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For lower limb amputees, the loss of sensory information while walking can cause an array of gait deficits and mobility issues, such as shortened stride length, gait asymmetry and slower walking speeds, especially for new amputees who are learning to walk with a prosthesis.

To address these deficits, a team of researchers at the University of California, Los Angeles (UCLA) developed a tactile feedback system to improve the user’s sensory awareness of his or her prosthetic leg. The project originated in 2007 at UCLA’s Center for Advanced Surgical and Intervention Technology (CASIT), and in 2011, Zach McKinney, a graduate student studying biomedical engineering at UCLA, inherited the project.

“My predecessor, Richard Fan, was a PhD student at CASIT before me and did most of the early development, developing the core electronics and software,” McKinney told O&P Business News. “I have taken over the system and made a handful of engineering improvements and continued the line of research.”

 

Zach McKinney

 

UCLA has also partnered with researchers at Naval Medical Center San Diego (NMCSD) to develop and test the device.

 

Tactile feedback system

The system consists of three modules. The first is a sensorized insole worn in the patient’s shoe, which uses pressure sensors to measure the distribution of forces in four locations: the heel, big toe, and left and right sides of the ball of the foot. This information is transmitted wirelessly via Bluetooth to a microcomputer worn around the patient’s waist, where is it immediately processed and translated to the third module, the tactile interface. This module, which is worn as a cuff around the thigh of the patient’s residual limb, contains four arrays of three dime-sized silicone balloon elements, which correspond to the four sensors on the shoe insole.

“They wear a foot switch in their shoe, and the foot switch tells the cuff what is touching the ground,” Marilynn Wyatt, PT, the director of the gait analysis laboratory at NMCSD, said. “At heel strike, they get a sensation on one part of their leg, and at toe strike, they get a sensation on another part of the leg. This device tells their brain which part of the foot has touched the ground.”

At any given time, each of the four balloon arrays will inflate a number of balloons according to the magnitude of force measured by the corresponding foot sensor.

 

“The patient feels pressure on the skin via the inflating balloon elements that are worn against the skin,” McKinney said. “It improves sensory integration between the user and the prosthetic limb, because the tactile stimulation that the patient feels is directly linked to the forces being experienced by their body or the extension of their body, the prosthetic limb.”

Clinical testing

McKinney and his colleagues tested the tactile feedback system on patients with unilateral transtibial amputations receiving rehabilitative care at NMCSD. Gait information was first recorded as the participants walked with their regularly used prosthesis. The participants were then fitted with the tactile feedback system and given an acclimation period to adjust to the device. The researchers then re-recorded gait information as the patients walked at a self-selected speed with the tactile feedback system.

 
 

Full tactile feedback system, worn by a transtibial amputee, improves sensory integration.

Images: McKinney Z.

 

 

Although the study is still ongoing and specific results have not been released, the initial results look promising.

“The data is still preliminary, but we are getting positive feedback on the device,” Wyatt said. “The patients like the feedback [from wearing the device].”

According to McKinney, all of the study participants to date have been healthy, active individuals who are already adept at walking with a prosthesis, so this device might be even more beneficial for a civilian population.

 

“These patients are primarily young and active and have some of the best physical rehabilitation that there is,” McKinney said. “So there is perhaps even more potential for patients who are not as healthy or active or may not necessarily have as a good of a rehab infrastructure around them.”

They are also exploring whether this technology would be beneficial for neuropathic patients.

“The most inclusive way to [describe the target population for this device would be those with] lower limb sensory loss,” McKinney said. “Amputation is obviously the extreme case because they have lost the actual limb, but any sort of neurological sensory loss would apply. So we are branching into another arm of the project where we are trying to explore its value for neuropathy conditions,” McKinney added.

Commercialization

Currently, this device is only intended for use with transtibial prostheses, but McKinney hopes to figure out a way to integrate the device into a transfemoral prosthesis.

 

The sensor module, as worn by an amputee patient, tells the system what is touching the ground.

 

 

“We would have to do it in a way that does not interfere with the function and fit of the socket,” McKinney said. “We would need to make sure that our balloon elements can still be felt and don’t interfere with the patient’s other sensations through the socket interface.”

Eventually, McKinney hopes the tactile feedback device will be available commercially. A medical device company has already shown interest in developing it, but McKinney is unsure of when that will become a reality.

“The device is very much in an investigational stage, and there is a lot of research that remains to be done in terms of proving the value, and we are working in that direction” McKinney said. “But the vision for this technology is to make it a commercially available device that could be used either by therapists in a rehabilitation setting or even by individual users in a home environment.” — by Megan Gilbride

Disclosure: The researchers have no relevant financial disclosures.

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