Can Tibion’s Bionic Leg Rewire Stroke Victims’ Brains?

The conventional wisdom about stroke victims is that after about 12 months of rehabilitation aimed at restoring motor control, recovery levels off. Patients never regain more movement, never get beyond whatever plateau they’ve reached by that time.

But there’s a company in Sunnyvale, CA, that may be proving otherwise. Tibion makes a robotic, battery-powered exoskeleton—in effect, a wearable bionic leg—that’s helping stroke victims make significant gains long after other therapies have stopped working.

The Tibion leg isn’t something stroke patients wear continuously. It’s meant as a new tool for physical therapy clinics, where patients with one-sided weakness, or hemiparesis, wear the device for 15 minutes at a time, three times a week. Only a few hundred patients have used it so far, but after just 12 sessions with the device, most patients studied have gained significant walking speed. One patient improved from 0.6 meters per second to 0.8, another from 0.8 to 1.0. (A normal walking speed is about 1.2 meters per second). Most importantly, these gains held—and, indeed, seemed to unleash further recovery. Six months after his sessions with the Tibion leg, the patient who had reached 0.8 meters per second had accelerated to 0.95 meters per second, according to Charles Remsberg, a veteran of the medical-device industry who joined Tibion as CEO in 2009.

It took some ingenious engineering simply to make the Tibion leg powerful enough to lift someone out of a chair, while still being compact enough to wear. But the company thinks that a different feature is what makes the device so effective at spurring motor recovery: sensors that allow the device to respond to patients’ intentions.

The Tibion robotic exoskeletonStrokes damage the neural pathways in the brain responsible for executing motor movements—meaning that “All the thinking in the world that ‘I am going to use my leg’ will not allow an affected leg to support you in standing,” as Remsberg puts it. But a pressure sensor placed inside a patient’s shoe and attached to the Tibion leg’s electronics can detect even a slight shift in weight—the first stage in standing up from a sitting position or taking a step. Such a shift triggers the robotic leg to extend, raising a patient up or swinging their leg forward. And this movement provides proprioceptive feedback that, over time, helps patients’ brains rewire themselves, so that they are eventually able to carry out the motion on their own.

At least, that’s the theory. “I can’t tell you for a fact, but the hypothesis is that we are amplifying residual intention,” says Remsberg. “This allows for an intensive level of training, which appears to capitalize on neuroplasticity, the ability of the brain to rewire around regions destroyed by stroke.” (Remsberg expands on this idea in the video on page 3.)

If larger studies prove that the device is as effective as the early results seem to suggest, Tibion exoskeletons could become standard equipment at the 15,000 skilled nursing facilities and 2,000 rehabilitation hospitals in the United States. And that could be big business for Tibion, which raised Series A funding from Oakland, CA-based Claremont Creek Ventures in 2006, as well as a $3 million “Series A extension” this May. (Remsberg himself contributed to the May round, and is the startup’s third largest shareholder.) The list price of a Tibion leg is $40,000, but the company rents them out for $700 to $1,000 per month, depending on … Next Page »

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Wade Roush is a contributing editor at Xconomy. Follow @wroush

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