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Wearable exoskeleton for knee rehabilitation with Functional Electrical Stimulation

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Smart exoskeleton improves knee rehabilitation

Knee injuries often take longer to rehabilitate than expected, with disappointing results. BELK has created a wearable solution, usable at home during normal walking and activated only when needed.

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Knee injuries, one of the most common joint problems, can be caused by sports, traffic accidents, brain damage, arthritis and other age-related degenerative diseases. Rehabilitation usually aims to recover the flexion grade of the knee but is stopped once 100 º of flexion is achieved, which doesn’t address gait pattern and natural knee movement. The EU-supported BELK project developed an ‘assisted-as-needed’ exoskeleton to proportionally apply torque only when a patient deviates from the preprogrammed desired movement pattern. The device is based on an algorithm which simultaneously drives the assisted-as-needed programme and a functional electro stimulation (FES) array of electrodes which induce muscle contraction. “This force field control with integrated FES produces a natural gait pattern,” says project coordinator Carlos Fernandez. “The system only helps movement during the part of a stretch where patients cannot do it for themselves, resulting in more intentional and intuitive rehabilitation. No commercial alternatives offer this.”

The single-joint-exoskeleton solution

www.gogoa.eu (Gogoa Mobility Robots), the project host, set out to develop a wearable knee rehabilitation device usable by both physiotherapists and patients themselves, at home or in the street. The resultant solution is comprised of three main components: a robotic exoskeleton, a remote control and a data collector. The lightweight exoskeleton is designed to be easily and quickly adjusted to the patient’s anatomy and can be used in a supine, sitting or gait position. Powered by a lithium battery, lasting up to 4 hours of continuous motion, BELK can generate up to 35 Nm (newton-metre) in the knee joint. The device itself weighs 3 kg and can be used with patients 1.5–1.95 m in height and weighing up to 100 kg. Using Bluetooth technology, the remote control works through an Android application installed on a tablet which comes as part of the package. This displays alarms for issues such as too much force being exerted, alongside the device’s status, such as battery power remaining. The operating modes allow users to control parameters such as speed, torque and range of motion. An algorithm integrates FES capabilities into the exoskeleton which modulates the mechanical resistance exerted on the leg. The data collector displays information provided by the exoskeleton’s strain gauges and the encoder which measures the angle of the joint. These allow the rehab process to be evaluated and the device’s configuration to be adjusted. The BELK system has successfully undergone clinical trials in Cruces and Santiago hospitals. The 20 patients reported comfort with the system and no adverse reactions. Participants’ gait patterns were found to have improved at the end of treatment, with rehabilitation time reduced from 12 to 9 sessions.

Cost-effective and time-saving

“As our solution can be used at home it saves on the cost and time of travel to a rehabilitation centre,” adds Fernandez. “Furthermore, our patented cable transmission system makes production cost-effective, putting it at a similar price to alternatives, but with more advanced functions.” Gogoa is currently waiting for a CE mark for its exoskeleton to be authorised by the medical agency responsible in Spain. Afterwards, the company will introduce it into the European market prior to making submissions to the Food and Drug Administration for the American market.

Keywords

BELK, joint, injury, knee, rehabilitation, exoskeleton, wearable, gait

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