Modares Mechanical Engineering

Modares Mechanical Engineering

Design, Control, and Experimental Evaluation of a Lightweight Active Knee–Ankle–Foot Orthosis with Adjustable Knee Motion for Mobility Assistance After Spinal Cord Injury

Document Type : Original Article

Authors
Sahand Hosseinpour Malakouti
Sadjaad Ozgoli
Electrical and Computer Engineering Department, Tarbiat Modares University, Tehran, Iran
10.48311/mme.2026.118299.82908
Abstract
For individuals with spinal cord injury (SCI) who walk with conventional knee–ankle–foot orthoses (KAFOs), locked knees and compensatory trunk and upper-limb motions can limit gait efficiency. This study presents a lightweight active KAFO that provides powered knee assistance while still being used like a conventional KAFO. The device integrates a backdrivable knee actuator within a two-level control architecture: a high-level controller, comprising a finite state machine and a parametric trajectory generator that computes the knee reference from user-selected step height and speed, and a low-level position-based impedance controller tracks this trajectory. Step height and speed can be adjusted in real time via an on-board touchscreen interface, and a ramp-based timing strategy allows smooth changes in gait cycle duration over roughly a two-fold range. A pilot case study was conducted on a single adult with chronic incomplete SCI who walks with KAFOs and a walker. Two configurations were compared: his usual conventional KAFO set-up and one with the proposed active KAFO. Clinical outcome measures included the 10m walking test (10MWT), the 6 min walking test (6MWT) and end-of-test heart rate. With the active KAFO, the participant achieved a higher 10MWT walking speed than with his conventional KAFOs, whereas no clear difference was observed in 6MWT distance and heart rate responses remained in a similar range. These preliminary results suggest that an active KAFO with an adjustable knee trajectory and on-board tuning of gait parameters may offer a feasible intermediate option between conventional KAFOs and full lower-limb exoskeletons.
Keywords
Spinal cord injury
Powered knee exoskeleton
knee&‌ndash
ankle&‌ndash
foot orthosis
Rehabilitation robotics
Clinical case study

