Human Trials Approved For An Implantable Device That Restores Movement In The Partially Paralyzed

By Beryl Hatton

Three years after suffering a stroke, a 70-year-old man could walk only 10 meters before fatiguing, even with the assistance of a cane and knee and ankle braces. This patient struggled to walk because his stroke caused partial paralysis and prevented him from lifting his unresponsive leg, a condition called foot drop.

Over a million new cases of stroke occur each year worldwide, with approximately 30 percent of patients developing foot drop. Making steps to improve mobility in patients with partial paralysis is Andy Hoffer, a kinesiology professor at Simon Fraser University (SFU) in British Columbia, Canada.

Hoffer and his research team have invented a fully implantable device called Neurostep that restores movement in paralyzed legs. And after 30 years of research and technological innovations that led to the creation of Neurostep, it has been approved for human trials, which began in December, 2007.

With approval from regulatory agencies in Canada and the United Kingdom, a multi-center clinical trial is now moving forward. The trial is coordinated by Victhom Human Bionics, Inc. of Quebec, which purchased Hoffer's SFU spin-off company Neurostream Technologies, the original developer of the Neurostep prototype.

This trial follows on the heels of a preliminary study that tested a Neurostep implant in a human patient. Six months after the Neurostep device was implanted into the unresponsive leg of the 70-year-old stroke patient, he was able to walk 250 meters without tiring and with greater independence. The patient's atrophied muscles strengthened, his gait improved, and he no longer depended on uncomfortable braces for stability and support.

According to Hoffer, the Neurostep is the first fully implantable device that senses signals traveling in nerves and uses an internal stimulus to reactivate paralyzed muscles that restore movement in individuals partially paralyzed by neurological impairments, such as stroke and multiple sclerosis. Patients with foot drop lose some of the neural connections that allow them to flex hip and knee muscles to swing the leg forward, as well as the ability to control the ankle flexor muscles that lift the foot.

To correct this disrupted circuit, the device amplifies sensory signals in the microvolt range that are generated by skin receptors in the foot and travel along a nerve in the leg, using patented nerve cuff electrodes, also pioneered by Hoffer. The device then detects events, such as the time when the heel contacts the ground, from the sensory input from the foot and it stimulates nerves connected to the paralyzed muscles in order to lift the foot.

While the concept of stimulating nerves in the paralyzed muscle is not new, no other available technology restores movement using internal sensing and stimulation without the need for additional external equipment. "The implanting concept took time to achieve,” Hoffer explains, "even though it was suggested thirty years ago that a fully implanted device would be ideal to assist foot drop.”

The benefits of Hoffer's technological innovations were well worth the wait. In contrast to currently available devices, Hoffer explains that an implanted device requires no external equipment, allowing for greater independence, balance, and comfort that are constantly available, even in unexpected and urgent situations. The lack of external equipment negates the need for shoes and allows for use in the shower. Stimulating paralyzed muscles also rebuilds disused muscles, increasing their size, strength, and resistance to fatigue.

Although not all patients with foot drop would be candidates for a Neurostep implant due to the degree of impairment induced by a stroke or surgical risks related to other medical conditions like diabetes, the device holds potential for restoring movement in a significant number of partially paralyzed patients.

Hoffer's current research aims to improve the implanting procedure through nerve imaging technology and to recharge batteries for implantable devices by harvesting electricity from human motion energy during activities like walking.

Beryl Hatton is completing a Ph.D. in molecular and cellular biology at the University of Washington and Fred Hutchinson Cancer Research Center in Seattle.

Image:

The Neurostep activates paralyzed muscles by amplifying sensory signals generated by skin pressure receptors within the foot when a person is standing or walking. The device uses patented nerve cuff technology also developed by Hoffer to connect the device to two nerves in the leg. One nerve detects signals from the foot while the other activates the muscles that lift the foot. The Neurostep device completes the disrupted circuit to control the walking motion. Image: U.S. Patent application number 20050010265 filed April 2, 2004, published 13 January 2005.