 6 August 2025. Date of publication 16 September 2025; date of current version 29 September 2025. This work was supported in part by European Commission under the CYBERLEGs Plus Plus Project under Grant 731931, within the H2020 framework (H2020-ICT-25-2016-2017), and in part by the Italian Ministry of Research, under the complementary actions to the NRRP “Fit4MedRob - Fit for Medical Robotics” under Grant PNC0000007. This article was recommended for publication by Associate Editor H. Zhao and Editor K. Mombaur upon evaluation of the reviewers’ comments. (Andrea Pergolini and Clara Beatriz Sanz-Morère are co-first authors.) (Corresponding authors: Andrea Pergolini; Nicola Vitiello.) This work involved human subjects or animals in its research. Approval of all ethical and experimental procedures and protocols was granted by the local Ethics Committee of Area Vasta Centro Toscana, Italy, notified to the Italian Ministry of Health, under Application No. 16454_spe, and performed in line with the Declaration of Helsinki. Andrea Pergolini, Chiara Livolsi, Filippo Dell’Agnello, Andrea Baldoni, and Emilio Trigili are with the The BioRobotics Institute, Scuola Supe- riore Sant’Anna, 56127 Pisa, Italy, and also with the Department of Ex- cellence in Robotics and AI, Scuola Superiore Sant’Anna, 56127 Pisa, Italy (e-mail: andrea.pergolini@santannapisa.it; chiara.livolsi@santannapisa.it; emilio.trigili@santannapisa.it). Clara Beatriz Sanz-Morère was with the The BioRobotics Institute, Scuola Superiore Sant’Anna, 56127 Pisa, Italy. She is now with the Center for Automa- tion and Robotics, Spanish National Research Council, 28690 Madrid, Spain (e-mail: clara.sanzmorere@csic.es). Matteo Fantozzi was with the The BioRobotics Institute, Scuola Superiore Sant’Anna, 56127 Pisa, Italy. He is now with the IUVO S.r.l., 56025 Pontedera, Italy (e-mail: matteo.fantozzi@iuvo.company). Tommaso Ciapetti is with the Institute of Recovery and Care of Scientific Character (IRCCS) Fondazione Don Carlo Gnocchi, 50143 Firenze, Italy. Alessandro Maselli was with the IRCCS Fondazione Don Carlo Gnocchi, 50143 Firenze, Italy. He is now with the Dipartimento delle Professioni Tecnico Sanitarie, della Riabilitazione e della Prevenzione Azienda USL Toscana Sudest, 52100 Arezzo, Italy. Simona Crea and Nicola Vitiello are with the The BioRobotics Institute, Scuola Superiore Sant’Anna, 56127 Pisa, Italy, also with the Department of Excellence in Robotics and AI, Scuola Superiore Sant’Anna, 56127 Pisa, Italy, and also with the IRCSS Fondazione Don Carlo Gnocchi, 50143 Firenze, Italy (e-mail: simona.crea@santannapisa.it; nicola.vitiello@santannapisa.it). This article has supplementary downloadable material available at https://doi. org/10.1109/TRO.2025.3610187, provided by the authors. Digital Object Identifier 10.1109/TRO.2025.3610187 the user’s leg, with a lateral encumbrance of 76 mm. The pilot experiments aimed to verify the effects of the exoskeleton assis- tance in hemiparetic gait patterns. When walking with the device, participants on average increased the knee flexion on the paretic side by 18.70° (+44.9%) during swing and decreased knee hyperex- tension in stance by 4.50°, compared to walking without it. Overall, when walking with the exoskeleton, subjects showed an improved gait variable score of the paretic knee profile by 37.5% compared to walking without it. The temporal and spatial gait symmetry indices did not show clear changes, although an improvement in symmetry was observed in two of the three participants. These preliminary results suggest the potential benefits of the unilateral active knee orthosis exoskeleton to enhance and restore mobility in individuals with hemiparetic gait.