Subjects

[1]            N. Sezer, S. Akkuş, and F. G. Uğurlu, "Chronic complications of spinal cord injury," World journal of orthopedics, vol. 6, no. 1, p. 24, 2015, doi: 10.5312/wjo.v6.i1.24.
[2]            N. S. C. I. S. Center, "Facts and Figures at a Glance," Birmingham, AL: University of Alabama at Birmingham, vol. 10, 2016. [Online]. Available: https://www.scirepair.com/uploads/8/6/1/5/86150236/spinal_cord_injury_facts_and_figures_at_a_glance_2017.pdf.
[3]            R. A. Auberger, "Functional Compensation of Gait Deficits with Minimal Actuation," ETH Zurich, 2021. [Online]. Available: https://www.research-collection.ethz.ch/server/api/core/bitstreams/7e7aecd0-a74f-4a27-a94c-73ec97a32683/content
[4]            T. Yakimovich, E. D. Lemaire, and J. Kofman, "Engineering design review of stance-control knee-ankle-foot orthoses," Journal of Rehabilitation Research & Development, vol. 46, no. 2, 2009, doi: 10.1682/JRRD.2008.02.0024.
[5]            K. Ghoseiri and A. Zucker-Levin, "Long-term locked knee ankle foot orthosis use: A perspective overview of iatrogenic biomechanical and physiological perils," Frontiers in Rehabilitation Sciences, vol. 4, p. 1138792, 2023, doi: doi.org/10.3389/fresc.2023.1138792.
[6]            M. J. Escalona et al., "Cardiorespiratory demand and rate of perceived exertion during overground walking with a robotic exoskeleton in long-term manual wheelchair users with chronic spinal cord injury: A cross-sectional study," Annals of physical and rehabilitation medicine, vol. 61, no. 4, pp. 215-223, 2018, doi: 10.1016/j.rehab.2017.12.008.
[7]            J. Kressler, T. Wymer, and A. Domingo, "Respiratory, cardiovascular and metabolic responses during different modes of overground bionic ambulation in persons with motor-incomplete spinal cord injury: A case series," Journal of Rehabilitation Medicine (Stiftelsen Rehabiliteringsinformation), vol. 50, no. 2, 2018, doi: 10.2340/16501977-2281.
[8]            A. Plaza, M. Hernandez, G. Puyuelo, E. Garces, and E. Garcia, "Wearable rehabilitation exoskeletons of the lower limb: analysis of versatility and adaptability," Disability and Rehabilitation: Assistive Technology, vol. 18, no. 4, pp. 392-406, 2023, doi: 10.1080/17483107.2020.1858976.
[9]            D. Herrera-Valenzuela et al., "A qualitative study to elicit user requirements for lower limb wearable exoskeletons for gait rehabilitation in spinal cord injury," Journal of NeuroEngineering and Rehabilitation, vol. 20, no. 1, p. 138, 2023, doi: 10.1186/s12984-023-01264-y.
[10]          M. Laffranchi et al., "User-Centered design and development of the modular TWIN lower limb exoskeleton," Frontiers in neurorobotics, vol. 15, p. 709731, 2021, doi: 10.3389/fnbot.2021.709731.
[11]          S. H. Kwon et al., "Energy efficiency and patient satisfaction of gait with knee-ankle-foot orthosis and robot (ReWalk)-assisted gait in patients with spinal cord injury," Annals of rehabilitation medicine, vol. 44, no. 2, pp. 131-141, 2020, doi: 10.5535/arm.2020.44.2.131.
[12]          A. Rodríguez‑Fernández, J. Lobo‑Prat, R. Tarragó, D. Chaverri, X. Iglesias, and L. Guirao‑Cano, "Comparing walking with knee‑ankle‑foot orthoses and a knee‑powered exoskeleton after spinal cord injury: a randomized, crossover clinical trial.," Scientific reports, vol. 12, 2022, doi: 10.1038/s41598-022-23556-4.
[13]          M. Arazpour, A. Chitsazan, M. A. Bani, G. Rouhi, F. T. Ghomshe, and S. W. Hutchins, "The effect of a knee ankle foot orthosis incorporating an active knee mechanism on gait of a person with poliomyelitis," Prosthetics and orthotics international, vol. 37, no. 5, pp. 411-414, 2013, doi: 10.1177/0309364612469140.
[14]          G. S. Sawicki and D. P. Ferris, "A pneumatically powered knee-ankle-foot orthosis (KAFO) with myoelectric activation and inhibition," Journal of neuroengineering and rehabilitation, vol. 6, no. 1, p. 23, 2009, doi: 10.1186/1743-0003-6-23.
[15]          G. Puyuelo-Quintana et al., "A new lower limb portable exoskeleton for gait assistance in neurological patients: a proof of concept study," Journal of NeuroEngineering and Rehabilitation, vol. 17, no. 1, p. 60, 2020, doi: 10.1186/s12984-020-00690-6.
[16]          M. S. Ashrafi, M. Nazari, N. Sepehry, M. Mahdizadeh Rokhi, P. Samimi, and M. Attarchi, "Design and implementation of a fuzzy output feedback assistive controller for a series-elastic-actuator-driven knee exoskeleton," Modares Mechanical Engineering, vol. 22, no. 8, pp. 541-553, 2022, doi: 10.52547/mme.22.8.541.
[17]          J. de Miguel Fernandez et al., "Adapted assistance and resistance training with a knee exoskeleton after stroke," IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 31, pp. 3265-3274, 2023, doi: 10.1109/TNSRE.2023.3303777.
[18]          C. Meijneke et al., "Symbitron exoskeleton: Design, control, and evaluation of a modular exoskeleton for incomplete and complete spinal cord injured individuals," IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 29, pp. 330-339, 2021, doi: 10.1109/TNSRE.2021.3049960.
[19]          C. Nesler, G. Thomas, N. Divekar, E. J. Rouse, and R. D. Gregg, "Enhancing voluntary motion with modular, backdrivable, powered hip and knee orthoses," IEEE robotics and automation letters, vol. 7, no. 3, pp. 6155-6162, 2022, doi: 10.1109/LRA.2022.3145580.
[20]          J. Kazemi and S. OZGOLI, "Parametric model of human constrained gait with implementation on exoped exoskeleton," Modares Mechanical Engineering, vol. 18, no. 6, pp. 12-18, 2018. [Online]. Available: https://mme.modares.ac.ir/article_10442_890ff058169b5a1d1a7f07d467f1f57b.pdf.
[21]          J. M. Font-Llagunes, U. Lugrís, D. Clos, F. J. Alonso, and J. Cuadrado, "Design, control, and pilot study of a lightweight and modular robotic exoskeleton for walking assistance after spinal cord injury," journal of Mechanisms and Robotics, vol. 12, no. 3, p. 031008, 2020, doi: 10.1115/1.4045510.
[22]          D. García-Vallejo, J. M. Font-Llagunes, and W. Schiehlen, "Dynamical analysis and design of active orthoses for spinal cord injured subjects by aesthetic and energetic optimization," Nonlinear dynamics, vol. 84, no. 2, pp. 559-581, 2016, doi: 10.1007/s11071-015-2507-1.
[23]          M. Febrer-Nafría, B. J. Fregly, and J. M. Font-Llagunes, "Evaluation of optimal control approaches for predicting active knee-ankle-foot-orthosis motion for individuals with spinal cord injury," Frontiers in Neurorobotics, vol. 15, p. 748148, 2022, doi: 10.3389/fnbot.2021.748148.
[24]          "Cubemars, “AK80-8 KV60 robotic actuator,” Cubemars,." [Online]. Available: https://www.cubemars.com/product/ak80-8-kv60-robotic-actuator.html.
 
Modares Mechanical Engineering
Volume 26, Issue 4
March 2026
Pages 261-269